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Publication of this paper has been assisted by a grant from the Victoria University of Wellington Publications Fund. Material described here was in part assembled with the aid of a grant, enabling travel to Australia, from the Victoria University of Wellington.
Of twelve leptocephali from the New Caledonia area, myotome counts, etc., firmly identify two as Anguilla megastoma, three as A. australis, one as A. obscura, but six, recognisable as long-finned larvae and associated with A. marmorata and A. reinhardti cannot be assigned definitely to either of these species. Two glass-eels from near Sydney are referred to A. australis ?australis on geographic grounds. Including the four Dana leptocephali of
In the course of a study of New Zealand eels, a small collection of eel larvae, about 20 specimens in number, was assembled from various sources in this country. During the early stages of identification and description of these specimens several large collections of leptocephali were made available to the author for study purposes from institutions outside New Zealand—namely, (a) the Centre d'Océanographie de l'Institut Française d'Océanie, Nouméa, New Caledonia, (b) the C.S.I.R.O. Division of Fisheries and Oceanography, Cronulla, New South Wales, (c) the Australian Museum, Sydney, and (d) the Western Australian Museum, Perth. At the time of writing the total number of leptocephali assembled by the author is about 1100 specimens. The present paper, however, deals with only a small fraction of this number, some 14 specimens, belonging to the genus Anguilla Shaw and referable to four or five of the six known Australasian species. This group of larvae was chosen for study before others because Anguilla, more than any other genus of eels, is the most completely known. Eel larvae are often difficult to identify, mainly due to insufficient knowledge of the adults. The species of Anguilla, however, have been so well described (Ege, Dana collection (1500 specimens) serves as a most valuable reference in this present work.
The author would here like to express his warmest thanks to the authorities of the above institutions who kindly placed their collections on loan; to Mr M. Legand (I.F.O., Nouméa), Mr I. S. R. Munro (Div. Fish. Oceanogr., Cronulla), Mr G. P. Whitley (Australian Museum, Sydney) and Dr R. W. George (Western Australian Museum, Perth) without whose individual interest this study would not have been possible; finally, Prof. L. R. Richardson, of the Department of Zoology, Victoria University of Wellington, for his welcome criticisms.
The present collections from the Australian region include about 550 leptocephali, but only one of these leptocephali is referable to the genus Anguilla; two others are glass-eels or virtually unpigmented elvers. These three specimens were collected on the east coast of Australia. Eleven other Anguilla leptocephali were taken in the New Caledonia-Solomons-New Hebrides area as part of a collection of about 550 specimens.
Where possible, preserved leptocephali were transferred to and held in a mixture to the formula given in Lea (
Specimens were examined under a low-power binocular microscope with both transmitted and reflected light, the latter being particularly useful in observing teeth and in counting myomeres. Drawings were made with the aid of a camera lucida. Some specimens were stained in acetic acid-alum-carmine and cleared in glycerine for examination of structures in the alimentary, renal and vascular systems.
Total lengths were measured to the nearest 0.1mm by placing the specimen on a piece of white, waxed card and using pins to indicate the extremities; total length was measured from the tip of the upper jaw to the tip of the caudal fin. Contraction in length on preservation has been observed in Anguilla leptocephali by Jespersen (1 + h2 + h3 etc., where h1 is the upper. Teeth are counted on the left side in both upper and lower jaws in the manner of Jespersen (Anguilla but occurs very similarly throughout the larvae of many different eels.
Identification of leptocephali to the species level is often a difficult task. The relatively few characters which are associated with a certain form of leptocephalus—e.g., disposition of melanophores and vertical intestinal blood-vessels, dentition, shape of caudal fin, always fail to survive the metamorphosis from the larva to the juvenile eel. In only a few species have a series of transitional stages been collected and the complete metamorphosis worked out. Transitional forms are in many cases active, bottom-dwelling and more easily escape trawls than do the leptocephali.
Fortunately, however, there is one major, accessible character which continues on from the larva, through the metamorphosis, to the juvenile and the adult. This is the number of myomeres (actually postcranial segments). Other characters such as fin-rays and branchiostegal rays also appear unchanged in number
In counting segments the first full segment is taken as the most anterior myomere extending at least to the level of the notochord and the last taken as that indicated by the last spinal ganglion. Spinal ganglia are indeed often easier to count than the myomeres. In eels the number of vertebrae is usually one less than the number of myomeres in the larvae, and this has been taken into account when referring the leptocephali to their adult species. Preanal myomeres are counted to a vertical through the vent; usually the vertical falls on the middle of a myomere at the lateral midline, and in these cases this myomere is included in the preanal number. All segments posterior to this are regarded as postanal. The distance between the dorsal and anal origins, or a–d, is expressed as the number of segments counted between the verticals through these origins.
In all leptocephali the viscera are supplied by a number of median blood-vessels from the aorta; these are referred to in this study as the "vertical blood-vessels". The positions of these vessels—there may be few to many—provide a valuable specific character. Usually the first vessel (to the anterior margin of the liver) and the last (to the posterior margin of the opisthonephros) are the most conspicuous and more readily observed. The position of each vessel is indicated by the myomere level at which it lies—e.g., 17, 25, 41, being the junction of the vessel with the aorta. In the case where a vessel is situated level with a myoseptum the level is indicated by the two nearest myomeres—e.g., 41–42.
Opinion 44 (Leptocephalus Gronovius, L. morrisii was indeed a young conger. This action was reversed by Opinion 93 (Conger Cuvier, Conger Oken, Leptocephalus reserved for the larval form. While a number of attempts have been made to group larval eels into various genera and subgenera, the present author follows the simple course of referring all species to the genus Leptocephalus. In naming leptocephali it has often been the practice to use the clumsy genitive form for leptocephali whose adults are known—e.g., Leptocephalus Anguillae marmoratae. The author proposes to follow Bruun (Leptocephalus Anguilla marmorata or more simply L. Anguilla marmorata.
The genus Anguilla Shaw, the sole representative of the Family Anguillidae, has become, with the exhaustive researches of Danish scientists, the most intimately-known genus of eels. The two Atlantic species A. anguilla (L.) and A. rostrata (Le Sueur) were studied thoroughly by Johannes Schmidt over a long period of years, initiating a great deal of further work. His collections formed the basis of a definitive study of the systematics of the genus by Ege (
Ege (Anguilla species present in the Southwest Pacific. Four of these are long-finned species—that is, with the origin of the dorsal fin conspicuously in advance of the level of the anal origin. These
A. megastoma Kaup with an average of 112 vertebrae and known from the Solomons to Pitcairn; A. marmorata Quoy & Gaimard with about 106 vertebrae and distributed widely throughout the Indo-Pacific from Africa to the Marquesas but not reaching south of New Caledonia or New Guinea in the Southwest Pacific; A. reinhardti Stcindachner with about 108 vertebrae, confined to New Caledonia and eastern Australia from Cape York to Victoria; and A. dieffenbachi Gray with about 113 vertebrae, restricted to New Zealand. The remaining two species are short-finned eels with the dorsal origin only a little in advance of the level of the anal origin. These are: A. australis Richardson with about 112 vertebrae and present in Fiji, New Caledonia, Southeast Australia and possibly Tahiti; and A. obscura Günther with about 104 vertebrae, occurring from Tahiti through Fiji, New Caledonia, North Queensland and New Guinea.
Despite this widespread occurrence of so many species of Anguilla in the South Pacific only four anguillid leptocephali have ever been recorded from this area; these were from the Dana collection (see Jespersen, Anguilla larvae were taken by the Dana in the whole of the Indo-Pacific. The South Pacific area was widely explored by this vessel during the months of Anguilla larvae in this area may have been due to the time of year when the trawling took place. The larvae described here, 12 in number, therefore make a significant addition to knowledge of the South Pacific species of Anguilla. These larvae were collected in similar depths to those of the Dana larvae and in various months of the year, so that Jespersen's assumption is not supported by the present collection.
Material Examined. Two specimens, 23.7mm and 26.4mm total lengths; Institut Français d'Océanie Station 56–4–3; 12° 55′ S., 170° 04′ E.;
Description. Measurements in mm: total length 26.4 (23.7), head 2.7 (2.7), snout 0.9 (0.9), eye 0.5 (0.6), upper jaw 1.0 (1.0), postorbital 1.3 (1.2), pectoral 0.9 (0.8), preanal 18.8 (17.4), predorsal 16.8 (16.2), depth just before eye 1.2 (1.0), depth at pectoral origin 2.2 (3.1), depth at midpoint between pectoral and vent 4.6 (4.2), depth at anal origin 4.4 (3.2). Branchiostegal and pectoral rays not obvious, dorsal and anal elements visible only near tip of caudal region, caudal rays 2 + 2 + 2 + 2 + 1. Teeth . Myomeres 72 + 39 = 111 (114). a–d = 7 (7). 1st vertical blood-vessel at 17th myomere, 2nd at 42nd and 3rd at 48th. Anterior margin of gall-bladder at level of 29th myomere.
Body elongate but not excessively so, much compressed, not very deep and tapering a little more gradually in front of midpoint of body. Head short, about one-ninth of total length, its lower profile indented at the throat to make the head region clearly differentiated from the trunk; snout short, equal to one-third of head length, acutely pointed with its dorsal profile conspicuously concave and anterior and posterior nares almost separated; eye moderate, oval, with its greatest diameter vertical and a little less than length of snout; gape oblique, extending to level of anterior margin of eye; teeth relatively large, very acute, eight in the upper jaw, projecting outside the six of the lower jaw and distributed as follows: a large, forwardly-projecting grasping tooth is preceded by a tiny, needle-like tooth placed almost on the dorsal surface of the snout and is followed by three large teeth which become progressively smaller; this series is followed by three noticeably smaller teeth, the most posterior of which is placed almost directly under the anterior rim of the orbit; the teeth of the lower jaw are similar in
Colour in preservative translucent, with black pigment confined to the chorioid of the eye.
Remarks. The two specimens described here belong unquestionably to the genus Anguilla. They agree very well with Group I (Anguillidae) of Ancona (Anguilla larvae, 111 and 114, suggesting that they are the young of either A. dieffenbachi (109–116 vertebrae) or A. megastoma (108–116 vertebrae). They were both collected at the same station, north-east of the New Hebrides, which is well outside the known distribution of A. dieffenbachi (a species restricted to New Zealand). Although the position of capture does not entirely rule out the possibility that they are the young of the latter species, since its breeding area is possibly as far north as New Caledonia, I am satisfied mainly for geographical reasons that the two larvae are the young of the other long-finned species with a high number of vertebrae—i.e., A. megastoma.
The two specimens of A. megastoma described above are evidently about half-grown, possessing only a few teeth (8–9) compared with the average full complement of about 18–20 in Anguilla larvae about to undergo metamorphosis. In both specimens the olfactory organ is not well developed, but in the larger the anterior and posterior nares are near to separation; the vertebral column is well chondrified; the vent is not greatly posterior; the heart is well developed, and the cranium well ossified.
Material Examined. One specimen, 27.3mm total length; IFO St. Ep 27b(l) ; 17° 13′ S., 162° 30′ E.;
Description. Measurements in mm: total length 39.2 (27.3–43.6), head 3.8 (3.1–4.0), snout 1.2 (1.1–1.7), eye 0.8 (0.9–1.0), upper jaw 1.9 (1.4–2.1), postorbital 1.9 (1.3–2.0), pectoral 0.9 (0.6–1.2), preanal 30.9 (21.3–33.6), predorsal 25.8 (19.6–31.1), depth just before eye 1.7 (1.5–2.1), depth at pectoral origin 3.4 (2.4–4.0), depth at midpoint between pectoral and vent 8.6 (5.0–8.8),
Body elongate, but not excessively so, much compressed but relatively deep, its maximum depth contained a little more than four times in the total length, tapering equally in front of and behind midpoint of body. Head short, about one-tenth of total length, indented at the throat, pointed, with the dorsal profile slightly convex; anterior and posterior nostrils clearly separated; eye contained one and a-half times in snout, oval, with the greatest diameter vertical; cleft of mouth oblique, extending to level of middle of pupil; teeth conspicuous, very acute, 18 in upper jaw projecting outside those of lower jaw, distributed as follows: first tooth minute, needle-like, directed immediately forwards and placed on the anterodorsal surface of the snout above the second tooth, which is a much larger anteriorly-directed grasping tooth; these two are followed by a second series of large, needle-like fangs and a third of much smaller teeth to a point below the middle of the pupil; the teeth of the lower jaw are similar in grouping and size to those of the upper jaw. Branchiostegal rays not obvious. Pectoral fin large, about equal to vertical diameter of eye, rounded, base of fin fleshy but with the rays not obvious. Dorsal fin low with the rays well developed only in the larger specimens but the radials always countable. Anal fin a little higher than the dorsal. Caudal fin in the larger specimens well marked off from the dorsal and anal fins and with well developed hypurals and fin-rays.
Colour in preservative translucent with pigment restricted to the chorioid of the eye.
Remarks. These six specimens are long-finned larvae, having 8–9 myomeres between the origins of the dorsal and anal fins compared with about 5 in short-finned species. They have 106–110 myomeres. These two characters, taken together with the location of capture of the six larvae, restrict the identification to either A. reinhardti or A. marmorata. However, it is difficult to refer these larvae further to either one or other of these two species or both since the definitive adult characters are relatively insignificant and are not exhibited in the larvae. There is evidence, nevertheless, to show that these larvae represent two species. I have examined a large number of leptocephali of the Genus Gnathophis (Congridae) including a wide range of sizes for two species. In this case, the segmental level of the gall-bladder is the same in both species and does not change with growth. In the present six specimens, the two smallest larvae (27.3mm and 27.6mm) have the gall-bladder at the level of the 31st myomere, but in the other four specimens the gall-bladder is level with myomeres 24 and 25. From this I consider that there are two species in this particular group of six larvae. The two smallest larvae with a more posterior gall-bladder were collected in the northerly region of the area known for the adult A. reinhardti. The four larger were taken in the southern part of the known distribution of A. marmorata. Since the areas occupied by the adults overlap only in New Caledonia, and since two larval species are indicated, further work may confirm my proposed identifications.
Material Examined. One specimen, 24.6mm total length; IFO St. 56–4–2; 14° 37′ S., 170° 03′ E.;
Description. Measurements in mm: total length 47.6 (24.6), head 4.3 (2.8), snout 1.0 (1.2), eye 0.7 (0.6), upper jaw 1.6 (1.2), postorbital 2.4 (1.2), pectoral 1.1 (0.5), preanal 29.6 (19.2), predorsal 27.0 (18.2), depth just before eye 1.8 (1.2), depth at pectoral origin 3.4 (2.0), depth at midpoint between pectoral and vent 8.5 (4.2), depth at anal origin 9.4 (4.1). Branchiostegal rays 12 (−), pectoral rays 17 (−), dorsal rays before level of vent 26 (−), total rays 194 (−), 1st dorsal ray at level of myomere 58; anal rays 187 (−), caudal rays 2 + 2 + 2 + 2. Teeth none and . Myomeres 62 + 54 = 116 (112). a–d = 3 (2). Vertical blood-vessels at myomeres 17, 41, 48 (17, ? 48). Anterior margin of gall-bladder at myomere 27 in one specimen, obscured in the larger specimen.
Body not excessively elongate, much compressed except along the head but relatively deep with the maximum depth contained about five times in total length; tapering about equally in front of and behind the midpoint of the body. Head short, about one-tenth of total, slightly indented at the throat: snout about one-fourth of head, rounded, with a slightly convex dorsal profile and both nostrils well separated; eye contained 1.3 times in snout, oval, with the greatest diameter vertical; cleft of mouth oblique, extending to level of middle of pupil; teeth absent in the larger specimen, but eight small cavities remain in the lower jaw. Branchiostegal rays well developed and curving across the space in front of pectoral. Pectoral fin just less than snout and eye combined, rounded, base of fin fleshy. Dorsal fin low, with the radials visible throughout as well as most of the rays. Anal fin conspicuously higher than the dorsal. Caudal fin not greatly differentiated from the dorsal and anal.
Colour translucent with pigment restricted to the chorioid of the eye.
Remarks. These two leptocephali are short-finned, having the difference between the dorsal and anal origins equal to three myomeres. The two species of short-finned eels present in the south-west Pacific are A. australis with 108–116 vertebrae and A. obscura with 101–107 vertebrae. The two larvae have 112 and 116 myomeres and are therefore referred to A. australis. Two subspecies of A. australis have been recognised: A. australis australis Richardson in New South Wales, Victoria, Tasmania and Lord Howe Island and A. australis schmidti Phillipps from New Zealand and outlying islands, Norfolk Island, New Caledonia, Fiji, and possibly Tahiti. The larger specimen of these two larvae, almost at metamorphosis, was taken very close to New Caledonia and is probably A. australis schmidti. The smaller specimen was taken far from the area known for the adult of the Australian subspecies and is also tentatively referred to A. australis schmidti.
Material Examined. One specimen, 75.7mm total length; Aust. Mus. regd. no. IA.2363; McCulloch Reef, Great Barrier Reef, Queensland, between 17° S. and 19° S.; transitional larva.
Description. Measurements in mm: standard length 74.9, head 5.8, snout 1.0, eye 1.1, interorbital 1.0, upper jaw 2.3, postorbital 4.0, pectoral 1.3, preanal 41.8, predorsal 40.3, depth just before eye 2.0, depth at pectoral origin 3.2, depth at anal origin 5.2. Myomeres 52 + 60 = 112. a–d = 1.
Body moderately elongate, compressed, tapering appreciably only at head and along posterior half of caudal region. Head short, about one-thirteenth of total length, not greatly differentiated from trunk; snout acute, one-sixth of head, projecting in front of lower jaw and turned noticeably downwards; nostrils well separated with the anterior one almost at tip of snout, the other just in advance of eye; eye round, about equal to length of snout; gape considerably oblique, extending to a point just in advance of pupil. Teeth difficult to distinguish. Pectoral a little longer than snout; dorsal low, originating only slightly in advance of level of vent; anal also low; caudal fin distinct from tips of dorsal and anal. Colour creamy brown with black pigment restricted to the chorioid of the eye.
Remarks. This specimen is a late leptocephalus which has taken on the elongate form of the elver. It has not yet become rounded in cross-section but is losing its transparency. The preanal myomeres number 52, compared with 39 in the elver. With a total of 112 myomeres and a short dorsal fin there is little doubt that the specimen belongs to A. australis and, considering its point of capture close in to the Queensland coast, to the Australian subspecies, A. australis australis. The specimen is not in the best condition and shows no distinctions from the larvae assigned to A. australis schmidti enabling certainty of subspecific identification.
Material Examined. Two specimens, 52.5mm and 57.9mm total lengths, Aust. Mus. regd. no. IB.5289; rock-pool, Forty Baskets Beach, Sydney;
Description. Measurements in mm: total length 57.9 (52.5), head 6.0 (6.0), snout 1.4 (1.1), eye 0.6 (0.7), interorbital 0.3 (0.3), upper jaw 1.4 (1.7), postorbital 4.3 (4.1), pectoral 1.1 (1.2), preanal 20.0 (−), predorsal 19.8 (−), depth just before eye 1.0 (0.8), depth at pectoral origin 1.8 (1.8), depth at midpoint between pectoral and vent 1.5 (1.5), depth at anal origin 1.4 (1.7). Branchiostegal rays 12 (12), pectoral rays 19 (18), dorsal rays before level of vent 9 (8), total rays ca. 193 (211), anal rays ca. 186 (203), caudal rays 2 + 2 + 2 + 2 (2 + 2 + 3 + 2). Teeth . Myomeres 39 + 74 = 113 (110). a–d = 2 (2).
Body greatly elongate, cylindrical, compressed only near tip of caudal region, tapering only at snout and at tip of caudal. Head long, about one-tenth of total length, slightly swollen in front of pectoral but otherwise little differentiated from trunk; snout rounded, less than one-quarter of head length with anterior nostril far forward on tip of snout, posterior nostril a little in advance of eye; eye less than twice in snout or about seven times in postorbital, circular; gape oblique, extending to just behind forward margin of eye, lower jaw projecting for a distance equal to length of pupil. Teeth bluntly conical, short, sparse, uniserial, unlike those of the leptocephali; distributed as follows: on the maxilla five small teeth are followed by two larger ones posteriorly, while on the dentary there are ten small teeth anteriorly and two larger ones posteriorly. Pectoral fin about equal to snout, oval. Dorsal fin low, originating only a short distance in advance of the anal; anal fin also low, caudal fin well differentiated from the tips of the dorsal and anal fins.
Colour in preservative restricted to a few large melanophores on the lateral surface of the head, a continuous series of deeply-placed, expanded melanophores on the spinal cord beginning at the level of the pectoral fin through to the tip of the caudal region, a scattering of pigment laterally on the tip of the caudal region and on the caudal fin as well as a pigmented chorioid.
Remarks. The specimens described here are transitional elvers between Stage V and Stage VI of Strubberg (A. australis. They were collected at Sydney, New South Wales, and therefore fall well within the geographical range known for the Australian subspecies, A. australis australis.
Material Examined. One specimen, 49.6mm total length; IFO St. G 16; 16° 52′ S., 166° 26′ E;
Description. Measurements in mm: head 4.0, snout 1.1, eye 0.9, upper jaw 1.8, postorbital 2.4, pectoral 1.0, preanal 36.1, predorsal 33.3, depth just before eye 1.4, depth at pectoral origin 3.0, depth at midpoint between pectoral and vent 8.8, depth at anal origin 7.6. Branchiostegal rays 8; pectoral rays not obvious; dorsal rays before level of vent 59, total rays 216, 1st dorsal ray at myomere 63; anal rays 204; caudal rays 2 + 2 + 2 + 2. Teeth . Myomeres 70 + 33 = 103. a–d = 5. Vertical blood-vessels at 17, 37, 43.
Body moderately elongate, much compressed, deep, with the greatest depth contained five times in total length. Head short, about one-eleventh of total length, rather depressed so that it is well differentiated from trunk; snout short, about one-fourth of head length, its dorsal profile convex; anterior and posterior nostrils well separated; eye about equal to length of snout, oval; cleft of mouth oblique, extending almost to level of posterior margin of eye; teeth conspicuous, very acute, 18 in upper jaw projecting outside those of lower jaw which number about 13, distributed as follows: first tooth of upper jaw small, needle-like, directed anteriorly and placed immediately above the second, much larger, anteriorly-directed grasping tooth; these two are followed by a series of four large teeth and a final series of 12 noticeably smaller teeth; lower teeth similar to those of upper jaw with the absence of the needle-like anterior tooth. Branchiostegal rays delicate and curving up around the operculum. Pectoral fin about 1.5 times diameter of eye, rounded, fleshy. Median fins well developed with fin rays and radials clearly visible.
Colour in preservative translucent with black pigment restricted to the chorioid of the eye.
Remarks. The specimen belongs to a short-finned species, having five myomeres between the levels of the dorsal and anal origins. The myomeres number 103, and this character fully identifies the specimen with A. obscura which has 101–107 vertebrae. The specimen is well advanced in development having very nearly a full complement of teeth, well developed fin-rays, etc., and the vent placed half way between the midpoint of the body and the tip of the caudal region.
The twelve leptccephali dealt with above plus the four specimens from the Dana collection giving a total of 16 known specimens of anguillid larvae from the Southwest Pacific contrasts strongly with the richness of collections of this family in other ocean areas. This is the more interesting because the area contains six known species, all of which are common in the freshwaters of the area. There is no uncertainty in sorting these few larvae into long-finned and short-finned categories. Within these groups, four larvae can be identified as the short-finned A. obscura (one specimen) and A, australis (three specimens) since the number
A. australis.
Of the eight long-finned larvae two are here identified with A. megastoma, since these two specimens were taken much further to the north of the observed geographic range of A. dieffenbachi with which the larvae of A. megastoma could be confused. The six remaining specimens belong either to A. marmorata or A. reinhardti although certain differences in morphology and geographical reasons suggest that four of these are A. marmorata and two A. reinhardti.
Although there are no very early larvae in this collection, the smallest being 23.7mm (A. megastoma, it may be significant in determining the location of the breeding areas of the various species that all the smaller larvae were collected to the east of the larger larvae (with the exception of the Dana specimen of A. obscura, 43mm). Taking into consideration the general east-west trend of the prevailing current system in this area it seems likely that the breeding area for these species is well to the east of New Caledonia—that is, between Fiji and Tahiti.
All of these Anguilla larvae were collected in depths of about 100m-200m where the temperature is at least 20°C. and the salinity is about 35.5%o. Conditions such as these are known to occur in the breeding areas of the Atlantic species of Anguilla.
In 11 early elvers of A. australis australis from the New South Wales region Ege (A. australis schmidti from New Caledonia reach an average maximum of about 50mm, while those of this species from New Zealand reach a much greater average length, about 61mm. As Ege (Anguilla in the Pacific. A. japonica Temminck & Schlegel from Japan has elvers which reach about 57mm (Ege, A. dieffenbachi from New Zealand reach about 64mm-70mm. It is possible that the temperate elvers are more distant from the breeding grounds of the adults than are their tropical counterparts, and this may account for their larger average size.
This key has been prepared from the 16 known Anguilla larvae from this area; the number of myomeres in each species (one more than the number of vertebrae) has been taken from the observed range of variation in the vertebral count of the adult. The key is simple to use. Where there is agreement at one number, proceed to the consecutive number; where there is no agreement, proceed to the alternative indicated in parentheses.
Publication of this paper has been assisted by a grant from the Victoria University of Wellington Publications Fund. Material described here was in part assembled with the aid of a grant, enabling travel to Australia, from the Victoria University of Wellington.
Gnathophis habenatus habenatus (Richardson, Gnathophis h. longicaudatus (Ramsay & Ogilby, G. heterognathus and G. nystromi and the Californian G. catalinensis in a short preanal region, less than 40% of total length. Both subspecies have 120–129 vertebrae, scroll-like anterior nostrils and an inconspicuous, triangular premaxillary-ethmoid patch of teeth, distinct from G. incognitus n. sp., the adult as yet known only from New Zealand waters, which has 139–147 vertebrae, anterior nostril with a simple, free flap, externally obvious premaxillary-ethmoid patch of teeth, minute, scattered epidermal papillae and preanal region usually less than 40% of total length.
Size-range of leptocephali indicate spawning off New South Wales and Western Australia, metamorphosis at about 80mm and characteristically a posterior vent, somatic pigment as a ventral, regular series at the level of the simple intestine, small pigment crescent below iris and in the largest larvae, a pigment spot at the base of most anal rays.
Among the fishes collected by the vessels H.M.S. Erebus and H.M.S. Terror while they were in New Zealand waters during the years Congrus habenatus. The type specimen was taken in "Cook's Strait", but no more precise locality was given. Since the time of Richardson's account the "little conger" or "silver conger", as the species has come to be known by fishermen and others, has occasionally appeared in seine nets, trawls and fish stomachs from other parts of the New Zealand coast as well as from the Cook Strait area. The silver conger is also well-known in southeast Australia. Such an eel cannot easily be confused with other eels of these regions in view of its remarkably bright silver colouration over the anterior part of the body and particularly the iris making this a most attractive and easily-remembered fish.
Although Richardson's Congrus habenatus is thus well-recognised from Australasian coastal waters there has always been considerable systematic confusion, involving some nine generic names, in the correct name of this animal and related species elsewhere. This paper finally resolves this confusion; but further, early in the examination of numerous specimens of the silver conger from the New Zealand region, it was found that a second, unrecognised species was also present in the area and this is described and figured here.
In the preparation of this paper I have been able to examine 33 juveniles and adults of the two species, most of which were taken in seine nets in Wellington
Proportional measurements were made to the nearest 0.1mm with accurate calipers in the manner I have already described (Castle,
I am greatly indebted to the following institutions and persons who have helped in many ways in the preparation of this account. Firstly, to those institutions which have so generously allowed me to examine leptocephali or adults in their collections (a) the C.S.I.R.O. Division of Fisheries and Oceanography, Cronulla, New South Wales, (b) the Centre d'Océanographie de l'Institut Français d'Océanie, Nouméa, New Caledonia, (c) the Australian Museum, Sydney, (d) the Western Australian Museum, Perth, (e) the Dominion Museum, Canterbury Museum and Otago Museum, New Zealand; secondly, to Mr R. H. Kanazawa, Division of Fishes, U.S. National Museum, Washington, for valuable comments on the distinctions of various genera of eels and for literature; Dr J. C. Yaldwyn, Australian Museum, for examining the type of Congromuraena longicauda; finally, to Prof. L. R. Richardson, Department of Zoology, for his valuable criticisms.
Günther's Catalogue of the Fishes of the British Museum (Congrus habenatus a species which had been described as Myrophis heterognathos by Bleeker (Gnathophis on Bleeker's species, clearly distinguishing Gnathophis from Myrophis Lütken, Myrophis indeed does not have the prong-like bones in the upper lip. Bleeker (Myrophis (although Schultz et al. (Uroconger Kaup, Myrophis heterognathos as a synonym of Uroconger lepturus (Richardson, Myrophis heterognathos with Asano's description of Uroconger lepturus shows conclusively that the Nagasaki specimen cannot be a Uroconger.
In his useful and detailed account of the Japanese congrid eels Asano recognises on morphological grounds two divisions of the Congridae (a) the Anagostem,
Anago, Ariosoma, Alloconger, Chiloconger and Thyreoconger (which is a synonym of Ariosoma; see Rosenblatt, Conger-stem, including the other congrid genera examined, which all have the supraoccipital bone except Congriscus. Reference may be made to Asano's account for the numerous other characters which serve to distinguish the genera of the two groups. Bleeker's illustration of Myrophis heterognathos shows an eel with the dorsal fin originating over the middle of the pectoral, a character possessed only by Congriscus megastomus, Conger cinereus, Rhynchocymba nystromi, R. xenica and Congrina retrotincta of the Japanese eels; the tail is relatively short, referring it to Congriscus, Conger or Rhynchocymba; the vomerine teeth are molariform and in several rows, while the maxillary teeth are conical, both characters which are indicative of all genera except Uroconger and Congrina; the prong-like preorbital bones are directed forwards and outwards. Uroconger has a dorsal origin over the branchial aperture, a very long tail and preorbital prongs which are directed backwards and outwards; Congriscus and Conger have no preorbital prongs. Myrophis heterognathos can therefore be referred only to Rhynchocymba under Asano's system and clearly not to Uroconger. Since Myrophis heterognathos is the type of Kaup's genus Gnathophis then Rhynchocymba (Jordan & Hubbs,
Returning to Günther's suggestion that Gnathophis heterognathus is very closely similar to the Australasian silver conger, an examination of various osteological characters of the two shows them to be congeneric. The silver conger is immediately referable to Asano's Conger-stem in having a supraoccipital present, a reduced ethmoid process, four suborbital bones and lateral line ossicles of the Conger type. Further, there are three prong-like bony projections into the upper lip from the ventral aspect of the preorbital bone and the upturned labial flange of the upper lip is present but reduced. By Asano's account these characters restrict Richardson's Congrus habenatus to "Rhynchocymba "—i.e., Gnathophis. Phillipps (Gnathophis habenata but Gnathophis is masculine gender and the specific name therefore becomes G. habenatus (Richardson, Gnathophis Is G. heterognathus (Bleeker, G. habenatus as I had already noted in error (
Wade (Gnathophis from the coast of California and thus the distribution of the genus is further extended from the Japanese and New Zealand regions, but the range is probably not confined to the Pacific. It is my opinion that Muraena mystax Delaroche, in lit. variously Congermuraena, Bathycongrus, etc.) is also a Gnathophis but lacking specimens I am unable to confirm this. Lozano Rey (Gnathophis. Further, the larvae of Delaroche's species, as described and figured by Lea (Gnathophis habenatus as described later in this account. They have the vent placed relatively far back (in fully developed larvae), there is a crescentic patch of black pigment below the posteroventral corner of the iris, there is a series of regularly-spaced pigment spots at the level of the intestine along the ventral body-wall and a series of spots on the bases of most anal rays. Although it would be unwise at this stage of knowledge to speculate too much on the relationships of adult eels as shown by
"Muraena" mystax is a species of Gnathophis.
Gnathophis habenatus has been known under a variety of generic names, the first of which is Congermuraena Kaup, Congermuraena (or Congromuraena as emended by Günther, Congrus habenatus but in doing so referred two other species, Muraena balearica Delaroche, Muraena mystax Delaroche, Congermuraena habenata (copied from Richardson) in comparison with only brief mention of the other two species and Bleeker later selected Muraena balearica as the genotype. However, Swainson (Ariosoma from a species well-known from Sicilian shores which was "richly coloured with silver reflections, very different from the lurid hues of the true eels". As Ogilby (Muraena balearica when he established Ariosoma. It is unlikely that he had Muraena mystax in mind since this species has only a silver iris compared with the broad silver colouration in Ariosoma balearica (Lozano Rey, Ariosoma was probably meant to distinguish this genus from Muraena which has conspicuously tubular posterior nostrils.
As Griffin (Muraena balearica as the genotype of Congermuraena makes the latter a synonym of Ariosoma. Griffin recognised the generic distinction of Richardson's Congrus habenatus from Ariosoma balearica and that the former was apparently left without a valid generic name. He therefore proposed Poutawa for this species and thus Poutawa is a synonym of Gnathophis.
Six species are here referred to the genus Gnathophis Kaup, of which two have been each further subdivided into two subspecies. Three of these species are known from the shallow waters of Japan and China: the type species G. heterognathus (Bleeker, G. nystromi (Jordan & Snyder, G. xenicus (Matsubara & Ochiai, G. heterognathus and these are as follows (in per cent total length) : head 17.0, snout 4.3, eye 2.9, cleft of mouth 5.3, pectoral 4.7, predorsal 20.7, preanal 37.3. Jordan & Snyder (G. nystromi: head 16.1, snout 4.6, eye 3.1, cleft of mouth 5.3, pectoral 5.3, predorsal ca. 18.5, preanal 37.5. The number of vertebrae in the latter species is 114–132 (Matsubara & Ochiai, G. heterognathus. Nevertheless, considering the relative abundance of G. nystromi in Japanese waters and that G. heterognathus is still only known from the one specimen, the very close similarity of the two species in proportional measurements indicates that G. nystromi is very probably a synonym of
G. heterognathus. A complete re-examination of Bleeker's type is necessary to confirm or refute this suggestion.
G. nystromi has been divided into two subspecies, G. nystromi nystromi (Jordan & Snyder, G. nystromi ginanago (Asano, G. xenicus, which Matsubara & Ochiai (G. nystromi is distinguished from G. heterognathus-G. nystromi in having a shorter head and a much greater number of vertebrae, 152–154.
One other species has been described from the North Pacific; this is G. catalinensis (Wade, G. catalinensis has the many features characteristic of gnathophid eels, but Wade's illustrations (pl. 26, figs. 1–3, p. 209) show a simple tubular anterior nostril, an inconsistent feature which should be checked in view of the close similarity of this species in other characters to Japanese species. Wade gives the following proportions for the type of G. catalinensis: head 16.8, snout 4.6, eye 3.2, cleft of mouth 5.3, pectoral 6.0, predorsal ca. 18.0, preanal 37.0, vertebrae 132. Wade distinguishes his species from G. nystromi in having "a longer, more pointed vomerine band of teeth, smaller mouth, shorter eye, less projecting snout and a more anteriorly inserted dorsal" but these figures, compared with those given from Jordan & Snyder's account of G. nystromi do not support the distinction. In addition, the vomerine band of teeth in G. nystromi is subject to such variation (Matsubara & Ochiai, G. catalinensis. The relationships of G. heterognathus-G. nystromi-G. catalinensis are clearly in need of further clarification.
Two species of Gnathophis are present in the Australasian region of which the only one known previous to this account is G. habenatus (Richardson, G. habenatus inhabits the shallow waters of harbours and river mouths from New Zealand to Lord Howe Island, New South Wales, Victoria, Tasmania, West Australia and possibly St. Paul's Island, South Indian Ocean, and is redescribed in this paper.
Ramsay & Ogilby (Congromuraena longicauda which has been accepted of recent years to be a subspecies of G. habenatus. Dr J. C. Yaldwyn, of the Australian Museum, Sydney, has kindly re-examined the type specimen of G. habenatus longicaudatus (Aust. Mus. regd. no. 1.1618) and informs me that, although the specimen is in poor condition with the caudal tip detached, a total of not more than 123 vertebrae are present. Two more specimens, Aust. Mus. regd. nos. IA.4984 (Karuah River Mouth, N.S.W., 14/6/G. habenatus from New Zealand. The Australian subspecies thus appears to be valid, although there is some little evidence to support the belief that differing conditions or duration of larval development in G. habenatus may affect the ultimate length of the tail in the adult. This matter will be discussed in greater detail below.
During the preliminary sorting of over 200 gnathophid leptocephali described elsewhere in this paper two groups of larvae emerged from the sorting, one having 116–131 myomeres, the other with 134–150 myomeres, both of which were otherwise closely similar. The group with the lower number of segments were readily identified with Gnathophis habenatus (120–129 vertebrae), but the second group was referable to no known adult. The abundance of larvae in this group suggested that the adult had been previously confused with G. habenatus. This subsequently proved to be the case as a close examination of the available New Zealand specimens of G. habenatus revealed the second species with vertebrae numbering 139–147, a longer tail, minute epidermal papillae, anterior nostril with a simple free flap and a round premaxillary-ethmoid patch of teeth extending conspicuously in advance of the maxillary patches. This species is known from rather deeper water than is G. habenatus, from New Zealand as far north as the Kermadec Islands.
The number of myomeres in leptocephali identified with Congermuraena mystax from the Atlantic (132–147) is almost identical with the known range for the second species in New Zealand waters (134–150). Having regard only to this and to the proposal that C. mystax is a Gnathophis would suggest that C. mystax may prove to be a species of the widest distribution, including New Zealand. Until the generic relationships of the Atlantic species are clarified, the present author feels justified in separating the second New Zealand species of Gnathophis from Congermuraena mystax.
Gnathophis habenatus habenatus (Richardson,
Material Examined. One specimen: gravid female, 275.5mm total length; Shelly Bay, Wellington Harbour; beach seine; Admiral; Orion;
Description. Proportional measurements (in per cent of total length) and counts from the above 23 specimens: total length 142.7mm-429.5mm, standard 98.4–99.2, head 14.8–19.3, snout 3.5–5.1, eye 2.5–4.8, interorbital 1.9–3.4, cleft of mouth 4.6–6.9, postorbital 8.5–9.5, branchial aperture 1.9–2.9, branchial interspace 3.3–6.4, pectoral 3.5–6.9, snout-vent 40.9–45.5, preanal 41.6–46.6, predorsal 17.2–20.0, depth just before eye 3.7–5.1, depth at pectoral origin 5.3–7.3, depth at anal origin 4.9–6.5, depth at midpoint of caudal region 3.8–4.7. Pectoral rays 12–13, dorsal rays before level of vent 43–55, dorsal rays 180–224, anal rays 129–160, caudal rays 5+4, lateral line pores before level of vent 33–38, vertebrae 120–127.
A small but robust eel with a body which is rounded in section especially along the trunk, with prominent myomeres and with the vent placed only a little in advance of the midpoint of the body. The head is depressed, with a sharp snout, underslung mouth, large eye, and the throat is thrown into many folds of skin. The fins are conspicuous and the caudal is noticeably rounded and abbreviated. Live specimens are very active animals, escaping easily from all but the finest mesh, and are strikingly coloured sliver to silver-bronze on the anterior part of the body with a brilliant silver iris.
Head sharply conical, depressed anteriorly, relatively long, contained about 6.5 times in total length but poorly differentiated from the trunk, the throat swollen in some individuals but nearly always thrown into narrow longitudinal folds which curve up around branchial region; snout sharp, bony, its length contained about 3.5 times in head, always projecting in advance of tip of lower jaw by just less than diameter of pupil; lower jaw rounded in ventral view, rather shovel-like, slender; mouth subterminal, oblique, with cleft of mouth extending to level of anterior margin of pupil and contained about 3.0 in head; upper lip weak, but limits of maxilla clearly distinguishable on side of snout; lower lip thick, fleshy, overlapping side of lower jaw; tongue well-developed, pointed, extending forwards to a point level with anterior margin of posterior nostril.
Teeth comparatively small, but larger on the shaft of the vomer than on the other dentigerous bones, sharply conical and closely packed except those on the shaft of the vomer where they are rounded and more widely spaced. Maxillary teeth in a broad band of about four longitudinal rows anteriorly of about 38 teeth each with the teeth slightly smaller anteriorly than posteriorly and more rounded medially than laterally. Premaxillary-ethmoid teeth small, about 20 in number, in an inconspicuous, broadly triangular patch which does not project much in advance of maxillary bands. Vomerine teeth clearly separated from those of the premaxillary-ethmoid patch and in a long, cigar-shaped band extending to a level two-thirds of the way along the maxillary bands; the teeth small and acute on the head of the vomer but larger, rounded and molariform on the shaft and in about five longitudinal rows of about 15 teeth at the broadest point of the patch. Teeth on the dentary similar in number, size and distribution to those of the maxillary bands.
Anterior nostril small, subterminal, placed on the ventral surface of snout just in advance of premaxillary-ethmoid patch of teeth. On superficial examination the nostril appears to be subtubular with the tube directed anteroventrally to ventrally; on closer examination the tube is found to have a scroll-like rim with an anterior free flap (see text-fig. 1, E). Posterior nostril inconspicuous, slit-like, placed just in advance of eye, level with horizontal diameter and with a simple, raised rim but no external tube. Eye subcircular to oval, large, contained about three times in postorbital; fleshy interorbital narrow, less than eye. Branchial aperture lateral, having a concave free edge, oblique, with lower extremity a little posterior to upper, which is slightly below middle of pectoral base. Vent usually protruding into profile, especially in gravid females.
Dorsal and anal fins delicate in life, although fleshy in preservative; caudal fin with the rays relatively short and the tip of fin rounded so that the fin forms a burrowing tip to the body. Pectoral fin elongate-oval in shape with its posterior margin rounded, originating clearly above midlateral level with the base oblique and the fin directed more or less posteriorly; a little longer than snout.
Lateral line conspicuous but scarcely raised above surface of trunk, originating very high on head, descending to meet midlateral level just posterior to level of vent but fading out at extreme posterior tip of tail. Cephalic sensory pores few, restricted to one occipital pore which occasionally has a small pore lateral to it, two or three postorbital pores, two inconspicuous but larger pores on the ventral aspect of opercular region, four to five minute pores along dentary and two pairs of small pores on ventral aspect of snout; of these the first pore lies medially to the base of the anterior nostril, the second in advance of it on the extreme ventral tip of snout. A pair of inconspicuous slit-like openings of the mucous cavities of the snout are present on the anterodorsal tip of snout. There are no discernible minute papillae on the head or above lateral line.
Colour in life olive-grey posterior to vent and above lateral line from level of pectoral base to vent; side of trunk conspicuously silvery-olive but becoming creamy-white ventrally; opercular region bright silver to silver-bronze; branchiostegal region pink; iris very brightly silver tinged with gold with crescentic dorsal and ventral black patches; dorsal and posterior part of anal fins with a relatively narrow black edging which becomes wider around caudal fin; caudal pink in some specimens; fin-rays pigmented with minute black spots. The bright silver colour and the prominent myomeres showing through the skin are unmistakeable features of this eel.
Remarks. Griffin (Gnathophis habenatus habenatus. Although Griffin gives a vertebral count of 44 + 78 for the New Zealand species this has probably been taken from Waite (G. habenatus longicaudatus, most unlikely for the Manukau examples, or (b) they have been confused with the new species of Gnathophis described below in which the vertebrae number 139–147, but in which the preanal length is short, ranging from 37.8% to 41.0% of total length, more likely for the Manukau examples especially since the new species is more abundant in the northern waters.
Griffin's figures of the tooth pattern in his specimens are not helpful, since the number of teeth on the vomer is far greater than ever observed by the present author; in addition, the toothed area on the dentary as shown is much wider than usual and there is an abnormal amount of variation in the size of teeth on various parts of the dentigerous surfaces.
G. habenatus habenatus is occasionally captured in shallow trawls along the New Zealand coast, mainly in Cook Strait and south of it, but its more frequent locality is Wellington Harbour. Indeed, although Richardson gives as the type locality "Cook's Strait" it is likely that his specimen came from Wellington Harbour where H.M.S. Erebus and H.M.S. Terror spent some days. From March to June the species is abundant in Wellington Harbour although it can only be captured using a very fine mesh seine net and sufficient hauling rope to enable the net to work over the green-grey mud some distance from the shore in which the eels are possibly buried during the day. These eels are more easily captured in the early or late evenings when the tide is at its lowest. An indication of the abundance of this species in Wellington Harbour during the early winter is shown by one haul on G. habenatus habenatus collected from this area contained crustaceans and polychaetes but these were always too far digested to be identified.
The majority of specimens collected from Wellington Harbour over a period of years appear to be close to spawning, the females having relatively large eggs of about 1.0mm or more diameter, the males having well-developed testes. Some of the females on capture were so gravid that the abdomen was greatly swollen and slight pressure caused large numbers of ova to be extruded (pers. comm. by Mr J. M. Moreland, Dominion Museum, Wellington). In eight specimens collected in Conger myriaster (Brevoort) and Muraenesox cinereus (Forskål) by Takai (
The abundance of near-spawning individuals of both sexes of G. habenatus habenatus in Wellington Harbour may indicate that the eels are assembling preparatory to breeding. The species appears to be absent from the harbour during middle spring to late summer. No young stages of any eels have been collected from Wellington Harbour plankton despite regular weekly collections over two years from an area adjacent to Evans Bay where many of the adult eels have been seined. It is now known from the study of a large collection of leptocephali of G. habenatus from eastern Australian waters that this species must spawn some distance off the New South Wales coast over the continental shelf with the adults living in the estuaries and the shallow coastal waters. This pattern may also be true of the New Zealand population and indeed the fully-gravid condition of the specimens collected in Wellington Harbour suggests that the spawning area cannot be far off the New Zealand coast.
Only five leptocephali of G. habenatus have been taken from New Zealand, one on the west coast of the South Island, the remainder from the Cook Strait area. All of these are advanced in development and three appear to be under-going
G. habenatus have been made available to the author in this study and an account of the larval development of this species is given below. As indicated above, G. habenatus is spawning off the New South Wales coast and the leptocephali are transported to the Tasmanian and New Caledonia areas. It is possible that the larvae of this species are transported further to the New Zealand region giving rise to what is known as G. habenatus habenatus. The shorter tail in this subspecies may be due to a prolonged pelagic life of the leptocephali. There is always the remote possibility that spawning of New Zealand individuals does not take place, or if it does the young perish at an early age due to inadequate or unfavourable environmental conditions.
Material Examined. C.S.I.R.O. Division of Fisheries and Oceanography (Cronulla) Collection (85 specimens,: 5.5mm total length, 7.0, ca. 10.0, 10.8, ca. 12.0, Warreen Station 3/40, 32° 47′ S., 152° 40′ E, Discovery St 2724, 34° 05′ S., 151° 29′ E, Warreen St 132/39, 30° 15′ S., 153° 33′ E., Discovery St 2723, 34° 08′ S., 151° 33′ E, Warreen St unknown, ca. 34° 04′ S., 151° 15′ E., ?/39, no other data; 15.0, St 40/39, 35° 06′ S., 150° 51′ E, Discovery St 2718, 33° 55′ S., 153° 02′ E., Warreen St 27/40, 31° 08′ S., 153° 05′ E., Derwent Hunter St 16/52, Port Fairy wide, Warreen St 224/39, 35° 03′ S., 151° 09′ E, Discovery St 2710, 37° 06′ S, 150° 48′ E., Warreen St 36/48, 28° 48′ S., 113° 47′ E
Australian Museum Collection (7 specimens,: ca. 69.0, Aust. Mus. regd. no. IB.3786, Budgewoi Beach, N.S.W.,
Western Australian Museum Collection (89 specimens,: Egg with developing prelarva, Accession No. P5306, Lancelin, 37 miles west of West End, Rottnest Island, Western Australia,
Since this paper was written the following additional 36 specimens became available: 59.5, P5535, 22mls,
Centre d'Océanographie de l'Institut Français d'Océanie Collection (5 specimens,: 60.4, IFO Station P As 8, 23° 01′ S., 158° 05′ E.,
New Zealand Collections (5 specimens,: 98.0, VUW Zoo. Dept. Coll., probably Cook Strait, no other data; 111.1, Dom. Mus. No.
Description. 191 specimens: total lengths 5.5mm-138mm, myomeres ca. 116–131, dorsal fin-rays 121–215, anal fin-rays 96–173. Description made from a specimen which has just begun metamorphosis, DFO (Cronulla) Coll. Warreen St 36/48 (measurements in mm) : total length 90.4, head 4.6, snout 1.5, eye 1.0, upper jaw 1.9, postorbital 2.4, branchial aperture 0.6, pectoral 1.1, snout-vent 79.2, predorsal 68.3, depth just before eye 1.9, depth at pectoral origin 3.6, depth at midpoint between pectoral and vent 10.5, depth at anal origin 7.1. Branchiostegal
and pectoral rays not formed, dorsal rays before level of vent 109, total dorsal rays 163, anal rays 136, caudal rays 5 + 4. Teeth . Myomeres 97 + 26 = 123. a–d = 33. Vertical vessels at 12, 37, 41. Anterior margin of gall-bladder at 37.
Body relatively elongate, much compressed except along the head, not deep, the maximum depth 8.5 in total length, reducing more gradually in front of the midpoint. Head short, about 19 in total, distinct from trunk; snout sharply conical, about one-third of head, its dorsal profile barely convex; anterior nostril a short tube directed forwards, with a simple rim; posterior nostril widely open,
Anguilla but directed a little more anteriorly; branchial aperture small, barely curved. Pectoral fin short, a little less than twice in postorbital, with a thick, fleshy base but a thin web; fin-rays not sufficiently well-developed to be counted. Dorsal fin low but with a distinct anterior margin over the 64th myomere. Anal fin similar but with the basal structures not so well developed. Caudal fin conspicuous, partly separated from posterior tips of dorsal and anal fins.
Pigmentation in formalin in the form of a minute, black, crescentic patch on the anterodorsal aspect of the eyeball and a larger, conspicuous brown to black patch below the posteroventral margin of the iris; a series of three round melanophores on each side of the throat, each with a compact, central dark area and a lighter surrounding area; a paired ventral somatic series of about 95 rounded melanophores following the course of the intestine from the ninth segment, thence on each segment to the vent; a series of minute, stellate, more diffuse melanophores on the bases of the anal fin-rays with an average of about two spots for every three rays; a row of darker, more conspicuous spots on the tips of the hypurals; a few spots on the bases of the terminal dorsal rays; a few deep spots on the posterior part of the spinal cord and vertebral column.
Vertical blood-vessels to the intestine numerous, occurring at segments 12, 20, 23, 27, 29, 31, 37, 41, but of these only those at 12, 37 and 41 are conspicuous. Gall-bladder easily seen, its anterior margin at myomere 37.
Remarks. Whitley (Gnathophis habenatus longicaudatus. I have examined this specimen and find that it agrees well with Whitley's description but that it is a typical muraenid leptocephalus showing little similarity other than in number of myomeres to the larvae of G. habenatus. It has a short head, no pectoral, a rounded tail and pigment in a series of minute, rounded spots ventral to the gut anterior to the gall-bladder but dorsal to the gut between the gall-bladder and the vent, with pigment spots on the jaws, branchial region and occiput. There is no crescentic black patch below the iris and the eye is round, not oval. The Maroubra specimen is described by Whitley as agreeing in myomere number, 127, with a practically metamorphosed specimen of G. habenatus longicaudatus from Cape Everard, Victoria (Aust. Mus. regd. no. IA.6263). The Maroubra specimen does not now have a silver iris, a characteristic feature of late Gnathophis larvae, but this may have faded. As I have yet to examine in detail the muraenid leptocephali from the east Australian area I cannot finally identify this specimen, but there is little doubt that it belongs to the Muraenidae. The Cape Everard specimen, which I have not seen, is quite probably referable to G. habenatus longicaudatus in view of its area of capture.
Although there are otherwise no observable morphological differences between leptocephali of G. habenatus collected from western Australia through to eastern Australia, New Caledonia and New Zealand, there are slight differences in the average number of myomeres in each group. Text-fig. 3 shows that east Australian larvae have slightly more numerous myomeres than do those from the west and also New Zealand adults of G. habenatus habenatus, the average numbers being 125.6, 122.3 and 123.2 respectively. The five New Caledonia larvae have an average of 126.6 myomeres and are therefore included in the east Australian group. The differences shown may indicate three distinct populations, one spawning off west Australia, one off New South Wales, and one in New
G. habenatus habenatus from Wellington Harbour.
Dakin & Colefax (
A number of leptocephali have been described from other parts of the world which bear at least superficial resemblances to those of G. habenatus. The best known of these is L. Congermuraena mystax from the central and southern Atlantic Ocean. Except for the absence of the minute crescentic patch of black pigment above the eye (which in any case may easily be overlooked) and the greater number of myomeres (132–147) this species is strikingly similar in form and pigmentation to the leptocephali of G. habenatus. Lea's description (Congermuraena mystax (Delaroche) is a Gnathophis. Leptocephali of this genus are readily distinguishable from those of Ariosoma which have pigment present on the lateral surface before the lateral line on each myoseptum, a round eve and more numerous ventral spots; from those of the deep-water genus Pseudoxeno-mystax which have a relatively deep body, a round eye without black pigment below the iris and pigment on the anal bases; and from Conger which may have large spots on the lateral surface but always possesses distinct spots above the anal fin.
Indo-Pacific congrid leptocephali of the Gnathophis group are otherwise known only from several species described from the Pacific coast of Central America. Leptocephalus cingulus (Garman, G. catalinensis; the absence of ventral pigment has been observed in specimens of L. Gnathophis habenatus which have been preserved for some years in formalin. Leptocephalus cinctus (Garman, L. Congermuraena mystax has 138 myomeres and a silver iris and may also be referable to G. catalinensis, but this is known from one specimen and there is no record of the range of vertebrae in this species. L. dentatus (Garman, L. obtusus (Garman, Gnathophis group of leptocephali. They are probably larvae of Ariosoma gilberti (Ogilby,
Growth and Metamorphosis (Text-figs. 4, 5, A-E). The 191 leptocephali of Gnathophis habenatus examined in the preparation of the above description range in total length from 5.5mm to 138.2mm. The collections include one egg with an almost completely developed embryo. About 150 of these specimens are leptocephali in various stages of metamorphosis in which the vent is in the process of movement towards its final position in the elver and the body undergoing contraction in length. Included in the latter group are two almost metamorphosed glass-eels, that is, elvers which have the general form of the adult and still have the pigment of the leptocephali. The material examined is sufficient, therefore, to give a very good indication of the morphological changes taking place during
(a) Myomere Shape. At a length of below 10.0mm the myomeres are shallow V-shaped with the dorsal and ventral limbs of the future W-shaped myomere only just appearing in the myomeres at the middle of the body length. Post-anal myomeres have at best only a very slight V-shaped flexure. The tendency for the V to deepen and become W-shaped increases steadily until at about 40mm total length all myomeres are W-shaped, although the post-anal segments have very short dorsal and ventral limbs.
(b) Number of Preanal Myomeres (Text-fig. 4). During growth from about 5mm to 30mm in total length the vent undergoes a rapid actual movement from a position located at about myomere 55 posteriorly to myomere 100 in a total of about 125. The vent remains in this relative position until the total length reaches about 80mm when in most cases metamorphosis begins. There is then a rapid reduction in the length of the gut so that the vent moves forwards (or regresses) to reach a final position in the elver at about the 37th myomere. This movement is illustrated for the 154 specimens in Text-fig. 4. To eliminate as wide a variation as possible in the plot of preanal myomeres against total length due to variation in the total number of myomeres the number of preanal myomeres in each specimen was reduced to a percentage of the total number. It was also found that a plot of preanal length against total length produced a much wider scatter due to the relatively large errors made in measuring the preanal lengths especially of the smaller specimens, since these often could not be laid very flat and they were easily stretched beyond their normal lengths. It is important to note that, as the change in the number of preanal myomeres shows, there is an actual movement of the vent at first posteriorly and then after metamorphosis begins, anteriorly. This method of analysis eliminates the factors of differential growth rates of the preanal region or of the tail. As Text-fig. 4 shows, there is a great variation in the size of the leptocephalus at which metamorphosis begins. The usual length of the body at the onset of metamorphosis is between 70mm and 90mm, but many larvae reach much greater lengths without sign of metamorphosis. The significance of the latter is discussed in greater detail below.
(c) Number of Dorsal and Anal Fin-rays. The dorsal fin-rays begin to differentiate so that their basal structures are sufficiently well developed to be counted at a total length of about 37.0mm. At this length the difference between the dorsal and anal origins is about 25 complete myomeres and throughout growth and metamorphosis the dorsal origin advances towards its final position above the middle of the pectoral at about the same rate as the advance of the vent. The anal rays do not differentiate until the body length is about 55mm, when they number about 120. There is a slow increase in the number of dorsal and anal fin-rays to their final numbers of about 180 and 140 respectively. Longer leptocephali, showing little sign of normal metamorphosis, have a greater number of dorsal fin-rays, about 205–210.
(d) Teeth (Text-fig. 5). At a length of about 5mm the larva has 2–3 very acute teeth on the upper jaw, of which the first is long, needle-like, curved slightly downwards but generally directed forwards. On the lower jaw there are also 2–3 similar teeth, the first of which is directed anterodorsally. The lower teeth always project outside the upper and are usually fewer in number during all stages of development. At 20mm total length the upper teeth number about 5,
Anguilla, there is a minute, needle-like tooth on the dorsal surface of the snout, directed anteriorly, immediately above the most anterior tooth. As growth proceeds, the bases of the larval teeth become overgrown by the fleshy snout and the teeth appear to be shorter in later leptocephali. As the metamorphosing leptocephalus takes on the appearance of the elver the larval teeth are progressively lost, from the anterior part of the jaws posteriorly.
(e) Nasal Organ (Text-fig. 5). Until about 40mm total length the nasal organ has a single wide opening with a slightly raised rim. The upper and lower margins later grow together at the midpoint of this opening to form the two nostrils. The anterior nostril becomes tubular but remains with a simple rim until well after metamorphosis of the elver, when the scroll-like condition develops. The posterior nostril remains widely open until the elver, when it narrows to form a slit.
(f) Pigmentation (Text-fig. 5). Changes in pigmentation are the most conspicuous changes in the development of the larva. The early leptocephalus at 5mm total length shows pigment in the characteristic somatic ventral series as about six rather irregularly-spaced, rounded spots beginning at the level of the 20th segment. There are one or two minute black spots on the ventral surface of the lower jaw and a few minute specks of black pigment above the caudal tip. A larva of 10mm shows an increase in the number of ventral spots to about 12; there are two or three spots on the lower jaw and there has been an increase in the caudal pigment to a short dorsal line of spots and a few ventral flecks. At 20mm there are about 18 ventral spots, 4–5 spots on the lower jaw and a wide scattering of pigment on the caudal fin. At about the time when the posterior movement of the vent has ceased the pigment on the lower jaw and caudal region has disappeared and there remain about 30–40 spots in the ventral series. At this time, however, a small crescentic patch of pigment appears below the iris. This is retained throughout the metamorphosis to the juvenile eel. At about 70mm-80mm in length the ventral series consists of about 45 spots beginning at about the 10th segment; there are 1–3 round spots on the throat on each side of the heart; pigment has appeared on the bases of the anal rays, deep on the ends of the hypurals, on the posterior dorsal rays and on the posterior tip of the vertebral column. Metamorphosis then rapidly takes place, and although the throat pigment is lost the ventral series is retained until the end of the metamorphosis as are the spots on the bases of the anal rays. In some of the larger leptocephali of 120mm or more a second row of spots develops internal to the first row. Just after the beginning of metamorphosis the silver iris pigment, which is so characteristic of the adult eel, develops but the black pigment above and below the iris is retained. Late metamorphosing leptocephali or glass-eels show a short line of very closely-packed spots on each side of the vent, which is perhaps due to the telescoping of the posterior part of the ventral series as the vent regresses (Text-fig. 2, F).
(g) Other Changes. At the end of the period during which there is an active movement of the vent posteriorly the caudal fin begins to differentiate from the tips of the dorsal and anal fins to form a distinct caudal fan. This is carried to the extreme in the elver, which, in common with the elvers of Anguilla, have a broad caudal fin (Text-fig. 2, D). There is no observable change in the relative
Geographical Range and Location of the Spawning Areas. The 155 larvae have a wide geographical range. A total of 90 specimens were collected from the eastern Australian coast between latitudes of about 24° S. and 43° S.—i.e., from the middle of the Queensland coast to Maria Island, Tasmania, and off Port Fairy, Victoria; 92 specimens were collected from Western Australia from 29°S. to 32° S.; 5 specimens from the New Caledonia region between the South Bellona Reef and Nouméa; 5 specimens from New Zealand consisting of one from the west coast of the South Island and the remainder from the Cook Strait region. Leptocephali of Gnathophis habenatus therefore appear to be more numerous in the areas relatively close to the western and eastern coasts of Australia in latitudes between 24° S. and 43° S. This does not reflect more frequent trawling in these areas since the waters of the New Caledonia region have been examined extensively in the years G. habenatus in these collections. The New Zealand region has been by no means ignored by institutions working this area, but the only specimens of this species collected have been occasional beachcast individuals.
In the eastern Australia-New Caledonia-New Zealand area the smallest leptocephali were collected from a locality some 20 miles from the New South Wales coast over the continental slope near the latitude of Sydney. The largest leptocephali were collected on the periphery of the area of distribution, but in general no simple pattern of increasing size towards the periphery is shown in these collections. Text-fig. 5 shows in greater detail the distribution of this group of 100 specimens. The indications are that the spawning area for eastern Australian G. habenatus is very likely to be off the New South Wales coast. The large variation in the total lengths of leptocephali collected at a number of stations would suggest spawnings at different times and that a few larvae may remain in the same area for some time, possibly as a result of countercurrents. The northward range of leptocephali along the Queensland coast and out to New Caledonia suggests that the leptocephali are not completely dependent upon the East Australian Current for their movement, and it is probable that countercurrents are important in the dispersal of the larvae.
As shown in Text-fig. 4, metamorphosis begins in most specimens at about 70mm-90mm total length. However, a few specimens in the collection are much larger than this, reaching 138.2mm. This greater length occurs only in specimens which were collected far from the indicated spawning area. For example, the five Cronulla specimens of greater length than 90mm were all collected from the coast of Victoria to Maria Island, Tasmania; one other large specimen was taken from near Nouméa, and the five New Zealand specimens are all larger than most specimens beginning metamorphosis on the Australian coast. On the other hand, four of the seven Australian Museum specimens beachcast near Sydney—that is, close to the spawning area, are all at stages in metamorphosis at a size which is less than all other metamorphosing specimens.
The geographical range of the material from Western Australia is more restricted than that from eastern Australia. The smallest specimens amongst these 92 larvae is an egg with its developing prelava taken from a position located 37 miles west of Rottnest Island in 37 metres; the largest specimen measures 110.5mm and is undergoing metamorphosis. There are two glass-eels in this collection, one
G. habenatus is also spawning off the coast of Western Australia as well as off the east coast, probably in the area west of Rottnest Island over the continental slope.
The eastern Australian collection contains only a few metamorphosing individuals and was made over a considerable area. The western Australian collection, made over a much smaller area, contains nearly one-half as metamorphosing larvae. This latter collection includes specimens which cover essentially the same size-range as the eastern Australian material excepting the few larger larvae from the furthest limits of the distribution of the latter. In both collections metamorphosis appears at a length of some 80mm, which accordingly can be regarded as the usual or normal size for metamorphosis indicating perhaps that the process is physiological and endogenous. In contrast, there are the larger metamorphosing larvae in the eastern Australian collections, of extreme size in the New Zealand collections and rare in the western Australian collections.
If the stimulus to metamorphosis is entirely endogenous, the few largest larvae may be consequent from individual irregularities in the time of onset of the process. Such individuals, because of their relatively low numbers associated with a "faulty" mechanism for metamorphosis, would not ordinarily be regarded as providing or maintaining a population of adults. The absence as yet of adults from New Caledonia and northern Queensland, supports the idea of a failure to complete normal metamorphosis.
The relative abundance of the species in New Zealand with knowledge only of large metamorphosing larvae on our coasts, suggests that a postponement of metamorphosis to sizes well above 90mm to 100mm may well be normal. Setting aside the question of a subspecific distinction in this matter (relating to the difference in preanal lengths in the adults of G. habenatus habenatus and G. h. longicaudatus, there remains the probability that the mechanism of metamorphosis is endogenous but subject to retardation in operation, a retardation dependent on an environmental control. The demonstration of adults at the extremes of the larval distribution to the north in Australia and New Caledonia and large collections of larvae for the New Zealand area are required before further analysis of the possible mechanism can be undertaken.
It has been shown that New Zealand specimens of G. habenatus differ from Australian specimens in having a slightly greater preanal length in the adult as well as slightly fewer vertebrae. If metamorphosis has been delayed by a prolonged larval life to produce a longer larva it is possible that this would have an effect on the morphological characters of the adult. This has already been shown for Conger myriaster by Takai (G. habenatus longicaudatus then the amount of regression of the vent would be relatively greater. The vent may only be capable of a certain degree of regression for morphological reasons (although I can suggest no such specific reason) and the adult would have a relatively long preanal length, as in the New Zealand G. habenatus habenatus.
Bathymetric Distribution. Many of the hauls in which leptocephali of G. habenatus were collected were oblique or vertical and a precise depth range is therefore not available. The hauls ranged from the surface to 730m, but the majority of specimens were taken in depths ranging from the surface to 200m. The species appears to be most abundant in about 50m-100m in common with the larvae of many species of eels.
Poutawa habenata (Richardson). Griffin (partim), Trans, roy. Soc. N.Z., 66: 16.
Material Examined. Type specimen: gravid female, 445.0mm total length; Kaikoura coast in 40–50 fathoms; commercial otter trawl;
Description. Proportional measurements (in per cent total length) and counts from the type and the four paratypes (in parentheses): standard length 98.8 (98.4–98.9), head 15.5 (15.1–16.6), snout 4.4 (4.4–4.7), eye 2.7 (3.1–3.5), interorbital 1.8 (1.9–2.6), cleft of mouth 5.9 (5.8–6.6), postorbital 7.9 (7.8–8.2), branchial aperture 1.8 (1.5–1.8), branchial interspace 4.8 (3.0–3.4), pectoral 4.7 (4.7–6.0), snout-vent 38.4 (37.5–37.9), preanal 41.0 (37.8–39.6), predorsal 16.9 (16.9–17.6), depth just before eye 3.8 (3.1–4.3), depth at pectoral origin 5.6 (4.8–5.3), depth at anal origin 5.5 (4.3–5.2), depth at midpoint of caudal region 3.4 (3.1–3.6). Pectoral rays 13 (12–13), dorsal rays before level of vent 41 40–56), dorsal rays 211 (210–227), anal rays 160 (157–177), caudal rays 5+4 (5 + 4), lateral line pores before level of vent 37 (35–38), vertebrae 145 (139–147).
Body slender, not greatly elongate and little compressed, with prominent myomeres and the vent placed appreciably in front of the midpoint of the body. Head depressed with a sharp bony snout, inferior mouth and large eye. Median fins well-developed but delicate.
Head conical, relatively long, contained about 6.5 times in total length but not clearly differentiated from trunk; snout acutely pointed, bony, about 3.5 in head, projecting in advance of lower jaw by an amount equal to about half diameter of eye, usually a little less; lower jaw rounded in ventral view, slender; mouth conspicuously subterminal, moderately oblique, with cleft extending not beyond a point level with anterior edge of pupil and about three times in head length; upper lip weak, lower thick and fleshy; tongue well-developed.
Teeth generally small but larger on premaxillary-ethmoid than on other dentigerous bones, relatively sharp and conical except on the main part of the vomer, numerous, closely-packed to form broad bands. Maxillary teeth in about four or five longitudinal rows of about 35 teeth, those of the outer row slightly larger than the remainder and the dentigerous area expanding anteriorly with the teeth small and cardiform; a few of the teeth in the medial row molariform. Premaxillary-ethmoid teeth about 12 in number, conspicuous, in an oval patch broader than long, its length contained five times in the length of the vomerine patch; premaxillary-ethmoid teeth almost all exposed in front of the tip of the lower jaw; about a dozen much smaller teeth between this patch and the anterior extremity of the vomerine patch so that the two patches are almost confluent. Vomerine teeth in about three to five longitudinal rows of about 16 teeth each forming a cigar-shaped patch which is about three-fifths as long as the maxillary patch; the teeth large and rounded, short, molariform, more widely spaced than teeth on maxilla or dentary; about a dozen very small, sharp teeth at the anterior extremity of this patch almost in contact with those of the premaxillary-ethmoid patch. Teeth on the dentary similar in number, size and distribution to those on the maxilla although there are fewer minute teeth anteriorly; length of dentigerous area equal to total length of upper area including premaxillary-ethmoid patch, but tip of dentary level with tip of maxilla (not indicated in Text-fig. 7, F).
Anterior nostril small, subterminal, on ventral surface of snout level with anterior extremity of premaxillary-ethmoid patch of teeth; a short external tube with a small free flap so that the rim is not simple. Posterior nostril small, placed a little in advance of eye on a level slightly above the horizontal diameter; usually slit-like with a raised complete rim but no external tube. Eye circular to slightly oval, large, about three in postorbital; fleshy interorbital space narrow but difficult to determine accurately, usually considerably less than eye. Branchial aperture lateral with a concave free edge, slightly oblique, with the ventral extremity more posterior and with the dorsal extremity a little below middle of pectoral base,
Median fins delicate in life, rather fleshy on preservation, their posterior tips confluent with the caudal; rays clearly visible. Dorsal fin well-developed, its maximum height near level of vent, when fully extended contained about three times in body depth at level of vent; originating only slightly in advance of level of midpoint of pectoral fin; rays rather few compared with most other congrid eels. Anal fin a little less strongly developed than the dorsal, its maximum height on full extension about halfway along caudal region and about 3.5 in depth of body at vent. Caudal fin rounded and the rays relatively short, giving an impression that the tail is used for burrowing. Pectoral fin elongate-oval in shape, slender, originating slightly above mid-lateral level and directed somewhat posterodorsally, its length a little greater than snout.
Lateral line very conspicuous as a raised ridge, arising high up on head and reaching midlateral level just posterior to vent. Pores simple, not carried on the ends of short tubes, clearly visible except along the most posterior part of the caudal region. Cephalic sensory pores restricted to one occipital pore, five or six circumorbital pores, two opercular pores and a series along ventral aspect of lower jaw. Two small pores lie immediately in front of, and medial to, the anterior nostril on the ventral surface of the snout. An inconspicuous but long slit occurs dorsally on each side of snout tip. Several series of surface sensory organs, indicated by minute papillae, occur on the head and in a longitudinal row above the lateral line although the papillae of the latter series are sparse and widely spaced. The cephalic papillae are distributed in lines on the dorsal surface of the snout, behind eye, on lower jaw and in semicircular rows on operculum and in front of pectoral fin.
Colour in life olive-green over silver, with a silver iris; in preservative it is dark brown on dorsal aspect of head and above lateral line, lighter below, with the whole of the dorsal and the posterior part of the anal edged with a narrow black band.
Remarks. Gnathophis incognitus differs from G. habenatus in having 139–147 vertebrae, a small free flap on the anterior nostril (Text-fig. 7, E), premaxillary-ethmoid teeth in an oval patch of teeth which extends noticeably in front of the maxillary patches, numerous sensory papillae and pores on the head and body, a pointed pectoral fin, a lateral line which is rather more conspicuous as a raised ridge and a slightly longer caudal fin; the present species has only sparse molariform teeth on the medial aspects of the maxilla and dentary but more numerous minute, pointed teeth on the anterior parts of these bones than does G. habenatus. It is a more slender eel with a relatively short preanal region, usually less than 40% of the total length, and is duller in colouration. G. incognitus inhabits waters of about 30 fathoms to the edge of the continental shelf and appears to have a more northerly distribution in New Zealand than does G. habenatus habenatus.
G. incognitus resembles G. xenicus (Matsubara & Ochiai,
Material Examined. C.S.I.R.O. Division of Fisheries and Oceanography (Cronulla) Collection (45 specimens,: 5.3mm total length, Warreen Station 44/39, 34° 02′ S., 151° 15.5′ E, Discovery St 2723, 34° 08′ S., 151° 33′ E., Warreen St 139/39, 31° 51.5′ S., 152° 50′ E, Kywong, 18° 46′ S., 147° 15′ E, Keeper Reef, Great Barrier Reef, Discovery St. 2722, 34° 04′ S., 151° 50′ E., Warreen St 127/39, 33° 18′ S. 152° 13′ E., Derwent Hunter St DH 94/55, 42° 50′ S., 150° 50′ E., Warreen St 21.4/39, 36° 14′ S., 150° 25′ E., Discovery St 2709, 37° 06′ S, 150° 35′ E, Derwent Hunter St DH 80/53, Maria Island wide, Discovery St 2710, 37° 06′ S., 150° 48′ E.,
Australian Museum Collection (1 specimen): 135.1, Aust. Mus. regd. no. IA.2058, no other data.
Western Australian Museum Collection (3 specimens,: 44.2, Accession No. P5234, Lancelin, 46 miles west of West End, Rottnest Island, Western Australia,
Centre d'Océanographie de l'Institut Français d'Océanie Collection (15 specimens,: 22.7, IFO Station MWT 2, 10 miles west of the Bulari pass, off Nouméa, (Neothunnus macropterus, longlined at 21° 33′ S., 166° 32′ E.,
New Zealand Collections (3 specimens,: 126.0, Dom. Mus. No. 2131, Dom. Mus. St. 210, net 4, Bay of Plenty, Feb/57, cone-net, 400m; 132.0, Dom. Mus. No. 1771, beachcast at Lake Ferry outlet, Palliser Bay,
Description. 68 specimens: total lengths 5.3mm-143.2mm, myomeres 134–150, dorsal fin-rays 175–269, anal fin-rays 130–184. Vertical blood-vessels at 11, 37, 46. Anterior margin of gall-bladder at about myomere 37. a–d = ca. 33.
Remarks. Larvae of Gnathophis incognitus are very closely similar to those of G. habenatus but may be distinguished from the latter mainly in having a greater number of myomeres. Text-fig. 8 shows the number of myomeres in larvae of the two species. The greatest proportion of specimens of G. incognitus have 143 myomeres while G. habenatus has 123 and the ranges of the two species do not overlap. The two species are therefore easily distinguished on this character alone, but there are other features which separate the two.
G. incognitus has the last vertical blood-vessel at myomere 46 and preanal myomeres numbering about 112 during the major part of the growth period of the larva. This may be compared with G. habenatus, which has the last vessel at myomere 41 and the preanal myomeres numbering about 100. There are slightly more numerous dorsal and anal fin-rays in G. incognitus.
Some of the small larvae identified as G. incognitus may possibly be referable to species of Conger since at the time of writing there are no known characters which could be used to separate very young larvae of the two genera, Conger and Gnathophis. At this early stage the differences in pigmentation which are the major characters by which older larvae of the two genera are separated are insufficiently developed to be useful. Conger wilsoni (Bloch & Schneider, C. cinereus cinereus Rüppell,
Growth and Metamorphosis. Similar changes in shape of myomeres, number of preanal myomeres, number and distribution of teeth, etc., and distribution of pigment take place in the growth of leptocephali of G. incognitus as already described for G. habenatus. The 68 specimens range in total lengths from 5.3mm to 143.2mm. Text-fig. 9 shows that during the earlier stages of growth from loss of the yolk-sac at about 5mm to a length of 30mm there is a rapid increase in the number of preanal myomeres from 35% to 80% of the total. There are insufficient larvae in stages of metamorphosis to state when this normally takes place in G. incognitus although one specimen from New Caledonia at 82.7mm total length has preanal myomeres about 55% of the total, indicating that metamorphosis is well under way. On the other hand, many of the other late larvae are at the same stage of metamorphosis at a total length of about 120mm-130mm. The larvae of this species appear to reach a greater maximum size than do those of G. habenatus, there being 12 specimens over
G. habenatus. Three early elvers of G. incognitus, total lengths 70.0mm, 80.1mm and 84.3mm from the Kermadec Islands by their colouration have evidently just undergone metamorphosis. The late glass-eel of G. habenatus from Western Australia already described is 61.2mm total length so it is possible that G. incognitus indeed has larger leptocephali and elvers.
Geographical Range and Location of the Spawning Areas. The 68 larvae of G. incognitus were collected from about the same area as were those of G. habenatus. A total of 46 of these larvae were collected on the east Australian coast mainly between 20° S. and 40° S. along the New South Wales coast and off Tasmania with a single specimen from the Great Barrier Reef, North Queensland. Fifteen larvae were taken off New Caledonia; three larvae were collected in the New Zealand region; but only three specimens were collected off the west Australian coast. The smallest leptocephali were taken from the same general locality off the New South Wales coast as were the smallest larvae of G. habenatus, while the largest were taken again on the periphery of the area of distribution—that is, from Tasmania to New Zealand. However, like G. habenatus, a number of the larger leptocephali were collected with the smaller larvae off New South Wales. Spawning of this species would therefore appear to take place in about the same area off eastern Australia as does G. habenatus. However, compared with the latter species there would seem to be two differences in distribution of G. incognitus (a) larvae are more abundant in the New Caledonia region, (b) larvae are much less abundant, even rare, off Western Australia, although a limited spawning probably takes place here also.
Bathymetric Distribution. No precise figures are available for the depths at which the leptocephali of G. incognitus are more abundant, but the range of depths of the tows in which this species were collected is 0m-400m with the larvae more frequent in 50m-100m.