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Deep-Water Eels from Cook Strait, New Zealand
Systematic Account — Family Nemichthyidae
Systematic Account
Family Nemichthyidae
Naked deep-sea eels with the body extremely slender and jaws excessively attenuated; snout much more than half length of head; teeth small with backwardly-directed, curving lips, numerous, set in curving bands and quincunxial rows; two pairs of large nostrils, the anterior with a short tube, close in front of eye; nuchal constriction present; gill-openings well developed, convergent forward, anus far in advance of middle of length; pectorals and vertical fins well developed; fin membranes thin, not enveloping rays; lateral line pores present or absent; caudal filament present or absent.—Beebe and Crane, 1937b, p. 350.
The members of this widely distributed family are delicate, attenuated eels living the major part of their lives in mid-water depths. Roule and Bertin (1929, pp. 1–113) and Beebe and Crane (1937b, pp. 349–383) have added greatly to the knowledge of this family and in particular Nemichthys scolopaceus Richardson, 1848 and Borodinula infans (Günther, 1878). Less frequently recorded species of these genera, especially those from the Pacific region, are not well known.
Previous to this account the Nemichthyidae has been recorded only once from New Zealand waters; this was the occurrence of a damaged specimen of Nemichthys on a baleen plate of a humpback whale killed near Tory Channel, Cook Strait, in July, 1952. The specimen retained sufficient character in spite of its damaged condition to be referrable to N. scolopaceus. In their description of the specimen, Richardson and Garrick (1953, p. 467) are of the opinion that the eel had been page 4
taken by the whale at a depth between 50 and 100 fathoms. The genera of the family are well characterized. Günther (1878, p. 251) originally included all known snipe-eels in the genus Nemichthys but Gill and Ryder (1883, p. 26) later divided this genus into two sections, Nemichthys and Labichthys, mainly on the nature of the lateral line—a triple row of pores in the former and a single row in the latter. It was further recognised by Jordan and Davis (1891, p. 655) that Labichthys could be divided into those forms in which the "ano-pectoral length" is very short, equal to only about 0.7 of the postorbital length, and those in which this was much greater, equal to five times the postorbital length. The forms so recognised were named Labichthys and Avocettina respectively. Whitley (1931, p. 334) has rejected the generic name Avocettina, this being preoccupied by Avocettina (pro- nus Bonaparte, 1850), Mulsant and Verreaux, 1866, Aves, in favour of Borodinula, and this is accepted in the following account.
Borodinula Whitley, 1931
Nemichthys Günther, 1878 (partim). Ann. Mag. Nat. Hist., 5 (2): 251.
Labichthys Gill and Ryder, 1883 (partim). Proc. U.S. Nat. Mus., 6: 26.
Avocettina Jordan and Davis, 1891. Rep. U.S. Comm. Fish. (1888), 16: 655.
Borodinula Whitley, 1931. Aust. Zool., 6 (4): 334.
Nemichthyids with a single row of pores in the lateral line and the anus located far behind the level of the pectoral base; caudal filament absent, teeth quincunxially arranged in straight rows; dorsal origin immediately behind level of pectoral base; dorsal rays in middle third of body neither short nor spinous.—Beebe and Crane, 1937b, p. 366.
Four species of Borodinula are recognised. B. infans (Günther, 1878), is cosmopolitan in distribution; B. exophthalma (Parr, 1932) is known from the Atlantic; the remaining two, B. gilli (Bean, 1890) and B. bowersii (Garman, 1899) are restricted to the Pacific. Of these species, B. infans was shown by Roule and Bertin (1929, pp. 26–28) to be a widely variable form possibly divisible into more than one species. These authors also synonymised B. gilli and possibly B. bowersii with B. infans, although Beebe and Crane (1937b, p. 367) consider that these three species are valid. B. exophthalma, having a wide interorbital space, larger eye and swollen head profile is clearly separable from the other three species which have a narrow interorbital region and in general, a smaller eye. Characteristic of both B. infans and B. exophthalma is the high number of dorsal fin-rays (300–350) and anal rays (about 30 less than the dorsal). B. bowersii, on the other hand, has only about 260 dorsal rays and 230 anal rays as well as a long postorbital region, clearly longer than in B. infans or B. exophthalma. The fin-rays have not as yet been counted in the type of B. gilli, and thus the case for the establishment of B. gilli as a species distinct from B. infans, is not so well defined, at least on this character. Bean's description of the type of B. gilli omitted all fin-ray counts and the number of lateral line pores; in addition, the tips of the jaws were broken off, although Bean was apparently unaware of this, with resultant errors in proportional measurements referred to the head. From more detailed examinations of the type by Bean (Parr, 1932, p. 13) and by Beebe and Crane the following information was added: the interorbital width is only one-half the diameter of the eye; there is no bulge in the profiles near the eyes; the eye is contained in the postorbital length about 2.2 times; there are 177 or 178 pores in the lateral line behind the pectoral origin and three in front of it; the anal originates at the vertical between the 18th and 19th pores behind the pectoral base.
In Roule and Bertin's study of 30 examples of Borodinula which they referred to B. infans, they found that the eye was contained in the postorbital 2.5–6.0 times and there were 166–194 pores in the lateral line. The relationship between the diameter of the eye and the interorbital width was not recorded in this account so on this character the type of B. gilli is not readily comparable; but it would page 5
appear that if the illustrations of B. infans by Roule and Bertin (1929, p. 25, figs. 10 and 11) are representative, then the interorbital would be about equal to the diameter of the eye in this species. In the type of B. gilli the interorbital is contained twice in the diameter of the eye.
Chapman's specimen (1940, p. 13), taken from close to the type locality of B. gilli and referred to this species, was more completely described than the type. It is clearly distinct from B. infans. The dorsal rays number 260, the anal 205; there are 156 pores in the lateral line (a value unusually low even for the genus as a whole: in 24 specimens of Borodinula infans in which the lateral line pores were counted by Roule and Bertin, the lowest count was 166 with the number not lower in shorter specimens); the interorbital width is contained twice in the eye, the eye in the postorbital about 3.3 times; there is no tendency for the eye to bulge into the profile of the head. Other proportions are scarcely definitive enough to be used as specific characters.
The above comparisons are presented to show that while the type of B. gilli can only be held distinct from B. infans on the insecure characters of narrow interorbital space, slightly larger eye and geographic discontinuity, Chapman's specimen, referred to B. gilli, is more clearly distinguishable from B. infans, whatever the type of B. gilli may eventually prove to be. Disregarding fin-ray counts in any case, Chapman's specimen is closer to the latter on other characters than to B. infans, and the fact that this specimen was taken close to the type locality of B. gilli cannot be ignored.
In the following account two species of Borodinula are described from four specimens taken in 500–600 fathoms from Cook Strait; three are identified with B. gilli, the fourth, damaged, with B. infans.
Borodinula gilli (Bean, 1890)
Labichthys gilli Bean, 1890. Proc. U.S. Nat. Mus., 13: 455.
Avocettina infans Brauer, 1906 (partim). Wiss. Ergebn. "Valdivia" 15 (1): 129.
Avocettina infans Roule and Bertin, 1929 (partim). Oceanogr. Rep. "Dana" Exped. 1920–22, 4: 22–23.
Avocettina gilli Beebe and Crane, 1937b. Zoologica, N.Y., 22 (4) 27: 367–368.
Avocettina gilli Chapman, 1940. Occ. Pap. B.C. Mus., 2: 12–14.
Material Examined
Two specimens: Collection VUZ 85; 600 fathoms; April 19, 1957; total lengths 517 mm and 542 mm; adults.
One specimen: Collection VUZ 86; 600 fathoms; April 20, 1957; total length c. 610 mm; adult.
Specimens Previously Recorded
One specimen: Station 2859; 1569 fathoms; August 29, 1888: east of Prince of Wales Island, Alaska; lat. 55° 25′ N., long. 136° 20′ W; total length 463 mm; adult; the type specimen—Bean, 1890, p. 455.
One specimen: Station 1248A; up to 164 fathoms; January 1, 1935; coast of Alaska; lat. 51° N., long. 130° 48′ W; total length 420 mm; adult—Chapman, 1940, p. 12.
Description
(Text-fig. 1, A-1)
Body extremely elongate, moderately compressed anterior to vent, strongly compressed and band-like posteriorly; depth of body greatest at a point half-way along caudal region, where it is contained three times in postorbital length, but body tapering gradually to tip of tail. Head long, with an extended snout and much-produced, toothed jaws; fins delicate, scales absent.
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Text-fig. 1.—Borodinula gilli 542 mm t.l. Fig. A—Lateral view. Fig. B—Lateral view of head. Fig. C—Dorsal view of head. Fig. D—Ventral view of head. Fig. E—Lower dentition. Fig. F—Upper dentition. Fig. G—Ventral view of maxillary-ethmovomerine articulation to show tooth pattern. Fig. H—Ventral view of ethmovomerine teeth. Fig. I—Lateral view of ethmovomerine teeth.