Material Examined

Victoria University, Zoology Department, Cook Strait Collections

Coll. VUZ 24 (Station FOR) 41° 36′ 30″ S., 174° 57′ 30″ E., 14/1/56, 1800–1900 hrs., N2M at about 100 fms. over 540 fms.—1♂9 mm.

VUZ 25 (Station FOS) 41° 37′ S., 175° 2′ E., 14/1/56, 2140–2300 hrs., N2M at about 100 fms. over at least 300 fms.—6 ♂♂ 8–10 mm, 7 ♀♀ 7–15 mm, 1 unsexed 8 mm.

VUZ 26 (Station FUG) 41° 37′ S., 175° 4′ E., 14/1/56, 2315–0100 (15/1/56) hrs., BT at about 100 fms. over 150–300 fms.—1 ♂ 8 mm.

VUZ 27 (Station FUD) 41° 37′ S., 175° 5′ E., 15/1/56, 0125–0225 hrs., N2M at about 50 fms. over at least 100 fms.—1 ♀ 9 mm.

VUZ 28 (Station SAR) 41° 29′ S., 174° 57′ E., 15/1/56, 0415–0545 hrs. BT at about 130 fms. over at least 200 fms.—1 ♂ 7 mm.

VUZ 51 (Station DOP) 41° 35′ S., 174° 53′ E., 22/2/56, 1730–1830 hrs., N2M struck bottom at about 200–300 fms.—2 ♀♀ 8.5–9 mm.

VUZ 52 (Station DOR) 41° 35′ S., 174° 57′ E., 22/2/56, 2020–2130 hrs., N2M at about 100 fms. over at least 400 fms.—11 ♂♂ 8–14 ram, 9 ♂♂ 7–14 mm.

VUZ 53 (Station HUL) 41° 41′ S., 175° 17′ E., 23/2/56, 0100–0215 hrs., BT on bottom at about 250–350 fms.—1 ♂ 10 mm, 6 ♀ 7.5–8.5 mm.

VUZ 54 (Station GUL) 41° 39′ 30″ S., 175° 17′ E., 23/2/56, 0300–0450 hrs., BT on bottom between 50–200 fms.—1 ♀ 11 mm.

VUZ 57 (Station BOOS) 42° 1′ 30″ S., 174° 58′ E., 31/3/56, 0230–0540 hrs., N2M at about 300 fms. over at least 1,200 fms.—4 ♀♀ 8–10 mm.

VUZ 81 (Station KUB) 41° 45′ S., 175° E., 17/2/57, 0920–1100 hrs., BT at about 600 fms. over about 870 fms.—1 ♂ 11.5 mm.

VUZ 82 (Station JUG) 41° 42′ 30″ S., 175° 9′ E., 17/2/57, 1200–1355 hrs., BT at about 500 fms. over 550 fms.—2 ♀♀ 14 mm.

VUZ 83 (Station JUG) as preceding, 1430 hrs., BT struck bottom at about 550 fms.—1 damaged specimen.

VUZ 84 (Station CUK) 41° 47′ S., 175° 02′ E., 19/4/57, 1500–1700 hrs., N2M at about 400 fms. over about 800 fms.—5 ♂♂ 9–14 mm, 8 ♀♀ 9–14.5 mm, 2 damaged 10–15 mm.

VUZ 85 (Station CUK) as preceding, 1915–2400 hrs., N4M at about 600 fms. over about 800 fms.—1 ♂ 12 mm, 1 ♀ 8.5 mm.

VUZ 94 approx. 42° 2′ S., 175° 22′ E., 24–25/8/57, 1845-0115 hrs., N4M at 500–600 fms. over about 1,400 fms.—1 ♀ 14 mm.

VUZ 100 (Station FOJ) 41° 36′ S., 174° 44′ E., 29/8/57, 1315–1430 hrs., BT on bottom at about 380 fms.—1 ♀ 14 mm.

Chatham Islands 1954 Expedition (D.S.I.R.)

Station 7, Chatham Rise, 40° 42′ S., 179° 55′ E., 24/1/54, 1880 hrs., BT on bottom at 280 fms.—1 ♀ 9.5 mm.

Station 52, Chatham Rise, 44° 04′ S., 178° 04′ W., 10/2/54, 0632 hrs., BT on bottom at 260 fms.—1 ♂ 8 mm, 1 ♀ 8.5 mm.

Dominion Museum Collections

23/1/57, off Taiaroa Head, Otago, 45° 38′ S., 171° 12′ E., about 0200 hrs., trawl at about 150 fms. over 600 fms.—1 ♂ 7 mm, 2 ♀♀ 5–7 mm.

B.S. 204 (net 4), White Island Trench, Bay of Plenty, 37° 29′ S., 177° 17′ E., 25/2/57, N2M on 500 fms. wire, over about 600 fms. M.V. Alert—1 damaged, about 8 mm.

Portobello Marine Biological Station Collection, Dunedin

Station Alert 54.13A, N.E. of Otago Heads, Canyon A, 2/3/54, BT on bottom at about 300 fms.—4 ♀ 8.5–13.5 mm, 1 damaged 14 mm.

Station Alert 54.17 (as for 54.13A)—2 ♀ 9–11 mm.

Specific Diagnosis

A relatively small, fragile shrimp with long appendages and characteristically prominent laterally-directed eye stalks.

Rostrum short, acute, projecting slightly beyond the anterior margin of the carapace and with the dorsal margin weakly convex. Supraorbital crest armed with spine; cervical groove distinct, terminating near the prominent hepatic spine. Suprabranchial groove and ridge well marked.

Eyes large, black, cornea wider than stalk, no protuberance (ocular tubercle) on the latter. Antennular peduncular segments long and relatively slender, second and third together subequal to proximal, third a little longer than second. Third maxillipeds not greatly enlarged, subequal in length to 3rd pereiopods. Only one margin of the two distal segments of the 5th pereiopods fringed with setae.

Male with petasma as shown (Figs. 4, 5); processus ventralis long and armed distally with several small clumps of spiniform projections; lobus terminalis only a little shorter, with several terminal "crochets" (retractible hooks); lobus connectens short, triangular and with anterior face armed with closely packed crochets; lobus armatus curved, long and reaching to the lobus page 11

Figs. 1–5. Sergestes arcticus.—Fig. 1, carapace, lateral view (anterior organ of Pesta represented by broken circle) ♀. Fig. 2—Anterior part cephalothorax, lateral view (setae omitted) ♀ 10 mm. Fig. 3—immature left petasma, posterior view, ♂ 8 mm. Fig. 4—Right petasma. posterior view, ♂ carapace length 12 mm. Fig. 5—As preceding, anterior view.
Figs. 6–9. Sergestes japonicus.—Fig. 6—Carapace, lateral view, ♀ Fig. 7—Anterior part cephalothorax, lateral view (setae omitted), ♀ 28 mm. Fig. 8—Left petasma, posterior view, ♂ 21 mm. Fig. 9—As preceding, anterior view.

page 12connectens, with single row of crochets along inner margin; processus uncifer long, hooked and reaching to the base of the lobus armatus, no lobus inermis present.

Female with two curved teeth medially on coxa of 3rd pereiopod.

Carapace length of New Zealand specimens up to 15 mm, males tend to be smaller than females.

Branchial Formula

I have followed Burkenroad (1937b) in regarding the dorsal series of gills in Sergestes as arthrobranchs rather than pleurobranchs. Thus the branchial formula of the New Zealand specimens of S. arcticus is as follows:

l represents a branchial lamella (i.e., a rudimentary arthrobranch).

This formula agrees with the records, but not the terminology, for S. arcticus given by Smith (1882, 1884) and Hansen (1903, 1922) and also with Caiman's (1909: 280) formula for the genus Sergestes.

In the New Zealand specimens the anterior arthrobranch of the 3rd pereiopod is nearly twice the length of the anterior branch of the 4th. The posterior arthrobranch of the 3rd pereiopod, clearly not rudimentary, is larger than the posterior branch, and only a little shorter than the anterior branch, of the 4th pereiopod.

Colour in Life

S. arcticus in life is transparent with red chromatophores scattered over the body and appendages, these being mainly concentrated on the carapace and mouth parts. Within the carapace itself the black stomach and the bright scarlet organs of Pesta are especially prominent.

In addition to the above general description the following details have been observed from fresh specimens. The chromatophores are especially concentrated dorsally on the carapace and the first two abdominal segments, while the rest of the abdomen is almost colourless except for some patches of chromatophores on the ventral surface of the 6th segment and at the base of the tail fan. The cornea is jet black and the eye stalk bears a few scattered red chromatophores. Of the mouth parts the 2nd maxilliped is the most prominent, many chromatophores occur on all segments especially on the distal two. All the setae of the mouth parts are themselves bright red. The ventral surface of the cephalothorax is also red and there is usually one chromatophore on the coxopodite of each pereiopod. In the male the petasma is sprinkled with small chromatophores at the same concentration as on the pleopods. Of the organs of Pesta only the anterior pair, slightly dorsal and posterior to the base of the mandible, are clearly visible through the carapace. These appear as circular scarlet bodies, becoming opaque yellow after preservation. The more dorsal organs cannot be clearly seen through the musculature of the body, but appear as strongly pigmented scarlet areas within the carapace.

Previous more or less complete descriptions of the colour of this species have been given by Kemp (1910a), Hansen (1922: 63, Pl. I, figs. 1, 2) and Holthuis

Length of Antennal Flagellum

The flagellum is so seldom preserved unbroken that its length is not often recorded. A female specimen of S. arcticus with a carapace length of 14 mm had an undamaged flagellum of 170 mm, the characteristic crescentic bend occurred after 54 mm and every segment of the remaining 116 mm was armed with the pair of curved setae so often described in this genus. This example can be compared to Stebbing's (1905) statement that his S. gloriosus (S. prehensilis Bate), with a carapace length of 15 mm, had an antennal flagellum 163 mm in length.

Systematic Position

This New Zealand form shows all the features of the "S. arcticus group" of the subgenus Sergestes s.s.: 3rd maxillipeds subequal with 3rd pereiopods, the two distal segments of the 5th pereiopods setose on only one margin, 3rd segment of antennular peduncle shorter than 1st, processus uncifer terminally hooked. Within this group it can be fully distinguished by rostral and branchial features from the only other species described, the North Pacific S. similis. Though the petasma of S. similis is undescribed, that of our New Zealand form agrees in every detail with the highly characteristic organ of S. arcticus excellently illustrated by Hansen (1922) and others.

Distribution

This extremely well known and abundant Atlantic species has been recorded in all regions of the North Atlantic from the coasts of Norway and Greenland to the Mediterranean and the Canary Islands, while in the South Atlantic it has been taken off the French Congo, South Africa and Uruguay. However, in the Pacific it has been reported from only two localities, off Chile (Holthuis, 1952) and from Challenger Station 159, south of Australia (Hansen, 1903: 59). Though Gurney and Lebour (1940) state that an acanthosoma larva from Terra Nova Station 251 (54° 2′ S. 177° 0′ W, south of New Zealand) "seems to be indistinguishable from S. arcticus", adults of this species have not been recorded from the New Zealand area until now.

Sund (1920) found S. arcticus to be the commonest species of the genus in the North Atlantic and stated that it had virtually the same distribution in that ocean as the genus Pasiphaea. Also Ekman (1953) mentions that S. arcticus in the Atlantic is one of the few bathypelagic species which are truly cosmopolitan with regard to temperature. By this he means that the species is found in equatorial as well as in both north and south cold-water regions, though it might avoid waters in the highest latitudes.

S. arcticus has almost invariably been taken in Cook Strait in association with an abundant bathypelagic Pasiphaea, very similar to, but distinct from, the North Atlantic P. sivado (Risso).

Bathymetric Distribution

S. arcticus has been taken in nearly every bathypelagic haul made in Cook Strait between 50 and 600 fms. However, as all nets used have been of the "open" type, specimens could have been taken at any depth between the surface and that at which the net was being used. Only four collections (V.U.Z. 25, 52, 53, 84) contain sufficient numbers of specimens to warrant individual discussion. The two most interesting were both made shortly before midnight at about 100 fms., a total of 34 specimens being taken for 2½ hours work. A haul made shortly after 1 a.m. at about 300 fms. took 7 specimens, while another made at 400 fms. after 4 p.m. caught 15 specimens.

Thus it can be said that adult S. arcticus in Cook Strait can be found during the night from at least 50 fms. to about 300 fms. with an apparent concentration at about 100 fms., while during the day there may be another concentration at about 400 fms. Sund (1920) found that during the Michael Sars North Atlantic Expedition adults were not common above about 250 fms. though they had been taken up to 100 fathoms and even less. During work with "closing" nets on the Atlantis in the Western North Atlantic, Welsh and Chace (1938) took S. arcticus between 100 and 500 fms. and later were able to show (Waterman et al, 1939) that though the centre of average vertical distribution was a little above 300 fms. extensive diurnal vertical migration of at least 100 and as much as 200 fms. takes place, some specimens being in less than 100 fms. between about 8 p.m. and 4 a.m.

Size at Maturity and Partial Parasitic Castration

Male specimens with a carapace length of less than 9 mm invariably have a petasma with the various lobes and crochets incompletely developed. The immature petasma illustrated (Fig. 4) is from a specimen with a carapace length of 8 mm and represents an even earlier stage than that figured by Holthuis (1952). Those specimens with carapace lengths of 10 mm and more always have, with certain exceptions mentioned below, mature petasma. Thus males, and we must assume, females, usually mature at a carapace length between 9 and 11 mm.

Many specimens have small or large larval nematode worms loosely coiled in the posterodorsal portion of the cephalothorax immediately beneath the carapace. Collection VUZ 25 had one so parasitised out of 14, collection VUZ 52 had 6 parasitised out of 20 and collection VUZ 84 had 5 out of 15, making a total of 12 of these 49 specimens parasitised (approx. 24%). Specimens with such a nematode in the area of the gonads have the dorsal mid-line of the carapace characteristically weakly convex, and males, at least, show partial parasitic castration. Thus no parasitised male seen had a mature petasma, even specimens with carapace lengths of 14 mm had this organ small and still relatively undeveloped.

Material Examined

Victoria University, Zoology Department, Cook Strait Collections.

Collection VUZ 84 (Station CUK) as given above—1 ♀ 20 mm.

Extended Diagnosis

The single female specimen available has the cephalothorax separated from the abdomen and both 3rd maxillipeds and certain pereiopods missing. A short description of the main characters of this damaged specimen is given below.

A relatively large, attenuated, firm-bodied shrimp with long appendages and prominently ridged carapace.

Rostrum relatively small, compressed, very slightly raised above the anterodorsal mid-line of the carapace and hardly projecting beyond the anterolateral margin of the carapace. Anterior margin of the rostrum with an acute tip flanked dorsally and ventrally with short concave portions. Carapace relatively long and attenuated, greatest depth, at posterior margin, a little less than two-fifths the length. Supraorbital crest prominent, but supraorbital spine absent. Hepatic spine small but distinct. Cervical groove well defined dorsally and laterally, almost continuous anteriorly with a well defined lateral ridge running from anterior to the hepatic spine towards the base of the antenna. Suprabranchial groove and ridge prominent with a slightly less prominent horizontal ridge laterally across the branchial region.

Telson weakly grooved dorsally, distally setose with no dorsal spinules present.

Eyes not large, cornea considerably shorter but broader than distal segment of ocular peduncle. Ocular tubercle present, broader than high.

Antennular peduncle relatively narrow and attenuated, proximal segment a little longer than the third, which is itself longer than the second. Antennal scaphocerite, with outer margin distinctly convex, reaches a little beyond the proximal third of the third segment.

Mouth parts as for genus. As both 3rd maxillipeds are missing, it is impossible on this feature to be sure of the group to which this specimen belongs.

The 1st pereiopod reaches a little beyond the distal end of the antennular peduncle and is non-chelate. 2nd and 3rd pereiopods extend well beyond the antennular peduncle, and both bear minute chelae of the type apparently characteristic of the "S. corniculum" and the "S. sargassi" groups (see Burkenroad, 1937a: 320). Here the fixed finger is shorter than the free finger, both bearing distally a fan of setae, while the fixed finger and a portion of the hand bear a conspicuous longitudinal series of very long plumed setae exactly as shown by Hansen (1922, Pl. VII, figs. g–h). The ischia of 1st and 2nd pereiopods bear a spine disto-laterally. The 4th and 5th pereiopods are both of the compressed laminar type usual in the genus, the 4th reaching to the distal end of the antennal peduncle, while the 5th, with both margins of the two distal segments setose, reaches a little beyond the distal half of the merus of the 4th.

Setose portion of external margin of uropodal exopodite half as long again as non-setose portion. No tooth present on this outer margin.

Female with no teeth or lobes medially on coxa of 3rd pereiopod, but with a small spinule posterodistal to the opening of oviduct.

Branchial Formula

As given for S. arcticus above. The anterior arthrobranch of the 3rd pereiopod is nearly twice the length of the anterior branch of the 4th, which is a little longer than the posterior branch of the 4th, the latter being subequal to the posterior branch of the 3rd pereiopod.

Colour in Life

Organs of Pesta present. The coloration of this "half red" species was observed in the fresh state as follows. Red stellate chromatophores were scattered all over body and appendages, but with a greater concentration on the carapace. The posterior half of the dorsal surface of the carapace had a distinct purplish-blue cuticular pigment present, and another small patch of the same pigment occurred laterally on the carapace in the area of the anterior organ of Pesta. The stomach is clearly visible through the carapace as a large greenish-black anterodorsal mass.

Systematic Position

As the two distal segments of the 5th pereiopods are setose on both margins and organs of Pesta are present, the specimen belongs to either the "S. corniculum" or the "S. sargassi" groups of the subgenus Sergestes s.s. The absence of both 3rd maxillipeds in the only specimen available, does not allow it to be placed in one of these two groups, as the relative length of this appendage is apparently the only feature distinguishing one group from the other (see Burkenroad, 1937a: 320). However, owing to the great similarity in appearance between this specimen and the illustrations of S. corniculum, especially as regards the ridges, grooves and shape of the carapace, I believe it to be closely related to that species. Assuming it to belong to the "S. corniculum" group, the absence of a supraorbital spine distinguishes it from S. corniculum, S. disjunctus and apparently from the inadequately described S. nipponensis; the presence of a transverse groove between the hepatic spine and the lateral ridge anterior to it distinguishes it from S. rubroguttatus and S. coalitus; while the low ocular tubercle distinguishes it from S. erectus. This leaves only S. seminudus to be considered. This species described from Indonesian waters by Hansen (1919), is very similar indeed to the New Zealand specimen, differing only to a small extent in the relative lengths of the segments of the antennular peduncle. However, our female specimen cannot be definitely identified with S. seminudus (if. indeed, it belongs to the "S. corniculum" group) until mature males arc taken and the petasma compared to that of Hansen's species.

It should be noted here that Burkenroad (quoted by Gurney and Lebour, 1940: 38) states that there are three species in the Atlantic confused with S. corniculum "but he is not at present able to give a final opinion or names for the species which he has distinguished". In the same year Burkenroad (1940) described five new species belonging to the S. corniculum and the S. sargassi groups, by comparing them, without illustrations, to one another and to S. seminudus, S. henseni and S. "sargassi Ortmann" of Hansen. This does not allow us to know what he means by these species. Until his promised revision of the genus (1937a, 1940, 1945) is published, it is very difficult, if not impossible, to identify many species which he has dealt with in a preliminary manner.

Material Examined

Victoria University, Zoology Department, Cook Strait Collections

—/4/41. East side of Palliser Bay, 30 fms. from stomachs of groper, Polyprion sp. and ling, Genypterus blacodes (Bloch & Schn.) Coll. Pawley brothers—25 ♂♂ 18–29 mm, 22 ♀♀ 14–32 mm.

Coll. VUZ 83 (Station JUG) as given above—1 ♂ 27 mm.

VUZ 100 (Station FOJ) as given above—1 ♀ 20 mm.

Dominion Museum Collections

6/6/42. Cook Strait, Middle Ground, 60 fms. gut contents of single groper P. oxygeneios (Bloch & Schn.), Coll. C. Kaberry, Marine Dept. Wellington—23 ♂♂ 21–28 mm, 8 ♀♀ 21–25 mm.

Description

This description is mainly based on a male specimen, with carapace length 23 mm, collected by the Pawley brothers in 1941.

A large, deep-bodied, heavily-built shrimp with relatively soft integument and prominent eyes.

Rostrum relatively large, compressed, directed obliquely dorsally; anterior margin produced in its centre into a short acute point and with a small acute tooth, sometimes rudimentary, on anterodorsal margin. Carapace deep, greatest depth, across branchial region, just under half greatest length. Supraorbital and hepatic spines absent. Cervical groove weakly defined laterally, not continuous dorsally; posterior cervical groove apparently absent; supra branchial groove and ridge weak.

The 6th abdominal segment, which is longer than the telson, ends posteriorly with a minute dorsal spinule. The telson is acute distally and dorsally grooved with three pairs of minute spinules on the distal portion of the dorsal surface.

Eye with cornea large, considerably wider and also longer than distal segment of ocular peduncle. No ocular tubercle present.

Antennular peduncle relatively short and stout, proximal segment not as long as second and third together, third a little shorter than second and twice its own depth. Antennal scaphocerite reaches almost to centre of this third peduncular segment.

Mouthparts as for genus. The 3rd maxilliped is relatively long and slender, but shorter than the 2nd or 3rd pereiopods; it extends a little beyond the distal end of the antennular peduncle. The dactylus is divided into six and the propodus into two subsegments.

The 1st pereiopod reaches to about the middle of the propodus of the 3rd maxilliped and is non-chelate. The 2nd and 3rd pereiopods both reach well beyond the antennular peduncle and are both minutely chelate. The 4th and 5th pereiopods are both of the compressed laminar type usual in the genus.

Non-setose portion of external margin of uropodal exopodite twice length of setose portion. Endopodite a little more than two-thirds length of exopodite.

Male with petasma as shown (Figs. 15, 16); processus ventral is wide at base with slender, unarmed tip, relatively short, not reaching as far as lobus armatus or terminalis. Lobus armatus long, subequal or longer than lobus terminalis, armed with 3 to 5 crochets distally and a number along the inner margin; well-defined lobus accessorius at base, armed with several crochets. Lobus terminalis and lobus connectens both armed distally and both produced proximally into an armed protrusion. The unarmed lobus inermis projects beyond the lobus terminalis and is subequal with the lobus connectens.

Female with posterior margin of 5th thoracic sternite convex and bulbous and coxa of 3rd pereiopod produced medially into two blunt lobes.

Branchial Formula

As given for S. arcticus above. The posterior arthrobranch of the 3rd pereiopod is about four-fifths the length of the anterior one, subequal to the anterior arthrobranch of the 4th pereiopod and a little longer than the posterior branch of this limb.

Size

A size frequency graph of the 25 males and 22 females in the Pawley brothers 1941 collection is given in Fig. 19. In it males and females have been treated together, as they both reflect the same trends. This graph shows that the majority of the specimens, 73%, are in the restricted size range of 23 to 26 mm (carapace length). If we can assume that the sample reflects the size composition of the shoals on which page 17

Fig. 10. Sergestes cf. S. seminudus, carapace, lateral view (anterior organ of Pesta represented by broken circle) ♀.
Figs. 11–18. Sergestes potens. Fig. 11—Carapace, lateral view, ♂. Fig. 12—Left scaphocerite, ventral view (setae omitted), ♀ 27 mm. Fig. 13—Left uropod, ventral view (setae omitted), ♀ 27 mm. (Figs. 11–13 drawn to same scale. Photophores represented in black.)
Fig. 15—Right petasma, posterior view, ♂ 24 mm. Fig. 16—as preceding, anterior view.
Fig. 17—Anterior part cephalothorax, lateral view (setae omitted), ♂ 23 mm. Fig. 18—Diagrammatic view ventral surface to show photophore distribution. (Bases of appendages open circles, photophores in black.)

page 18 the fish were feeding, the uniformity of size range within these shoals should be noted.

The following measurements were taken from mature specimens of both sexes (mm):

The male was chosen from the commonest size range (carapace length 24 mm) while the female is the largest specimen in the collection (length entire about 113 mm). This female is, as far as I can ascertain, only surpassed in size by one other specimen of the genus Sergestes recorded in the literature. This is the type male of the closely related S. (Sergia) maximus Burkenroad, 1940, with a length of about 136 mm (carapace length 41.5 mm). The type female of S. (Sergia) inous Faxon, 1893, is also given as 113 mm in length. The length entire is measured from the tip of the rostrum to the posterior tip of the telson and is inaccurate, due to the difficulty in extending the abdomen.

Colour in Life

The only specimens seen in a fresh condition were the damaged female from Collection 83 and the undamaged female from Collection 100. Each was examined within a few hours of capture and the following colour notes combine the observations made on both:

Entire body and appendages uniform scarlet, eyes black, organs of Pesta absent, numerous intense purple lens-less photophores (fading to yellow in preservative) arranged as follows:

Carapace: An irregular patch present behind base of antennule and above ventrolateral angle, an irregular row in roof of branchial chamber at level of suprabranchial ridge.

Eyestalk: None.

Antennular Peduncle: 2 distoventrally on 3rd segment.

Antennal Peduncle: 1 distolaterally on penultimate segment, 1 distoventrally on ultimate segment.

Scaphocerite: 1 ventrally at articulation and a longitudinal row of about 9–11 irregularly spaced in distal two-thirds. One long streak and 1 small spot diagonally in proximal third.

Mandible: 1 at distal end of proximal segment of palp.

1st Maxilla: None.

2nd Maxilla: 5 on anterior half of exopodite and a large kidney-shaped one on posterior half.

1st Maxilliped: 1 on the penultimate segment of the exopodite.

2nd Maxilliped: 1 proximally on merus, 1 distally on both carpus and propodus.

3rd Maxilliped: 1 distodorsally on both merus and carpus, and 1 distoventrally on propodus.

1st Pereiopod: 1 proximally on ischium, and 2, one larger than the other, proximally on the merus.

2nd Pereiopod: 1 proximally and 1 distally on ischium, none on merus.

3rd Pereiopod: 2 on ischium as in 2nd pereiopod, row of 8–13 on merus.

4th Pereiopod: 2 on ischium as in 2nd pereiopod, 1 distally on merus, and 2 distally on carpus. 2 internal pigmented patches were visible by reflected light, 1 on ischium and 1 proximally on merus; these were found on dissection to be similar in structure to the externally visible photophores.

5th Pereiopod: 2 on ischium as in 2nd pereiopod, 1 distally on both merus and carpus.

1st Pleopod: 1 proximally on exopodite.

2nd–5th Pleopods: 2 distolaterally on coxopodite, 1 distally on basipodite, and 1 proximally on exopodite.

Uropod: 1 at proximomedial angle of both endopodite and exopodite, an irregular streak and spot longitudinally on proximal third and an irregularly spaced longitudinal row of about 5 on distal third of exopodite.

Thoracic Sternum: 1 between bases of antennae. 1 large one each side of labrum. 2 between bases of lst-2nd maxillipeds. 1 between bases of 2nd-3rd maxillipeds. 1 between bases of 3rd maxillipeds. 1 between bases of lst-2nd pereiopods. 1 between bases of 2nd-3rd pereiopods. 1 median and 1 pair between bases of 3rd-4th pereiopods. 1 between bases of 4th pereiopods. 1 median and 2 pairs (1 large and 1 small) between bases of 4th and 5th pereiopods. 1 median pair between bases of 5th pereiopods. 1 large one behind base of each 5th pereiopod.

Abdominal Sternum: Each sternite (1st–6th) with one prominent antero-lateral pair and in addition in the midline: 1st sternite, 1 pair behind bases of pleopods. 2nd sternite, 1 pair and 1 unpaired in front of, and 1 pair behind, bases of pleopods. 3rd sternite, 1 pair and 1 unpaired in front of, 1 unpaired between and 1 pair behind, bases of pleopods. 4th sternite, 1 pair in front of, 1 unpaired between, and 1 unpaired behind, bases of pleopods. 5th sternite, 1 unpaired between and 1 unpaired behind, bases of pleopods. 6th sternite, a median longitudinal row of 4–6 irregularly shaped photophores (the posterior one wider than long).

Fig. 19. Sergestes potens. Size frequency histogram for the 47 specimens collected by the Pawley brothers in 1941.

Abbreviations Used In Figures.

la— lobus armatus. lac— lobus accessorius. lc— lobus connectens. li— lobus inermis. It— lobus terminal is. Pu— processus uncifer. PV— processus ventralis.

Systematic Position

The presence of lens-less dermal photophores on the body and appendages indicates that this species belongs to the "S. robustus" group of the subgenus Sergia. Within this group the characters of the petasma, and photophore distribution where known in any detail, immediately distinguishes it from all species except S. bisulcatus, S. phorcus, S. grandis and S. potens. Thus it remains to examine the relationships of these species and to compare them with the New Zealand specimens described above.

In 1893, Faxon gave a very short and incomplete "preliminary description" of a new species of Sergestes, S. phorcus, taken by the U.S. Fish Commission Steamer Albatross, during 1891, from a number of stations between the Galapagos Islands and the Gulf of California. When he published his definitive account of the Stalk-Eyed Crustacea of this Expedition in 1895, he more fully described and illustrated this species, but placed it doubtfully as a synonym of the Indian Ocean S. bisulcatus Wood-Mason, 1891, the latter's description being not detailed enough to permit him to be sure of this identification.

Hansen (1896), in his comprehensive summary of the genus Sergestes, accepted S. phorcus as a synonym of S. bisulcatus in his checklist of species. In 1905, Stebbing described and illustrated two females from South African waters, collected from a depth of 250 to 300 fathoms off a bottom of green sand and mud, and identified them with Faxon's species, though he too was not certain of its association with S. bisulcatus Wood-Mason. Stebbing's specimens were described as "red, fading to orange".

Hansen (1919) in his review of part of the genus, based on a study of the specimens collected by the Siboga Expedition to the Netherlands East Indies, 1899–1900, re-established S. phorcus as a species distinct from S. bisulcatus Wood-Mason on the shape of the rostrum and petasma. Since Faxon's (1895) paper, a further description of S. bisulcatus Wood-Mason had been published by Alcock (1901) and this, with the new illustrations given of the same species by Hansen, made it quite clear that it was distinct from the species illustrated by Faxon (1895) and from that illustrated by Stebbing (1905). In his paper Hansen introduced the special study of the petasma, the male copulatory organs on the first pair of pleopods. He found them of primary systematic importance in the family Sergestidae. On PL I he illustrated in detail the left petasma of S. bisulcatus W.-Mason. He stated (p. 5) that he has seen several adult specimens of S. phorcus in the material collected in the North Atlantic by the Prince of Monaco.

In 1922 Hansen, describing the Sergestes collected during the expeditions of the Prince of Monaco, 1885-1915, admitted that the specimens he identified in 1919 as S. phorcus belonged to a species since described from the North Atlantic as S. grandis Sund, 1920. He further described this species and gave detailed illustrations of the petasma, comparing it with drawings of the petasma of S. phorcus supplied to him by Dr. Waldo L. Schmitt, of the U.S. National Museum from one of Faxon's cotypes. He regarded S. bisulcatus Stebbing (non Wood-Mason) as S. grandis, though only females had been recorded. From the material collected by the S.S. Pickle in South African waters during 1920–21, Hansen (in Caiman, 1925) also identified three females and four immature specimens, collected from 270 fathoms and deeper, as S. grandis Sund.

Burkenroad (1937a), describing Sergestidae from the Templeton Crocker Expedition to the Lower Californian Region, illustrated for the first time the petasma of S. phorcus Faxon. This figure shows clearly the long, gently tapering, lobus ventralis, reaching beyond all the other lobes of the distal portion of the pars media; the lobus terminalis with a weakly developed basal protuberance, though clearly not bilobed; and the lack of a lobus accessorius at the base of the long lobus armatus. Burkenroad also gave a partial record of the distribution of lens-less photophores in this species.

In 1940 Burkenroad gave preliminary descriptions of 18 new species of Sergestes from the collections of the Danish Oceanographical Expeditions in the Dana. S. (Sergia) potens is described from off the coast of South Africa (Station 3975 VII, open N2M on about 300 fms. of wire over about 1,375 fms. off Cape Town), and is stated to be "nearly related to S. phorcus Faxon This species is described as having a petasma much as in S. phorcus and S. grandis, however, the processus ventralis is "expanded at base with slender tip; relatively short, not reaching as far as does the lobus terminalis"; both the lobus connectens and the lobus terminalis are prominently bilobed, each sublobe being armed; and the lobus armatus has "a well-defined lobus accessorius at base larger than that in S. grandis". The specimens from Cook Strait described above agree in every detail with the description of S. potens given by Burkenroad. A partial account of the distribution of the lens-less photophores on the type specimen of this species also agrees in all major features with the list given above; however, Burkenroad records photophores on the merus of the 2nd pereiopod where none are present in our specimens from Collections 83 and 100. As he does not mention the photophores on the merus of the 1st pereiopod, "2nd" may be mistake for "st". Until further fresh material from South African waters is examined, it is impossible to tell if this difference is real or not.

In his "Descriptive Catalogue of South African Decapod Crustacea" Barnard (1950) illustrated and described the petasma and rostrum of two males in the South African Museum from the same haul as Stebbing's (1905) females, but not seen by the latter. From the long lobus armatus and other features he believes these, and consequently Stebbing's specimens, to be S. phorcus Faxon. However, he does not appear to have seen Burkenroad's illustration of the petasma of S. phorcus (1937a) or his description of S. potens (1940). Barnard's specimens, showing the basally expanded, relatively short processus ventralis not reaching as far as the bilobed lobi connectens and terminalis^*, are clearly conspecific with the New Zealand material and also agree, in all points recorded and illustrated, with S. potens already described from South African waters.

Thus is can be seen that the South African records of S. bisulcatus (Stebbing, 1905), S. potens (Burkenroad, 1940), S. phorcus (Barnard, 1950) and probably S. grandis (Hansen, in Caiman, 1925) all refer to the same species, and that species must be known as S. (Sergia) potens Burkenroad, which can now be recorded also from Cook Strait, New Zealand.

Bathymetric Range

The single specimen from Collection 83 was taken during the day in a beam trawl which struck mud bottom at a depth of about 550 fathoms. This had been intended as a bathypelagic haul, and it only unintentionally collected on the bottom. Associated with this specimen of Sergestes potens were one specimen each of the typically bathypelagic natants Sergestes arcticus, Pasiphaea sp. and Acanthephyra cf. quadrispinosa, as well as a specimen of the characteristically benthic genus Sclerocrangon. Similarly the single specimen from Collection 100 was taken during the day in a beam trawl working on the bottom in about 380 fathoms. Although this was primarily a bottom haul, both Sergestes arcticus and Pasiphaea sp. were associated as above. As the three bathypelagic forms, but not S. potens, have been taken on numerous occasions by mid-water nets in Cook Strait, it is reasonable to suppose that the latter, like the crangonid, is a benthic species, at least during the day.

However, all Sergestidae, with the single exception of the shallow-water genus Sicyonella, have been regarded, from the evidence of their statoliths, as nektonic (Burkenroad, 1937b). In particular all members of the genus Sergestes examined, page 22have "autogenous statoliths" (i.e., self-secreted cuticular pellets) rather than exogenous concretions (containing material introduced from outside), such as are found in Sicyonella and other benthic penaeids. I have examined the statoliths of specimens of S. potens from both 1941 and the 1942 collections, as well as one from the Collection 83 specimen, and in every case they consist of transparent oval cuticular pellets, slightly pointed at one end, with no trace of extraneous matter included. I do not consider that the possession of autogenous statoliths is necessarily indisputable evidence against S. potens being at least a partially benthic species as apparently is the case in the Japanese S. (Sergia) lucens as recorded by Nakazawa (1915). This paper is in Japanese, but I have seen, in the British Museum (Natural History), an English abstract, provided by the author himself, and referred to by Gordon (1935: 313). Nakazawa states that S. lucens (recorded as S. prehensilis) lives on a bottom of mud and fine sand during the day in depths down to about 100 fathoms and rises at night to mid-water in winter or to near the surface in summer for "swarming", where, on dark nights in May and June, their luminescence makes a wonderful sight. They are fished in great quantities, about two miles off shore in Suruga Bay, with floatless purse seins lowered to between 50 and 100 fathoms on dark nights, or in conditions of high turbidity after flooding, during the daytime. S. lucens is of great economic importance in Japan, and although the fishery started accidentally in 1894, the total annual catch in 1915 was about 10 million lbs.

Now if S. potens had the same habits as S. lucens and rose to mid-water nocturn-ally, shoals could be swept by tidal currents over shallower water and on sinking with the approach of daylight would be taken in large numbers by groper and ling. These fish are voracious bottom-feeders, being recorded down to at least 150 fathoms. That this commonly and regularly happens in Cook Strait is borne out by the fact that the stomach contents of these two fish seasonally contain bathypelagic fish, squid and shrimp, which normally are taken well below the depth at which the fish were caught. It should be pointed out that the Pawley brothers lifted their lines in the morning and from the fresh appearance of these luminous shrimps they were probably taken only a short time before the fish themselves were actually caught.

Geographical Distribution

Off South Africa; mid-water or on bottom, 250–1,500 fms. (Stebbing, 1905; Caiman, 1925; Barnard, 1950), mid-water (about 100 fms.) over 1,375 fms. (Burkenroad, 1940).

Cook Strait, New Zealand; on bottom 380–530 fms., in fish stomachs 30–60 fms.

Material Examined

Victoria University, Zoology Department, Cook Strait Collections

Specific Diagnosis

A large, fragile shrimp with small eyes and a soft and membraneous integument.

Rostrum relatively small and obtuse, hardly projecting beyond the anterolateral margin of the carapace and little raised above the dorsal surface of the latter. Supraorbital and hepatic spines absent. Cervical groove distinct and continuous over dorsum, weak anterolateral ridge from hepatic region towards base of antenna, suprabranchial ridge present.

Eyes relatively small, cornea barely wider than and about one-third as long as distal segment of ocular peduncle. No ocular tubercle. Segments of antennular peduncle not greatly attenuated, proximal longer than second, which is subequal to third. No distolateral spine on margin of scaphocerite. Third maxillipeds not greatly enlarged, subequal in length to 2nd or 3rd pereiopods.

Male with petasma as shown (Figs. 8, 9); lobus connectens very long, armed on lateral margin and distally on inner margin with crochets; processus ventralis shorter, with distinct distal nick; lobus armatus curved, shorter than processus ventralis, but reaching a little beyond lobus inermis, armed on inner margin with small crochets; lobus terminalis a simple armed projection, smaller than the unarmed lobus inermis, between the latter and the base of the lobus connectens.

Female with single blunt posteromedial projection on coxa of 3rd pereiopod.

Branchial Formula

The relative branchial size and arrangement of the New Zealand specimens agrees with the records for this species (as S. mollis) given by Smith (1884; 1886, Pl. XX, Fig. 5) and Hansen (1922) This differs from the more usual arrangement in the genus, as given for S. arcticus above, in having an arthrobranch and a branchial lamella above the 3rd pereiopod instead of two arthrobranchs.

Size at Maturity

Of the two largest male specimens, each with a carapace length of 21 mm, one is still slightly immature with the petasma as illustrated here, while the other shows the full development of crochets similar to that illustrated by Hansen (1922, Pl. IV, fig. 3 i-m).

Colour in Life

These specimens were uniform scarlet in life with some of the inner mouth parts tinged with purple. This pigment was mainly carried in the cuticle of the body and appendages, although small chromatophores were also present. No dermal photophores of any type present. Organs of Pesta absent.

Systematic Position

The membraneous integument and the lack of dermal photophores place these specimens in the "S. japonicus" group of the subgenus Sergia. The absence of an ocular tubercle and the fact that the cornea is barely wider than the ocular peduncle distinguishes it from S. tenuiremis, S. kröyeri and S. laminatus; the distinctive rostral profile distinguishes it from S. profundus and the branchial formula from S. inous.

The Cook Strait specimens agree in every way with the numerous descriptions and figures of the North Atlantic S. mollis Smith, which has been shown to be synonymous page 24with S. japonicus Bate taken by the Challenger Expedition off Japan (see Hansen, 1896, 1903; Burkenroad, 1940).

Geographic and Bathymetric Distribution

Sergestes japonicus is a well known deep-water species in the North Atlantic. Specimens were taken by the Michael Sars Expedition between about 125 and 1,050 fms. but those with a carapace length of 18 mm and over were never taken above 500 fms. (Sund, 1920). In 1938, Welsh and Chace were able to show from their "closing net" data that it is the only species of Sergestes in the North Atlantic which normally occurs below the level to which light penetrates (i.e., below the photic zone), being found usually below 500 fms. and regularly down to at least 1,000 fms.

Outside the North Atlantic, it has been recorded from only two localities in the Indopacific. The Challenger Expedition took it from deep water off Japan and the Philippines, these records being checked by Hansen (1903).

Thus it is now possible to record this small-eyed, deep-water species from Cook Strait, New Zealand, apparently the first record from the entire Southern Hemisphere.