Other formats

    Adobe Portable Document Format file (facsimile images)   TEI XML file   ePub eBook file  

Connect

    mail icontwitter iconBlogspot iconrss icon

Deep-Water Crustacea of the Genus Sergestes (Decapoda, Natantia) from Cook Strait, New Zealand

Sergestes (Sergia) potens Burkenroad, 1940

Sergestes (Sergia) potens Burkenroad, 1940

  • 1905. Sergestes bisulcatus (non Wood-Mason) Stebbing, Mar. Invest. S. Africa IV: 87, Pl. XXIV A.
  • 1910. Sergestes bisulcatus (non Wood-Mason) Stebbing, Ann. S. Afri. Mus. VI (IV): 381.
  • ? 1925. Sergestes grandis (non Sund) Hansen in Calman, S. Afri. Fish. Mar. Biol. Surv. 4 (III): 23.
  • 1940. Sergestes (Sergia) potens Burkenroad, Ann. Mag. Nat. Hist. 11, VI: 48.
  • 1950. Sergestes phorcus (non Faxon) Barnard. Ann. S. Afri. Mus. XXXVIII: 641. fig. 120.
page 16

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.)

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):

Male. Female.
Length entire 87.5 113
Length carapace 24 32
Length rostrum 1.5 2
Length abdomen 51 66
Length 3rd somite abdomen 9 11
Length 6th somite abdomen 12 15
Length telson 11 13
Length 3rd maxilliped 32.5 45
Length 1st pereiopod 24.5 34
Length 2nd pereiopod 35 48
Length 3rd pereiopod 38.5 60
Length 4th pereiopod 28.5 37
Length 5th pereiopod 16.5 21

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.

page 19

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.

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.

page 20

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.

page 21

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.