Pseudorchomene coatsi ( Chilton, 1912 )

D’Acoz, Cedric D’Udekem & Havermans, Charlotte, 2012, Two new Pseudorchomene species from the Southern Ocean, with phylogenetic remarks on the genus and related species (Crustacea: Amphipoda: Lysianassoidea: Lysianassidae: Tryphosinae), Zootaxa 3310, pp. 1-50 : 7-18

Pseudorchomene coatsi ( Chilton, 1912)

( Figs 2–9 )

Orchomenopsis coatsi Chilton, 1912: 477 , pl. 1 figs. 8–9.

Pseudorchomene coatsi . — Schellenberg, 1926: 295. — Lowry & Stoddart, 1983: 381 –385, figs. 72–74 (possibly excluding the specimens from Macquarie Island). — De Broyer et al., 2007: 150, in part (ubi syn.).

Not Pseudorchomene coatsi . — De Broyer, 1983: 193 –195, figs. 72–74 (= P. debroyeri sp. n.).

Type material. Not seen. A male, 17.9 mm, was selected by Lowry and Stoddart (1983) as LECTOTYPE from the syntype series, Royal Scottish Museum 1921.143.938, station 411, off Coats Land, Weddell Sea, 71°01 'S 22°00'W, from baited trap, 290 m, " Scotia ", 12 March 1904.

Material examined. Expedition ARC 94, sta. NA62, King George Island, Admiralty Bay, 62°08'S 58°27'W, 470 m, 29.xii.1963 – 02.i.1964: about 25 specimens, RBINS, INV. 100969 (2 tubes). — R/V “Polarstern” cruise ANT–XIX/3–4 (ANDEEP I & II), West of Elephant Island, sta. 0 83, 61°07.18'S 56°08.84'W – 61°07.09'S 56°08.41'W, 340–350 m, baited trap, 07.ii.2002: 15 specimens, Specimen Ids with corresponding GenBank accession numbers: PC–2609071 ( HM054048 ) [ZMH-43135] (specimen used for illustrations), PC–05100712 ( HM054047 ) [ZMH-43136], PC–SS349 ( GU109245 ) [ZMH-43137], PC–1809076 ( HM054046 ) [ZMH-43138].

— R/V “Polarstern” cruise ANT–XIX/3–4 (ANDEEP I & II), North of Livingstone Island, sta. 114, 61°45'43''S 60°45'28''W – 61°45'31''S 60°45'08''W, 2743–2754 m, baited trap, 17.ii.2002: 2 specimens, Specimen Ids with corresponding GenBank accession numbers: PC–SS2889–4 ( GU109232 ) [ZMH-43139], PC–SS2889–5 ( GU109234 ) [ZMH-43140]. — R/V “Polarstern” cruise ANT–XV/3 ( EASIZ II), Atka Bay, sta. 280/284, Trap 13, 70°27.4'S 07°55.9'W, 550 m, baited trap, 29.ii.1998: 4 specimens, Specimen Ids with corresponding GenBank accession numbers: PC–2210079 ( HM054049 ), PC22100710 ( HM054050 ), RBINS, INV. 100965 (3 tubes). — R/V “Polarstern” cruise ANT–XIX/5 (LAMPOS), South of King George Island, sta. 261, 62°16.44' S 58°15.45' W, 723 m, baited trap, 27.iv.2002: 16 specimens, Specimen Id with corresponding GenBank accession number: PC– 1909075 ( HM054053 ), PC–21090732 (HQ546593), RBINS, INV. 100961. (2 tubes). — R/V “Polarstern” cruise ANT–XXI/2 (BENDEX), Eastern Weddell Sea, sta. 103–104, 70°49'03''S 10°39'47''W – 70°49'10''S 10°39'47''W, 387 m, Fish Trap, 14.xii.2003: 1 specimen, Specimen Id with corresponding GenBank accession number: PC– 0 8100715 ( HM054052 ), RBINS, INV. 100963. — R/V “Polarstern” cruise ANT–XXI/2 (BENDEX), Eastern Weddell Sea, sta. 240, 70°48'58''S 10°39'55''W – 70°49'03''S 10°40'15''W, 406 m, Lander, 22.xii.2003: 5 specimens, Specimen Id with corresponding GenBank accession number: PC–2609076 ( HM054051 ), RBINS, INV. 100964. — R/V “Polarstern” cruise ANT XXI–2 (BENDEX), Eastern Weddell Sea, sta. 288–1, 72°47.58’S 19°29.86’W, 847 m, Fish Trap, 31.xii.2003 – 03.i.2004: 1 specimen, stored in 96% ethanol, RBINS, INV. 100987. — R/V “Ivan Papanin” cruise BELARE, 70°S 23°E, 230 m, Crown Bay, Baited Trap, 23.xii.2008: 10 specimens, Specimen Id with corresponding GenBank accession number: PC–231109112 ( JQ423240 ), RBINS, INV. 100962.

Type locality. Antarctica, off Coats Land, Weddell Sea, 71°01'S 22°00'W, 290 m depth ( Lowry & Stoddart 1983).

Diagnosis. Somites of pereon and pleosome without posterior humps. Mandibular palp inserted well proximal to molar process. Molar process broad. Gnathopod 1: anterior margin of basis convex, palm oblique, basis 3.0 x as long as wide, ischium 6 x, merus 3 x as long as wide, carpus 5 x, propodus 5.5 x as long as wide. Gnathopod 2: carpus 2.3 x as long as wide. Pereopod 3: propodus with about 9–10 spines or pairs of spines (which are well developed). Pereopod 3–7: on propodus, broadest spine of each pair or triplet with tip blunt to very blunt. Coxa 4: rounded posteroventrally. Pereopod 5: coxa slightly longer than broad; basis strongly expanded; merus with setae posteriorly and one fairly slender posterodistal spine. Ratio length/width of merus of pereopod 5–7: 1.3; 1.9; 1.9. Ratio length/width of carpus of pereopods 5–7: 2.0; 2.6; 2.7. Posterodistal angle of carpus of pereopods 5–7 with spines of normal length and stoutness. Pereopod 7: anterior margin of carpus normally spinose, posterior margin of carpus and propodus with posterodistal spines only. Epimeron 3: regularly rounded posteriorly or rounded with trace of angularity. Uropod 3: medial margin of both rami with many long setae, inner ramus reaching or not reaching tip of article 1 of outer ramus.

Description. Based on a female, 19 mm, ANT–XIX/3–4 (ANDEEP I & II), sta. 0 83, West of Elephant Island, 61°07.18'S 56°08.84'W – 61°07.09'S 56°08.41'W, 340– 350 m.

Body without dorsal carina; somites of pereon and pleosome without small posterior bumps. Head with lateral cephalic lobes broadly rounded.

Eyes occupying the most of anterior part of head, much longer than broad, lower part much broader than upper part, anteriorly distinctly concave, posteriorly nearly straight, dark, with fully developed ommatidia.

Antenna 1 distinctly shorter than antenna 2; major flagellum, first article very elongate; accessory flagellum, first article very elongated; calceoli present in males, absent in females.

Antenna 2 about 0.15 x as long as body; peduncular articles 3 to 5 not enlarged, with brush of setae; flagellum 31-articulate, calceoli present in males, absent in females.

Mouthparts forming a quadrate bundle. Epistome carinate, scarcely produced, terminating in small blunt tooth; upper lip broadly rounded, slightly overreaching epistome.

Mandible: incisor process, cutting edge smooth except for small blunt denticle on each side, lateral and medial borders parallel; lacinia mobilis present on left side only, narrowly cylindrical (finger-like), slightly curved, distally slightly dilated with 5 medium-sized dentiform processes; 3 small raker spines and a dense patch of short setules present between incisor and molar processes; molar process broad, elliptic to subovate, transversally ridged and triturative; lateral setigerous crest arising from proximal 0.3 of molar process; palp 3-articulate, attached midway, well proximal to molar process; article 1 without setae, article 2 longest with row of 21–22 strong distal and subdistal A2-setae, article 3 of palp 0.60 x as long as article 2, 3.5 x as long as wide, with 1 proximal A3-seta, a row of 21–23 D3-setae on distal 0.7 (these setae are slightly shorter than width of article 3), and 3 E3-setae.

Maxilla 1: inner plate very elongate, distally very narrow, with 2 stout setae in truly distal position; outer plate with 11 blade-shaped spines (in 7/4 arrangement), which are denticulate on one side; palp 2-articulate, broad with distal row of 12 cuspidate spines anteriorly followed by a stout antero-distal flag seta.

Maxilla 2: plates very narrow, tapering towards tip; inner plate much shorter and slightly narrower than outer plate.

Maxilliped: inner and outer plates well developed; inner plate narrow, about half the length of outer plate, with well-developed posteromedial row of strong setae, 3 apical nodular spines and 1 anterodistal stout seta; outer plate reaching tip of article 2 of palp, with lateral double row of long setae, 2 distal large stout blunt spines, a medial row of 22 much smaller low nodular spines, and 7 small slender isolated facial spines; dactylus well developed.

Gills: long accessory process on gill of pereopods 5–6; gill of pereopod 7 well developed and posteriorly pointed.

Oostegites: linear, from gnathopod 2 to pereopod 5.

Gnathopod 1: subchelate; coxa large but slightly shorter than coxa 2, externally visible, triangular, anterior and posterior margins nearly straight and strongly divergent, ventral margin broad and distinctly convex; all articles except merus and dactylus elongate; basis strongly convex anteriorly, weakly convex posteriorly, with many long setae along anterior margin, 3.0 x as long as wide; ischium linear, 6 x as long as wide; merus triangular, 3 x as long as wide, much shorter than ischium and carpus; carpus linear, 5 x as long as wide; propodus linear, 5.5 x as long as wide and as long as carpus, palm oblique and minutely denticulate; dactylus well developed.

Gnathopod 2: minutely chelate; coxa large but slightly shorter than coxa 3, subrectangular; ischium 3.4. x as long as wide; carpus 2.3 x as long as wide, 2.0 x as long as propodus, anterior margin with dense row of very short setae beyond midlength and many long setae distally; propodus strongly convex, anteriorly with many long setae, weakly concave posteriorly with many very short setae, palm with a cavity and an extended inner dentate basket; dactylus very short, denticulate, reaching corner of palm.

Pereopod 3: coxa large, about as long as coxa 4, subrectangular, with posterior margin slightly concave; ischium, merus and carpus with many long setae posteriorly; merus slightly expanded anteriorly, 2.8 x as long as wide; carpus 3.1 x as long as wide and 0.73 x as long as merus; propodus 5.4 x as long as wide, 1.3 x as long as carpus, with 10 well-developed spines (or pairs of spines), posteriorly, the largest spines of each group blunt-tipped and with accessory branch; dactylus normally developed, curved, with long unguis, 0.39 x as long as propodus.

Pereopod 4: coxa deeper than wide, posteroventral lobe large, posteroventral corner of lobe more or less rounded (with scarcely distinct angular discontinuity); ischium, merus and carpus with many long setae posteriorly; merus slightly expanded anteriorly, 2.6 x as long as wide; carpus 2.6 x as long as wide and 0.62 x as long as merus; propodus 4.7 x as long as wide, 1.3 x as long as carpus, with 10 well-developed spines (or pairs of spines) posteriorly, the largest spines of each group blunt-tipped and with accessory branch; dactylus normally developed, curved, with long unguis, 0.41 x as long as propodus.

Pereopod 5: coxa very slightly longer than broad, weakly bilobate, posterior lobe slightly produced ventrally, 1.6 x as long as basis; basis strongly expanded posteriorly, about as long as broad, with 14 short spines or groups of spines anteriorly, 7 very weak crenellations posteriorly, and well-developed broadly rounded posteroventral lobe; ischium with 4 groups of short spines anteriorly, the distal one associated with a long seta; merus expanded, 1.3 x as long as broad, anterior margin straight, posterior margin convex bearing 4 long setae and 1 distal medium-sized spine; carpus 2.0 x as long as broad, with 1 posterodistal short seta and 1 posterodistal spine of normal length and stoutness; propodus 4.8 x as long as broad, 1.5 x as long as carpus, with 7 blunt-tipped spines (or pairs of spines in which one is blunt-tipped) anteriorly, each spine with accessory branch (except those of distal pair); dactylus normally developed, curved, with long unguis, 0.40 x as long as propodus.

Pereopod 6: coxa slightly concave anteriorly, convex posteriorly, distinctly bilobed, shorter than coxa 5, 1.4 x as long as broad, 0.96 x as long as basis; basis longer than basis of pereopod 5, expanded posteriorly, 1.3 x as long as broad, with 11 short spines or groups of spines anteriorly, 11 very weak crenellations posteriorly, posteroventral lobe well-developed and broadly rounded; ischium–dactylus combined slightly longer than in pereopod 5 and as long as in pereopod 7; ischium with 4 short spines and 3 long setae on anterior margin; merus weakly expanded, 1.9 x as long as broad, anterior margin nearly straight, posterior margin weakly convex, bearing 4 isolated small spines of normal stoutness; carpus 2.6 x as long as broad, with 1 short seta and 1 spine of normal length and stoutness on posterodistal corner; propodus 5.6 x as long as broad, 1.5 x as long as carpus, with 9 blunt-tipped spines (or pairs of spines in which one is blunt-tipped) anteriorly, each spine with an accessory branch (except those of distal pair); dactylus normally developed, curved, with long unguis, 0.39 x as long as propodus.

Pereopod 7: coxa regularly rounded, shorter than coxa 6, slightly longer than broad, 0.5 x as long as basis; basis longer than basis of pereopod 6, expanded posteriorly, 1.4 x as long as broad, with 11 short spines or groups of spines anteriorly, 11 very weak crenellations posteriorly, posteroventral lobe low and broadly rounded; ischium with 4 groups of 1 or 2 short spines on anterior margin, without long setae; merus weakly expanded, 1.9 x as long as broad, anterior margin straight, posterior margin weakly convex, bearing 4 isolated small spines of normal stoutness; carpus 2.7 x as long as broad, with number and strength of anterior spines normal, with 1 short seta and 2 spines of normal length and stoutness on posterodistal corner and no other posterior spines; propodus 5.2 x as long as broad, 1.4 x as long as carpus, with 9 blunt-tipped spines (or pairs of spines in which one is blunt-tipped) anteriorly, each spine with an accessory branch (except those of distal pair); dactylus normally developed, curved, with long unguis, about 0.35 x as long as propodus (not perfectly levelled on illustration).

Epimeron 1: anteroventral corner subquadrate, not produced; posteroventral corner regularly rounded; ventral margin nearly straight; posterior margin strongly convex.

Epimeron 2: anteroventral corner rounded, posteroventral corner bluntly subquadrate; ventral margin straight [to slightly concave]; posterior margin straight.

Epimeron 3: posteroventral corner regularly rounded; ventral and posterior margins slightly convex.

Urosomite 1 with a deep dorsal depression flanked on each side by lateral carina and followed by a prominent dorsal hump which is bluntly angular posteriorly.

Uropod 1: peduncle 1.6 x as long as inner ramus, with 15 very small stout lateral spines and 23 medium-sized slender spines; outer ramus slightly longer than inner ramus, with 7 small lateral spines and no medial spines; inner ramus with 4 medium-sized lateral spines and 9 well-developed medial spines.

Uropod 2 [abnormal in specimen used for description and illustration: inner ramus unusually short, possibly broken and regenerated]: peduncle 1.5 x as long as inner ramus, with 8 small to very small stout lateral spines and 9 medium-sized slender spines (all spines on distal 0.4); outer ramus much longer than inner ramus, with 12 stout medium-sized lateral spines and no medial spines; inner ramus without notch, with 4 lateral spines and 8 medial spines, all medium-sized.

Uropod 3: peduncle ordinary, about 0.85 x as long as outer ramus; outer ramus article 1 with 6 lateral spines, 11 medial long plumose setae and 1 long slender distomedial spine, article 2 at least 0.21 x as long as article 1; inner ramus reaching about 0.9 of article 1 of outer ramus, with 3 lateral spines and long plumose setae all along medial margin, without apical setae.

Telson elongate, cleft 0.57 of length, each lobe with 1 apical spine paired or not with 1 small seta, and 5–6 dorsolateral spines which are not all in a row.

Complementary description. The female described above has the flagellum of antenna 1 incomplete and the rami of uropod 2 with abnormal relative proportions (they were possibly broken and regenerated). A complementary account is given of a male from the expedition ARC94, sta. NA62, King George Island, Admiralty Bay, 62°08'S 58°27'W, 470 m, RBINS, INV. 100969.

Antenna 1 a bit shorter than antenna 2; major flagellum 15-articulate, with calceoli, first article nearly 0.5 x as long as entire flagellum; accessory flagellum 6-articulate, article 1 elongate, slightly longer than 5 distal articles combined.

Antenna 2 about 0.2 x as long as body; peduncular articles 3 to 5 not enlarged, with brush of setae; flagellum with 29 articles, calceoli present.

Gnathopods similar to those of female, but setae of anterior border of basis of gnathopod 1 shorter.

Pereopods 3–7 very similar to females but number of spines slightly lower.

Epimeron 3 with posteroventral margin not perfectly rounded, with trace of angularity.

Uropod 1: peduncle 1.4 x as long as inner ramus, with 5 very small lateral spines and 17 medium-sized slender medial spines; outer ramus slightly longer than inner ramus, with 5 small lateral spines and no medial spines; inner ramus with 2 medium-sized lateral spines and 7 medium-sized medial spines.

Uropod 2: peduncle as long as inner ramus, with 5 small lateral spines and 5 medium-sized medial spines (all spines on distal 0.25); outer ramus 0.9 x as long as inner ramus, with 8 medium-sized lateral spines and no medial spines; inner ramus without notch, with 5 lateral spines and 8 medial spines, all medium-sized.

Uropod 3: peduncle ordinary, about 0.74 x as long as outer ramus; outer ramus article 1 with 5 lateral spines, 10 medial long plumose setae and 1 long slender distomedial spine, with article 2 distally very narrow, about 0.31 x as long as article 1; inner ramus reaching tip of article 1 of outer ramus, with 3 lateral spines and with long plumose setae all along its medial margin, without apical setae.

Telson : elongate, cleft for 0.58 of its length, each lobe with 1 apical spine paired with 1 small seta, and 4 dorsolateral spines which are all in a row or not.

Colour pattern. An unpublished photograph made by M. Rauschert and identified by him as P. coatsi was examined. It shows an amphipod with red eyes, but otherwise almost colourless except a trace of reddish pigmentation.

Size. 19 mm.

Distribution and depth range. Davis Sea, Enderby Land, South Georgia, South Shetland Islands, Weddell Sea, 50–2889 m ( De Broyer et al. 2007; Havermans et al. 2011). The records from Îles Kerguelen ( De Broyer 1983) are based on P. debroyeri and this might also be the case of those from Macquarie Island and Prince Edward Islands.

Biology. “The species was captured mainly in baited traps, wherein it can represent up to 96% of total number of amphipods, with a record of 24 560 specimens in one trap. The digestive tract content of all individuals analyzed (collected either by trawl or by trap) revealed only fragments of carrion, indicating that P. coatsi is a true necrophage” ( Dauby et al. 2001). The specimen dissected for study, which was a well-calcified female, had fully developed oostegites with setae and, at the same time, ovaries full of eggs. Female amphipods lay their eggs shortly after moulting and since the occurrence of setae on oostegites is a sign of fertile intermoult ( Bellan-Santini 1999). This suggests that the dissected specimen had previously laid a batch of eggs, which hatched before capture, and that a further batch of eggs was developing. If this assumption is correct, this would mean that P. coatsi is iteroparous, as it is the case for other ‘orchomenids’ (see e.g. Thurston 1979; Stockton 1982; Moore & Wong 1996).

Figures

FIGURE 2. Pseudorchomene coatsi (Chilton, 1912), female, 19 mm, habitus, ANT – XIX / 3 – 4 (ANDEEP I & II), sta. 0 83, West of Elephant Island.

FIGURE 3. Pseudorchomene coatsi (Chilton, 1912), female, 19 mm, ANT – XIX / 3 – 4 (ANDEEP I & II), sta. 0 83, West of Elephant Island. A, head with appendages; B, right A 1 in medial view; C, upper lip and epistome in frontal view; D, left half of lower lip; E, left Md; F, tip of left Md; G, tip of lacinia mobilis; H, right Md; I, tip of right Md; J, right Mx 1; K, tip of outer plate of right Mx 1 in medial view; L, right Mx 2; M, tip of right Mx 2.

FIGURE 4. Pseudorchomene coatsi (Chilton, 1912), female, 19 mm, ANT – XIX / 3 – 4 (ANDEEP I & II), sta. 0 83, West of Elephant Island. A, Mxp; B, distal half of right outer plate; C, tip of right inner plate.

FIGURE 5. Pseudorchomene coatsi (Chilton, 1912), female, 19 mm, ANT – XIX / 3 – 4 (ANDEEP I & II), sta. 0 83, West of Elephant Island. A, right Gn 1; B, left Gn 2; C, right P 3; D, right P 4; E, right P 5; F, right P 6; G, right P 7.

FIGURE 6. Pseudorchomene coatsi (Chilton, 1912), female, 19 mm, ANT – XIX / 3 – 4 (ANDEEP I & II), sta. 0 83, West of Elephant Island. A, tip of chela of right Gn 1; B, tip of chela of left Gn 2; C, propodus and dactylus of right P 3; distal spines of propodus of right P 3; E, distal half of right P 5; F, penultimate pair of spines of propodus of right P 5; G, distal half of right P 6; H, penultimate pair of pines of propodus of right P 6; I, P 7 distal half of right P 7; J, distal spines of propodus of right P 7.

FIGURE 7. Pseudorchomene coatsi (Chilton, 1912), female, 19 mm, ANT – XIX / 3 – 4 (ANDEEP I & II), sta. 0 83, West of Elephant Island. A, pleon; B, right U 1; C, right U 2; D, right U 3; E, telson and urosomite 3.

FIGURE 8. Pseudorchomene coatsi (Chilton, 1912), male, 16 mm ARC 94, NA 62, Admiralty Bay. A, anterior part of head, epistome and upper lip; B, left A 1 in medial view; C, left A 2 in lateral view; D, left Gn 1; E, tip of chela of left Gn 1 (setae of propodus not shown); F, 5 distal articles of left Gn 2; G, propodus and dactylus of left P 3; H, posterodistal spines of propodus of left P 3.

FIGURE 9. Pseudorchomene coatsi (Chilton, 1912), male, 16 mm ARC 94, NA 62, Admiralty Bay. A, distal half of left P 7; B, antepenultimate pair of spines of anterior border of propodus of left P 7; C, urosome and posterior part of pleonite 3; D, right U 1; E, left U 2; F, left U 3; G, telson.