Pseudorchomene lophorachis, D’Acoz, Cedric D’Udekem & Havermans, Charlotte, 2012

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 : 28-36

Pseudorchomene lophorachis sp. n.

( Figs 17–22 )

Type material. 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 HOLOTYPE [sex undetermined (sex detemination impossible without full dissection); no oostegites observed, 14.5 mm, right gnathopod 1 and left uropod 1 dissected but not mounted] stored in 96% ethanol, RBINS, INV. 100954, Specimen (HOLOTYPE) Id with corresponding Gen- Bank Accession number: Pn–WS847 ( GU109238 ) — 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 PARATYPE [sex undetermined (sex detemination impossible without full dissection); no oostegites observed, stored in 96% ethanol, RBINS, INV. 10954. — R/V “Polarstern” cruise ANT–XXII/3 (ANDEEP III), South of South Orkney Islands, sta. 150–7, 61°48’S 47°27’W, 1943 m, Agassiz trawl, 20.iii.2005: 1 female PARATYPE, 18 mm, stored in 96% ethanol., Specimen Id with corresponding GenBank accession number: Pn–0304072 ( HM054054 ) [ZMH-43141]. — R/V “Polarstern” cruise ANT–XXII/3 (ANDEEP III), South of South Orkney Islands, sta. 150–7, 61°48’S 47°27’W, 1943 m, Agassiz trawl, 20.iii.2005: 4 PARATYPES stored in 96% ethanol and 1 PARATYPE dissected and mounted on 15 slides in Euparal [ZMH-43142], 10 PARATYPES, Specimen Ids with corresponding GenBank accession numbers: Pn–0510077 ( HM054055 ), Pn–SS1943 ( GU109253 ) [ZMH-43143].

Type locality. South of South Orkney Islands, 61°48’S 47°27’W, 1943 m.

Etymology. Lophorachis is a noun in apposition formed by combining the Greek nouns λόφος, hill, and ραχɩς, backspine. The name refers to the low posterodorsal protuberances of the body segments.

Diagnosis. Somites of pereon and pleosome with small posterior humps. Mandibular palp inserted well proximal to molar process. Molar process broad. Gnathopod 1: basis anterior margin convex, palm oblique, basis 3.5 x, ischium 9 x, merus 7 x, carpus 7.5 x, propodus 8.5 x as long as wide. Gnathopod 2: carpus 2.3 x as long as wide. Pereopod 3: propodus with about 11 spines or pairs of spines (which are well developed). Pereopod 3–7: on propodus, broadest spine of each pair or triplet acute. Coxa 4 rounded posteroventrally. Pereopod 5: coxa very 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; 1.8; 1.9. Ratio length/width of carpus of pereopod 5–7: 1.8; 2.4; 2.3. Posterodistal angle of carpus of pereopod 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 posteriorly regularly rounded. Uropod 3 with medial margin of both rami with many long setae, with inner ramus not reaching tip of article 1 of outer ramus.

Description. Based on PARATYPES from R/V “Polarstern” cruise ANT–XXII/3 (ANDEEP III), South of South Orkney Islands, sta. 150–7, 61°48’S 47°27’W, 1943 m.

Body without dorsal carina; somites of pereon and pleosome with small posterior humps. 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, distinctly concave anteriorly, nearly straight posteriorly, dark, with fully developed ommatidia.

Antenna 1 slightly shorter than antenna 2; major flagellum 13-articulate, with first article 0.4 x as long as entire flagellum; accessory flagellum 5-articulate, with article 1 elongate, slightly longer than sum of 4 distal articles combined.

Antenna 2 about 0.1 x as long as body; peduncular articles 3 to 5 not enlarged, with brush of setae; flagellum 27-articlulate; calceoli absent.

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, slightly dilated distally with 3 dentiform processes (1 strong and 2 weak); 3 small raker spines and a elongate 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 12 strong distal and subdistal A2-setae, article 3 of palp 0.65 x as long as article 2, 4.2 x as long as wide, with 2 proximal A3-setae, a row of 22 D3-setae on distal 0.6 (these setae are shorter than width of article 3), and 2 E3-setae.

Maxilla 1: inner plate very elongate, very narrow distally, 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 9 cuspidate spines anteriorly followed by a stout antero-distal flag seta.

Maxilla 2: plates very narrow, tapering; 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, with 3 apical nodular spines and 1 anterodistal stout seta; outer plate reaching tip of article 2 of palp, with lateral double row of medium setae, 2 distal large stout blunt spines, a medial row of 19 much smaller low nodular spines, and 8 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, with anterior and posterior margins weakly concave and strongly divergent, ventral border broad and weakly convex; all articles except dactylus extremely elongate; basis anteriorly strongly convex and posteriorly straight, with many long setae along anterior margin, about 3.5 x as long as wide; ischium linear, 9 x as long as wide; merus linear, 7 x as long as wide, slightly shorter than ischium and as long as carpus; carpus linear, 7.5 x as long as wide; propodus linear, 8.5 x as long as wide and slightly shorter than carpus, palm oblique and minutely denticulate; dactylus well developed.

Gnathopod 2: minutely chelate coxa large but slightly shorter than coxa 3, subrectangular; ischium 3.7 x as long as wide; carpus 2.3 x as long as wide, 2.2 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, straight 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, posterior margin slightly concave; 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 0.67 x as long as merus; propodus 4.9 x as long as wide, 1.4 x as long as carpus, with 11 well-developed spines (or pairs of spines) posteriorly, the largest spines of each group acute and with accessory branch; dactylus normally developed, curved, with long unguis, 0.41 x as long as propodus.

Pereopod 4: coxa deeper than wide, posteroventral lobe large, posteroventral corner of lobe regularly rounded (without angular discontinuity); ischium, merus and carpus with many long setae posteriorly; merus slightly expanded anteriorly, 2.4 x as long as wide; carpus 2.0 x as long as wide and 0.56 x as long as merus; propodus 4.6 x as long as wide, 1.4 x as long as carpus, with 11 well-developed spines (or pairs of spines) posteriorly, the largest spines of each group acute and with accessory branch; dactylus normally developed, curved, with long unguis, 0.39 x as long as propodus.

Pereopod 5: coxa very slightly longer than broad, weakly bilobate, posterior lobe slightly produced ventrally, 1.5 x as long as basis; basis strongly expanded posteriorly, about as long as broad, with 10 short spines or groups of short spines anteriorly, 6 very weak crenellations posteriorly, each associated with tiny setule, posteroventral lobe well developed and broadly rounded; ischium with 3 anterior groups of short spines, the distal one associated with long seta; merus expanded, 1.3 x as long as broad, anterior margin straight, posterior margin rounded, bearing 5 long setae and 1 distal medium-sized spine; carpus 1.8 x as long as broad, with 2 posterodistal spines of normal length and stoutness; propodus 4.2 x as long as broad, 1.4 x as long as carpus, with 6 pairs of acute spines anteriorly, each spine with an accessory branch (except those of distal pair); dactylus normally developed, curved, with long unguis, 0.42 x as long as propodus.

Pereopod 6: coxa anterior margin slightly concave, posterior margin convex, weakly bilobed, shorter than coxa 5, 1.6 x as long as broad, 0.9 x as long as basis; basis longer than basis of pereopod 5, expanded posteriorly, 1.4 x as long as broad, with 9 short spines or groups of short spines anteriorly, 8 very weak crenellations posteriorly, each associated with tiny setule, posteroventral lobe well-developed, broadly rounded; ischium–dactylus combined slightly longer than in pereopod 5 and as long as in pereopod 7; ischium with 4 anterior groups of articulated structures including a short spine and/or a long seta; merus weakly expanded, 1.8 x as long as broad, anterior margin straight, posterior margin weakly curved, bearing 6 isolated small spines of normal stoutness; carpus 2.4 x as long as broad, with 1 short seta and 2 spines of normal length and stoutness on posterodistal corner; propodus 4.8 x as long as broad, 1.4 x as long as carpus, with 9 acute spines (or pairs of spines) 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, as long as 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 14 short spines or groups of short spines anteriorly, 10 very weak crenellations posteriorly, most associated with tiny setule, 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 7 isolated small spines of normal stoutness; carpus 2.3 x as long as broad, with number and strength of anterior spines normal, with 3 posterodistal spines of normal length and stoutness and no other posterior spines; propodus 4.6 x as long as broad, 1.4 x as long as carpus, with 9 acute spines (or pairs of spines) anteriorly, each spine with an accessory branch (except those of distal pair), without posterior spines; dactylus normally developed, curved, with long unguis, 0.36 x as long as propodus.

Epimeron 1: anteroventral corner subquadrate, slightly produced; posteroventral corner regularly rounded; ventral margin straight; posterior margin slightly convex.

Epimeron 2: anteroventral corner very broadly angular, posteroventral corner bluntly subquadrate; ventral margin 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 regularly rounded dorsal hump.

Uropod 1: peduncle 1.5 x as long as inner ramus, with 12 small stout lateral spines and 16 medium-sized slen- der spines; outer ramus almost as long as inner ramus, with 7 stout and medium-sized lateral spines and no medial spines; inner ramus with 3 lateral spines and 9 medial spines, all medium-sized.

Uropod 2: peduncle 1.2 x as long as inner ramus, with 7 small to very small stout lateral spines and 6 mediumsized slender spines (all spines on distal 0.3); outer ramus 0.9 x as long as inner ramus, with 10 stout and mediumsized lateral spines and no medial spines; inner ramus without notch, with 5 lateral spines and 10 medial spines, all medium-sized.

Uropod 3: peduncle ordinary, 0.78 x as long as outer ramus; outer ramus with article 1 with 6 lateral spines, 9 medial long plumose setae and distomedial spine, with article 2 0.13 x as long as article 1; inner ramus reaching 0.85 of article 1 of outer ramus, with 5 lateral spines, long plumose setae all along medial margin and 2 apical setae.

Telson : elongate, cleft for 0.57 of its length, each lobe with 1 apical spine paired with 1 small seta, dorsolateral spines.

Colour pattern. Unknown.

Size. 18 mm.

Distribution and depth range. Scotia Sea and Weddell Sea, 847–1943 m.

Biology. Carrion is part of the diet of the species since specimens were captured occasionally by means of fish traps, but it is not known if it is an obligatory or a facultative scavenger. The remarkably elongated gnathopod 1 (even more elongated than in P. coatsi and P. debroyeri ) might suggest a specialized feeding behaviour.

Remarks. Pseudorchomene lophorachis is similar to P. coatsi and P. debroyeri but has the first gnathopod characterized by an elongated and slender ischium, merus and carpus, while only the ischium and carpus are elongate in the two other species. P. lophorachis bears rounded dorsal humps, which are absent in P. coatsi and P. debroyeri .

The holotype deposited at the Royal Belgian Institute of Natural Sciences is identical to the illustrated specimens: it has small posterodorsal humps on body segments, coxa 1 is adz-shaped, and gnathopod 1 is immensely elongated.

Figures

FIGURE 17. Pseudorchomene lophorachis sp. n., paratype, female, 18 mm, habitus, ANT – XXII / 3, sta. 150, S of South Orkney Islands.

FIGURE 18. Pseudorchomene lophorachis sp. n., paratype, female, 18 mm, ANT – XXII / 3, sta. 150, S of South Orkney Islands. A, head with appendages; B, left antenna in medial view; C, right Md; D, tip of right Md; E, tip of left Md; F, lacinia mobilis; G, left Mx 1; H, tip of left Mx 1; I, tip of right Mx 1; J, right Mx 2; K, tip of right Mx 2.

FIGURE 19. Pseudorchomene lophorachis sp. n., paratype, female, 18 mm, ANT – XXII / 3, sta. 150, S of South Orkney Islands. A, Mxp (left inner plate not shown); B, left outer plate; C, right inner plate.

FIGURE 20. Pseudorchomene lophorachis sp. n., paratype, female, 18 mm, ANT – XXII / 3, sta. 150, S of South Orkney Islands. A, left Gn 1; B, left Gn 2; C, right P 3; D, right P 4; E, left P 5; F, left P 6; G, left P 7.

FIGURE 21. Pseudorchomene lophorachis sp. n., paratype, female, 18 mm, ANT – XXII / 3, sta. 150, S of South Orkney Islands. A, tip of chela of left Gn 1; B, tip of chela of left Gn 2; C, propodus and dactylus of right P 3; D, distal spines of propodus of right P 3; E, distal half of left P 5; F, penultimate pair of spines of propodus of left P 5; G, distal half of left P 6; H, penultimate pair of spines of propodus of left P 6; I, distal half of left P 7; J, distal spines of left P 7.

FIGURE 22. Pseudorchomene lophorachis sp. n., paratype, female, 18 mm, ANT – XXII / 3, sta. 150, S of South Orkney Islands. A, pleon; B, left U 1; C, right U 2; D, left U 3; E, telson.