Pseudorchomene Schellenberg 1926

Genus Pseudorchomene Schellenberg, 1926

Pseudorchomene Schellenberg, 1926: 295. — Lowry & Stoddart, 1983: 381.

Description. Body shape: typical lysianassoid facies.

Head: anterior lobe of head moderately produced and broadly rounded; eye large, pyriform, dark, with fully developed ommatidia.

Antenna 1: major flagellum with article 1 very elongate; accessory flagellum with 5–7 articles, of which the first is very elongate.

Mouthparts forming quadrate bundle.

Upper lip and epistome differentially produced, prominent, separate; upper lip distinctly overreaching epistome.

Mandible: elongate, with posteriorly directed opening; margins of this posterior opening prolonged by 3 processes or lobes: 1 upper and 2 lower ones; incisor process with smooth cutting edge; lacinia mobilis present on left side only, narrowly cylindrical (finger-like), slightly curved, distally slightly dilated and with dentiform processes; longitudinal group of 3 small raker spines and an elongated patch of short fine setae present between incisor and molar processes; molar process elliptic, broad to moderately narrow, triturative; molar process not distally followed by row of spines; lateral setigerous crest arising from proximal 0.2 or 0.3 of molar process; palp 3-articulate, attached midway, proximal to molar process (anteroproximal corner of article 1 of palp not reaching or just reaching proximal border of molar process); article 1 without setae, article 2 longest with row of strong distal and subdistal A2-setae, article 3 of palp about 4 x as long as wide, with 1–2 proximal A3-setae, a row of D3-setae on distal 0.7, with 2–4 E3-setae.

Maxilla 1: inner plate very elongate, distally very narrow, with 2–3 setae in truly distal position; outer plate with 11 blade-shaped denticulate spines (‘spine teeth’); palp 2-articulate, broad with distal row of 8–13 spines anteriorly followed by stout antero-distal seta; left and right palps similar but not identical.

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

Maxilliped: inner and outer plates well developed; inner plate narrow, reaching about half of outer plate, with well-developed posteromedial row of strong setae, with 3 nodular apical spines and 1 anterodistal stout seta; outer plate reaching or overreaching tip of article 2 of palp, with double row of anterior setae, with 2 large anterodistal elongated stout spines, with posterior row of much smaller low nodular spines, with small narrow posterofacial spines; dactylus well developed.

Coxae 1–4 longer than the depth of their corresponding pereonites, their lower profile forming a very even line.

Gnathopod 1: coxa large, visible, triangular, with anterior and posterior margin nearly straight and strongly divergent, with ventral margin broad and weakly convex; leg subchelate, palm oblique to transverse; proportions of ischium, merus, carpus and propodus very variable.

Gnathopod 2: propodus much shorter than carpus with anterior border strongly convex, with posterior border straight to slightly concave; minutely chelate.

Pereopod 4: coxa with well-developed and fairly broad posterior lobe.

Pereopod 5: coxa without umbo or carina, with posteroventral lobe very blunt; basis as broad as long, or broader than long, distinctly shorter than coxa.

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.

Epimeron 1: anteroventrally angular or produced.

Epimeron 3: posteroventrally rounded or weakly produced.

Urosomite 1: dorsal process rounded, anteriorly preceded on each side by dorsolateral carina.

Urosomite 3: sharp dorsolateral carina on each side.

Uropod 1: inner ramus about 0.6 x as long as peduncle.

Uropod 2: inner ramus not constricted.

Uropod 3: ordinary, with rami well developed, with outer ramus 2-articulate and longer than peduncle.

Telson: longer than broad, cleft more than half its length, with dorsolateral spines.

Type species. Orchomenopsis coatsi Chilton, 1912.

Composition. Pseudorchomene coatsi (Chilton, 1912); Pseudorchomene debroyeri sp. n.; Pseudorchomene lophorachis sp. n.; Pseudorchomene plebs (Hurley, 1965); Pseudorchomene rossi (Walker, 1903).

Putative synapomorphy. Coxa 1 triangular or adz-shaped.

Distribution. Circum-Antarctic and circum-sub-Antarctic.

Depth range. 0–2889 m.

PC-2609071 Pseudorchomene coatsi

PC-23110911 Pseudorchomene coatsi

PC-SS2889-4 Pseudorchomene coatsi

PC-2210079 Pseudorchomene coatsi

PC-08100715 Pseudorchomene coatsi

PC-SS2889-5 Pseudorchomene coatsi

PC-22100710 Pseudorchomene coatsi

PC-SS349 Pseudorchomene coatsi

PC-2609076 Pseudorchomene coatsi

PC-05100712 Pseudorchomene coatsi

100 PC-1909075 Pseudorchomene coatsi

PC-1809076 Pseudorchomene coatsi

77

85 PC-21090732 Pseudorchomene coatsi

100 Pn-WS847 Pseudorchomene lophorachis

Pn-0304072 Pseudorchomene lophorachis 80 Pn-SS1943 Pseudorchomene lophorachis

90 Pn-0510077 Pseudorchomene lophorachis

PD-22100714B Pseudorchomene debroyeri

47 100 PD-1105109 Pseudorchomene debroyeri

PD-08100720B Pseudorchomene debroyeri

PD-1105108 Pseudorchomene debroyeri

AR-I19 Pseudorchomene rossi

100

AR-1010076 Pseudorchomene rossi

AR-3110078 Pseudorchomene rossi

AP-08100722 Pseudorchomene plebs

100 AP-08100719 Pseudorchomene plebs

AP-0506081 Pseudorchomene plebs

100 AP-LB383 Pseudorchomene plebs

AP-SS270 Pseudorchomene plebs

AP-31100710 Pseudorchomene plebs

AP-2311099 Pseudorchomene plebs

AS-SS3408 Abyssorchomene scotianensis

0.02 FIGURE 1. Neighbour-joining tree with bootstrap values based on the COI sequences.

Biology. Opportunistic or exclusive scavengers (Dauby et al. 2001). All species enter baited traps, which can capture up to thousands of specimens. They have been observed in benthic (Rakusa-Suszczewski 1982), pelagic (Hopkins 1987) and sympagic conditions (Kaufmann et al. 1993, 1995). Females are iteroparous, at least P. debroyeri (present data).

Remarks. Molecular analyses recovered the species P. coatsi, P. lophorachis, P. debroyeri, P. ro s s i and P. plebs as a monophyletic group, which is separated by a minimum genetic distance of 15.6 % from the specimen of Abyssorchomene scotianensis (Fig. 1). This species indeed belongs to a distinct clade, identified by Havermans et al. (2010), comprising the abyssal Abyssorchomene species. The monophyly of each species was confirmed and bootstrap values gave significant support to each species cluster. Specimens of P. lophorachis and P. debroyeri were separated from P. coatsi by a minimum divergence of 5.7 % and 7.9 %, respectively. Both newly described species were separated by a minimum 7.8 % sequence divergence. The intraspecific variation did not exceed 1.1 % for P. debroyeri and 0.3 % for P. lophorachis. These aspects are treated more extensively in the discussion.