Abyssorchomene scotianensis

Abyssorchomene scotianensis (Andres, 1983)

Figs 18–25

Orchomene scotianensis Andres, 1983: 205–212, figs 10–12.

Orchomenopsis chilensis f. abyssorum Schellenberg, 1926: 291–292, fig. 27.

Orchomenella abyssorum – Barnard K.H. 1932: 69, figs 27b, 28 (= Abyssorchomene cf. scotianensis , except fig. 27b = Abyssorchomene abyssorum). — Nicholls 1938: 35, fig. 15 (= Abyssorchomene cf. scotianensis). — Dahl 1954: 282 (= Abyssorchomene cf. scotianensis). — Birstein & Vinogradov 1962: 41 (= Abyssorchomene cf. scotianensis).

Orchomene abyssorum – Arnaud 1974: 572 (ecology). — Lowry & Bullock 1976: 94–95 (in part). — Lowry 1982: 320. — Wakabara et al. 1990: 2, 4, 6 (= Abyssorchomene cf. scotianensis). — Barnard & Karaman 1991: 508 (in part).

Abyssorchomene abyssorum – De Broyer 1983: 142–144 (in part). — De Broyer & Jażdżewski 1993: 64. — De Broyer et al. 1999: 166; 2001: 746, 749 (ecology); 2004: 1742, table 4 (ecology); 2007: 163. — Havermans et al. 2010: 204–207; 2011: 232, 235. — Havermans 2012: 96, 99–101, 104, 106–107, 116, 122, 156, 181, 195–196, 215, 226, 250–251, 260, 262.

Orchomene (Abyssorchomene) abyssorum – Barnard & Ingram 1990: 26 (in discussion = in part).

Orchomene sp. “L-shaped eye” – d’Udekem d’Acoz & Robert 2008: 51, 54.

Abyssorchomene “L-shaped eye”, Abyssorchomene cf. scotianensis – Havermans et al. 2012: 36, 39.

Abyssorchomene sp. n. aff. scotianensis – d’Udekem & Havermans 2012: fig. 31.

New diagnosis

Pereonites 1–7 and pleonites 1–2 smooth, without any dorsoposterior humps. Lateral cephalic lobe broadly rounded, dorsal and ventral margins regularly and nearly equally convex. Antennae 1–2 of male with calceoli, female without. Epistome weakly but distinctly protruding in front of upper lip (or level with upper lip). Maxilla 1 palp distal end strongly convex, with conical distal spines not contiguous. Maxilliped inner plate, distal margin regularly beveled, very slightly concave, with mediodistal extension slightly surpassing the level of the outer corner; outer plate inner margin weakly scalloped. Coxa 1 distinctly widened, distal width ~ 1.4 × proximal width. Gnathopod 2 propodus of female slender, length ~3 × width (similar in form to male), dactylus small, inserted in the middle of the distal margin, lacking a palm concavity. Coxa 5 slightly but distinctly posterolobate, posterior lobe irregularly convex, with distal half of posterior margin nearly straight. Pereopod 7 basis, distal third of posterior margin with a straight bevel. Uropod 1 peduncle length ~ 1.6 × length of outer ramus. Uropod 3 inner ramus barely reaches (or very slightly exceeds) distal end of article 1 of uropod 3 outer ramus. Telson cleft ~ 50% in female, more deeply cleft (up to 60%) in male.

Material examined

Paratypes SCOTIA SEA • 1 ♀ (9.0 mm), 1 juvenile (2.7 mm); FFS Walther Herwig, station 210, Hol 239; 63°22′ S, 054°10′ W; depth 0–223 m (bottom depth 235 m); gear, Rectangular Midwater Trawl (RMT) 1+ 8; 13 Jan. 1978; A. Baker and F. Nast leg.; ZMH K 32 401.

Additional material

WESTERN WEDDELL SEA • 1 ♀ (mature, 12 mm, figured, appendages on 2 slides); off East Peninsula, Larsen B; RV Polarstern ANT XXIII-8 (IPY-CAML), station PS69-706-7; 65°26.57′ S, 061°26.82′ W; depth 828 m; gear, fish traps; 15 Jan. 2007; C. d’Udekem d’Acoz and H. Robert leg.; CMNC 2022-0005 • 1 ♀ (9.5 mm, head figured); same collection data as for preceding; CMNC 2022-0006 • ♂ (12.4 mm, figured, appendages on 2 slides); same collection data as for preceding; CMNC 2022-0007 • 9 ♂♂ (8–11 mm); same collection data as for preceding; RBINS INV. 138.498 • 2 ♂♂, 2 ♀♀, 2 juveniles; same collection data as for preceding; RBINS INV. 138.490 • 1 ♂, 1 ♀; same collection data as for preceding; RBINS INV. 138.493 • 51 specs (♀ up to 11.4 mm); same collection data as for preceding; RBINS INV. 138.494 • 50 specs (♀ up to 11.0 mm); same collection data as for preceding; CMNC 2022-0008.

ROSS SEA • 2 ♂♂ (8.6 mm, 5.5 mm), 2 ♀♀ (5.8 mm, 5.5 mm); Ross Ice Shelf, station J9; 82°22′30″ S, 168°37′33″ E; depth 600 m (under ice 415 m thick); gear, baited traps; 7–29 Dec. 1977; T. DeLaca and W.L. Stockton leg.; RBINS INV. 138.495. See Stockton & DeLaca (1982).

SOUTHERN OCEAN • 3 ♂♂ (10–13.1 mm); Oates Coast, off Oates Land; RV Ob, 3 rd Soviet Antarctic Expedition. (SAE 3), station 337; 69°48′ S, 161°49′ E; depth 1040 m; 10 Feb.1958; A.P. Andriashev (Zoological Institute Russian Academy of Sciences, St. Petersburg).

AMUNDSEN SEA • 1 ♀ (10 mm, with 13 advanced stage embryos), 1 ♀? (5.7 mm), ♂ (5.8 mm); RRS James Clark Ross, JR 179, BIOPEARL II, station BIO5-EBS-2A; 73°52'55" S, 106°18'33" W; depth 1113 m; gear, epibenthic sledge; 9 Mar. 2008; K. Linse (British Antarctic Survey, Cambridge).

Description

Based on female (mature), 12 mm (CMNC 2022-0005); paratype female, 9 mm, (not illustrated, ZMH K 32 401) and on remaining material described by Andres (1983).

PEREONITES 1–7 AND PLEONITES 1–2 (Fig. 18). Body smooth, without dorsoposterior hump on each segment.

PLEONITE 3 (Figs 18–19). With a distinct, rounded posterodorsal elevation slightly overhanging urosomite 1.

COXAE 1–2 (Figs 18–19). Subequal to slightly longer (1.1 ×) than corresponding pereonites.

COXAE 3–4 (Fig. 18). Slightly longer (1.2×) than corresponding pereonites.

EPIMERON 3 (Figs 18–19). Subquadrate, with posterior margin weakly convex, posteroventral corner broadly rounded, with angle slightly obtuse, ventral margin regularly convex.

UROSOMITE 1 (Fig. 19). With a deep, dorsal concavity in front of the strongly, regularly rounded upright dorsal boss, convex on posterior margin, and slightly overhanging urosomite 2.

HEAD (Fig. 19). About equal in length to pereonite 1.

LATERAL CEPHALIC LOBE (Fig. 19). Broadly rounded, dorsal and ventral margins regularly and nearly equally convex.

EYE (Fig. 19). Non ommatidial, formed of pigment granules; large, crescent-shaped or L-shaped, parallel to front head margin, length about 70% of the head height (note: see p. 26, 34 for comments on evaluating eye size/shape).

ANTENNA 1 (Fig. 19). Peduncular article 1 dilated (length 1.2 × width), without anterodistal lobe; flagellum article 1 about half length of peduncular article 1, callynophorate, densely furnished medially with double row of aesthetascs; accessory flagellum 5-articulate, first article long, about equal to the remaining articles combined; flagellum 13-articulate, calceoli absent.

ANTENNA 2 (Fig. 19). Slightly longer (1.2 ×) than antenna 1; geniculate between peduncular articles 3–4, peduncular articles 4–5 lined with anteromedial brush setae, peduncular article 5 short, length 0.66 × article 4; flagellum 18-articulate, calceoli absent.

EPISTOME (Fig. 19). Level with or very slightly protruding in front of weakly rounded upper lip, forming straight anterior margin and cephalic ridge, separated from upper lip by a small slit.

MANDIBLE (Fig. 20). Incisor strongly convex, slightly widened; left lacinia mobilis curved, with 2 strong apical teeth and 1 subapical tooth, right lacking; accessory spine row with 3 strong spines, interspersed with fine setae; molar forming a narrow crest, somewhat falciform, acutely produced on proximal end, setose with mixed ornamentation, distal half or third setiferous, proximal half or two-thirds forming a reduced, ridged triturative surface, hairy process located proximal to molar; palp attached proximal to molar, article 2 1.8× length of article 3, with 24–25 A2-pectinate setae, article 3 weakly falciform, 0.55 × length of article 2, with 3 A3-seta, 26 D3-pectinate setae and 2 E3-setae.

LOWER LIP (Fig. 20). Outer lobes broad with inner margins strongly setose, distal margins excavate, without inner lobes, mandibular lobes narrow.

MAXILLA 1 (Fig. 21). Inner plate with short, rounded, apical projection slightly surpassing the basal insertion of two (or three) apical plumose setae of unequal size; outer plate with 11 strong spine-teeth in 7/4 crown arrangement; palp article 2 slightly widened at distal two-thirds, distal margin strongly convex, with 7–9 non-contiguous conical apical spines, and a thin spine on outer corner.

MAXILLA 2 (Fig. 21). Outer and inner plates not slender, tapering distally, both with strong rows of pectinate medial marginal spines and setae; inner plate much shorter than outer plate, with marginal setae on the distal third of the inner margin, distal end of inner plate slightly surpassing the proximal end of setal row of outer plate.

MAXILLIPED (Fig. 21). Inner plate subrectangular, extending slightly past the distal end of the inner margin of palp article 1 and reaching about one-third length of outer plate, distal margin regularly bevelled, very slightly concave, with mediodistal extension slightly surpassing the level of the outer corner; with 3 embedded nodular spines unequally spaced, the two mediodistal marginal nodular spines situated close to each other with the corner one more protruding, the third one located closer to the outer margin corner, plumose setae inserted along medial margin and inner part of distal margin; outer plate subovate, length 1.66 × width, not reaching distal end of palp article 2, with two dissimilar apical spines and numerous (11) embedded, medial nodular spines, medial margin weakly scalloped; palp 4-articulate, strongly setose medially, dactylus well developed, about 0.7 × length of article 3, distal inner margin with 2–3 short setae.

GNATHOPOD 1 (Fig. 22). Coxa distinctly widened, distal width 1.43 × proximal width and about 78% of length, anterior margin weakly concave, anterodorsal corner broadly rounded, posterior margin nearly straight, distal margin strongly convex in anterior half, slightly convex in posterior half, posteroventral corner not narrowly rounded; basis moderately stout, width about one third of the length and slightly narrower than propodus, anterior margin with numerous long and short setae; ischium subequal to merus, both with posterior margins setose; carpus short, compressed, length about 0.5 × propodus, with narrow, setose posterodistal lobe, not guarding the hind margin of propodus; propodus subchelate, subrectangular, with anterior margin weakly convex, posterior margin nearly straight; palm transverse, very slightly convex, microcrenulate and adorned with small setae, palm corner with 2 blunt protrusions and defined by 1 medial and 1 lateral spine; dactylus subequal to palm or barely overriding palmar corner.

GNATHOPOD 2 (Fig. 23). Coxa subrectangular, length 2.4 × width; basis elongated, distal third slightly curved, length 6.8× width; ischium length 3× width; carpus about 2× length of propodus, distoventrally with subtriangular scales; propodus chelate, slender, slightly widened distally, length 3× width, and much narrower, about 60% of the carpus width, surface finely setose with distal groups of long pectinate setae, dorsal margin convex, hind margin weakly concave, palm not excavate, with a narrow gap, with a small setal basket on distal third and ending in a tooth-like denticulate projection and a strong subapical seta; dactylus fitting palm, inner margin bearing distally a spiny protuberance fitting to the palm and weakly denticulate projection.

PEREOPOD 3 (Fig. 24). Coxa subrectangular, with anterior margin slightly convex, posterior margin slightly concave, ventral margin very slightly convex, length 2.45 × width; posterior margins of ischium-merus with clusters of long setae, rest of pereopod like pereopod 4.

PEREOPOD 4 (Fig. 24). Coxa length 1.42 × width, width 0.7× length, anterior margin convex, posterior margin deeply excavate, with wide subtriangular, posterodistal lobe, corner with subquadrate angle, located at distal 63% of the coxa length; ventral margin evenly convex; posterior margins of ischiumcarpus with clusters of long setae; propodus with about 7 short spine groups; dactylus 0.4× length of propodus.

PEREOPOD 5 (Fig. 24). Coxa slightly but distinctly posterolobate, posterior lobe irregularly convex, with distal half of posterior margin nearly straight, width 1.14 × length; basis longer (1.2 ×) than wide, slightly narrowing distally, anterior margin nearly straight, with small spines, posterior margin convex, very weakly serrate, posterodistal lobe surpassing distal margin of ischium; merus weakly expanded (width 0.65× length), longer than carpus and bearing anterior and posterior long setae; carpus with anterior marginal setae; propodus narrow, shorter than merus-carpus, with 6–7 anterior marginal short spine groups; dactylus short, 0.36× length of propodus.

PEREOPOD 6 (Fig. 24). Basis long, length 1.45 × width, anterior margin nearly straight, with small spines, posterior margin hardly serrate, slightly narrowing distally, posterodistal lobe not reaching distal margin of ischium; merus very weakly expanded (width 0.48 × length) and bearing anterior marginal long setae and few short slender posterior spines; propodus shorter than length of merus-carpus, anterior margin with 7–8 clusters of short spines, dactylus 0.34× length of propodus.

PEREOPOD 7 (Fig. 24). Coxa subovate, rounded behind; basis proximal two-thirds subrectangular, anterior margin slightly concave, with small spines, distal third of posterior margin with a straight bevel, with about 9 weak serrations, posterodistal lobe not extending to distal margin of ischium; merus not expanded (narrower than in P6), anterior margins of merus-carpus with short spine groups, posterior margin bearing few short slender spines; propodus shorter than merus-carpus, dactylus broken.

UROPOD 1 (Fig. 25). Peduncle about 1.57 × length of outer ramus and 1.73× inner ramus, dorsolateral and dorsomedial margins spinose; inner ramus shorter and more spiniferous than outer ramus; outer ramus medial margin lacking spines.

UROPOD 2 (Fig. 25). Peduncle about 1.2× length of outer ramus, dorsolateral and dorsomedial margins each with 4 spines; inner ramus slightly shorter than outer ramus, length 0.92×, with 2 dorsolateral and 6 dorsomedial marginal spines; outer ramus with 7 closely spaced slender spines on dorsolateral margin, dorsomedial margin lacking spines.

UROPOD 3 (Fig. 25). Peduncle 0.94 × length of biarticulate outer ramus; second article of outer ramus 0.4× length of article 1; inner ramus barely reaching or very slightly extends past distal end of article 1 of outer ramus, inner margins of rami with long plumose setae and outer margins with a few slender spines.

TELSON (Fig. 25). Length subequal to uropod 3 peduncle, 1.5 × longer than wide, cleft (50%), lobes tapering distally with 3–4 submarginal spines and 1 distal spine set in middle of lobe tip.

GILLS 5–6 (Fig. 24). With 1 long, tubular accessory lobe on gill 5 and 2 lobes on gill 6, both inserted basally.

GILL 7 (Fig. 24). Present, small.

BROOD PLATES (Figs 23–24). Present on gnathopod 2 and pereopods 3–5, long, slender and curved distally, largest on gnathopod 2 and pereopods 3–4, smallest on pereopod 5, with long curved brood setae ranging in number from ~ 10–20.

STOMODEUM. Extending to the 7 th pereonite.

Male (based on: Andres (1983), ANT XXIII-8, station 706 and SAE 3 material)

Similar to female, but differing as follows:

BODY (Fig. 18). Larger but slightly less robust.

LATERAL HEAD LOBE (Fig. 19). Slightly narrower distally, subtriangular, ventral margin less convex.

EYE (Figs 18–19). More strongly developed, extending to 66–80% of the head height.

ANTENNA 1 (Figs 18–19). Callynophore much stronger, subequal in length to peduncular article 1, flagellum 12–17-articulate, articles broader, calceoli present (callynophore size is related to maturity of male, terminal males have the largest callynophore and greater number of flagellar articles).

ANTENNA 2 (Fig. 18). Peduncular articles 4–5 slightly broader; flagellum 15–23-articulate, with calceoli.

MANDIBLE. Palp article 3 proportionally longer, length 0.65 × article 2.

MAXILLA 1 (Fig. 21). Inner plate, distal projection subacute; palp article 2 strongly widened at distal twothirds, with (according to size) 5–12 non-contiguous, conical apical spines.

GNATHOPOD 1. Coxa slightly less widened distally than in female, length 1.34× width, anteroventral corner more narrowly rounded, posterior margin slightly concave; basis, anterior margin with scattered short setae.

GNATHOPOD 2 (Fig. 22). Propodus similar to female, except anterodistally narrower and merging smoothly with dactyl insertion on dorsal margin.

COXA 4 (Fig. 24). Distinctly narrower than in female, length about 1.76 × width, posterior excavation shallower, posterior lobe smaller with subquadrate angle located at about 60% of the length.

PEREOPOD 5. Merus slightly more expanded.

UROPOD 2 (Fig. 25). Inner ramus distinctly shorter than outer; outer ramus with 15 lateral marginal spines of differing morphology, distolateral spines stouter, bluntly rounded and more closely spaced than proximal ones, which are thin and acute (number of spines is size related, but males of equal size to females have greater number of spines and always possess the two different types of spines, see p. 24).

UROPOD 3 (Fig. 25). Inner ramus slightly longer than peduncle; second article of outer ramus about 0.33–0.5× the length of article 1.

UROSOMITE 1 (Figs 18–19). Boss strong, anterodorsal and posterior margins straighter, slightly more pointed and slightly more projecting backward.

TELSON. Slightly narrower and longer, length 1.75× width; cleft slightly deeper, about 55–60% of its length.

Ontogenic variations

Andres (1983) collected a very large male (16 mm) and noticed on maxilla 1 that the width of palp article 2 increases in size as well as the number (as usual) of apical spines (from 5 in the holotype male, 9.5 mm, to 8 in the 13 mm female and 12 in the 16 mm male; see Andres’ 1983: fig. 10). On the maxilliped outer lobe of the 16 mm male, he noted the presence of 4 apical stout spines instead of the usual 2 stout spines, as well as the presence of setae on the inner margin of the dactylus in the palp of larger specimens. As well, he remarked on the stronger development of the gnathopod 2 palm and dactylus spines and setae in the largest specimens. He also showed that the length of the second article of uropod 3 outer ramus reaches 0.34× the length of article 1 in the largest male, instead of about 0.5× the length in the smaller, 9.5 mm holotype (see Andres’ 1983: fig. 12).

Distribution

Southern Ocean: Scotia Sea (Andres 1983); Wilhelm II coast (Schellenberg 1926); Weddell Sea (De Broyer et al. 1999, 2001, 2004, 2006, 2007; d’Udekem d’Acoz & Robert 2008; d’Udekem d’Acoz & Havermans 2012); Amundsen Sea (this paper); Ross Sea (this paper); off Oates Land (this paper).

Depth range

Bottom records: possibly 60 m? (Wakabara et al. 1990), depth 385 m (Schellenberg 1926) to 3070 m (De Broyer et al. 2004).

Pelagic records: possibly 0 to 430 m above bottom (Andres (1983). See remark (p. 24) on pelagic occurrence under A. abyssorum.

Remarks

As discussed by Andres (1983), the juvenile Antarctic specimens identified as Orchomenopsis chilensis f. abyssorum by Schellenberg (1926) may be attributed to Abyssorchomene scotianensis. The peculiar shape of the maxilla 1 palp article 2 figured by Barnard (1932) (Fig. 28) also indicates that this material may belong to A. scotianensis, but the presence of the “large yellowish brown pear-shaped” eyes should be confirmed first. Andres (1983) also described “extended pear-shaped” (“ gestreckt birnenförmige Augen ”) and Nicholls (1938) (Fig. 15) illustrated a “large, faded brown”, typically pear-shaped eye, although he recognized that his material had undergone a considerable degree of maceration. We never noticed pearshaped eyes among the abundant material we identified. Indeed, specimens we examined showed the typical, large “L-shaped eyes”, with larger males having larger eyes (see Figs 18–19). As previously noted (p. 34), eye shape and size are best recognized in freshly collected specimens. Over long periods of time in alcohol preservation, colour pigments fade and are lost, causing the eyes to become extremely difficult to ascertain. This problem may be a contributing factor in the discrepancies seen in eye morphology described by the authors above.

Concerning male body size in this species, it is interesting to note that this is the only species in the A. abyssorum complex where males can reach or exceed female body length; in the other species terminal males are always much smaller than females (Andres 1983; Duffy et al. 2013). Our material examined also confirm this anomaly in size difference. Possible reasons for this size discrepancy will require future investigation.

The Southern Ocean endemic A. scotianensis can be easily distinguished from the three other species of the A. abyssorum complex by the following combination of characters: the absence of small dorsal humps on pereonites 1–7 and pleonites 1–2; the short uropod 3 inner ramus, which just reaches (or very slightly exceeds) the distal end of article 1 of uropod 3 outer ramus; the epistome usually slightly protruding in front of the upper lip; the maxilla 1 palp, with distal margin strongly convex and distal spines not-contiguous and by the nearly straight (female) distal margin of maxilliped inner plate. Further, A. scotianensis is also distinguished from A. shannonae sp. nov. and A. patriciae sp. nov. by the absence of an excavated palm in the gnathopod 2 propodus of mature females.