New deep-sea Atlantic and Antarctic species of Abyssorchomene De Broyer, 1984 (Amphipoda, Lysianassoidea, Uristidae) with a redescription of A. abyssorum (Stebbing, 1888)

Abstract. During the Census of Marine Life Polarstern ANDEEP I-III and Meteor M79/1 DIVA3 expeditions, autonomous baited trap systems were employed to sample the mobile, necrophagous amphipods from abyssal depths. Within DIVA-3 (July 10–August 26 2009), a free-fall baited trap was used successfully at three stations in the southwest Atlantic, once in the Argentine Basin and twice in the Brazilian Basin. A total of twenty-one stations were sampled by baited traps during the ANDEEP I-III (2002, 2005) cruises in the Southern Ocean. Trap sets recovered large numbers of scavenging lysianassoid and alicelloid amphipods, including specimens of the widespread and commonly considered cosmopolitan uristid species Abyssorchomene abyssorum (Stebbing, 1888). During examinations of these and other North Atlantic collections of A. abyssorum, two similar new species A. patriciae sp. nov. and A. shannonae sp. nov. were discovered. Important morphological characters which differentiate the two new species from their congeners are found in the shape of the head lobe, coxa 1, gnathopod 2, coxa 5, pereopod 7 basis and uropod 3 rami length. The new species are fully figured and an identification key is provided. Abyssorchomene abyssorum is redescribed and for the first time, the female is fully described and illustrated from new material. The Southern Ocean endemic A. scotianensis (Andres, 1983) is also described and illustrated from new collections to complement the original description.

Type specimens and voucher material of Abyssorchomene abyssorum, A. patriciae sp. nov., A. scotianensis and A. shannonae sp. nov. are deposited at the following natural history institutions: Royal Belgian Institute of Natural Sciences (RBINS), Brussels (Belgium); Canadian Museum of Nature (CMN), Ottawa (Canada); Natural History Museum (NHM), London (UK) and the Zoological Museum, Hamburg (ZMH).
The following abbreviations are used in the fi gures:

New diagnosis
Pereonites 1-7 and pleonites 1-2 with a weak but distinct dorsoposterior hump on each segment. Lateral cephalic lobe broadly rounded, dorsal margin regularly convex and slightly more convex than the nearly straight ventral margin. Antennae 1-2 of male with calceoli, female without. Epistome level with upper lip. Maxilla 1 palp, distal end weakly convex with conical apical spines contiguous. Maxilliped inner plate, distal margin conspicuously excavate; outer plate inner margin not scalloped. Coxa 1 slightly widened distally, ~ 1.2-1.3 × proximal width. Gnathopod 2 propodus of male and female narrow, length ~ 2.3-2.5 × width, dactylus very small, inserted on the posterodistal one-third of distal margin, palm lacking concavity. Coxa 5 very weakly posterolobate, posterodistal lobe narrow with posterodistal margin nearly straight. Pereopod 7 basis with anterior margin slightly concave, posterior margin subparallel to anterior margin in the proximal two-thirds, distal third with a distinct, nearly straight bevel (male less distinct and more rounded). Uropod 1 peduncle length greater than 1.5-1.7 × length of outer ramus. Uropod 3 inner ramus extends past distal end of article 1 and reaches ~ 70% length of article 2 of outer ramus. Telson cleft ~ 52-56% of length.
UROSOMITE 1 (Fig. 2). With a deep, narrow dorsal concavity in front of the strong, regularly rounded dorsal boss, convex on posterior margin, boss projecting strongly upright and backward, slightly overhanging urosomite 2.
MANDIBLE. Incisor distinctly convex and slightly widened, dorsolateral and ventromedial corners with small tooth; left lacinia mobilis slender, curved, distally with small teeth, right lacking; accessory spine row with 3 strong spines, interspersed with fi ne setae; molar somewhat falciform, not columnar, forming a narrow crest, acutely produced on proximal end, setose with small triturative surface, hairy process (cf. Oleröd 1975) located proximal to molar; palp attached proximal to molar; article 2 with 15A2 setae, article 3 missing (refer to Fig. 6 of male holotype for general morphology and setae details). LOWER LIP. Outer lobes broad, inner margins strongly setose, distal inner margins excavated; without inner lobes; mandibular processes rounded.
MAXILLA 1 (Fig. 2). Outer plate with 11 spine-teeth in 7/4 crown arrangement; palp article 2 widened, with 9 contiguous (or nearly contiguous, separated by much less than the width of a spine) distal conical spines and one apical strong seta on outer corner; inner plate short with subrounded apical projection, and two unequally sized plumose setae inserted subapically (refer to Fig. 7 of male holotype for general morphology).
MAXILLA 2. Outer and inner plates strongly tapering distally, both lined with strong rows of pectinate medial marginal spines and setae; inner plate much shorter and slightly narrower than outer plate, apex just reaching the proximal end of medial setal row of outer plate (refer to Fig. 7 of male holotype for general morphology). MAXILLIPED (Fig. 2). Inner plate short, reaching about one third length of outer plate and reaching half length of palp article 1; outer corner of inner plate reaching about the level of the basal insertion of palp article 2; inner plate, distal margin conspicuously excavate, with slight mediodistal extension protruding slightly higher than the outer corner, with 3 weakly protruding nodular spines, unequally spaced, the two inner nodular spines closer to each other, the third nodular spine at the bottom of the excavation; outer plate well developed, subovate, length 1.8 × width, distal margin of outer plate reaching slightly below the distal margin of palp article 2, with two dissimilar apical spines and numerous (~ 12) strongly  (Stebbing, 1888), holotype, ♂, 7.5 mm (BMNH 1889.5.15.23). Scale bar = 0.1 mm. embedded, medial nodular spines, medial margin nearly smooth; palp strongly setose medially, article 4 well developed, about 60% of the length of article 3, with few apical fi ne setae on inner margin (refer to Fig. 7 of male holotype for general morphology).
GNATHOPOD 1 (Fig. 3). Coxa moderately widened, distal width 1.3 × proximal width and about 72% of length; anterior margin weakly concave; posterior margin very slightly concave, nearly straight; distal margin slightly convex in posterior half, more strongly convex in anterior half; basis stout, as wide as propodus, anterior margin with 7 very short setae; ischium subequal to merus; carpus short, less than half the length of propodus, posterodistal lobe not guarding propodus; propodus subchelate, subrectangular, very weakly tapering, length 1.57 × width, posterior margin slightly concave with distinct infl exion point at about distal two-thirds; palm slightly convex, with irregular microserrations, palm corner with 2 blunt protrusions and defi ned by 1 medial and 1 lateral spine; dactylus barely overriding palm corner.
Similar to female, but differing as follows: BODY. Smaller than female and slightly less robust. LATERAL HEAD LOBE (Fig. 2). Slightly narrower.
MAXILLA 2 (Fig. 7). Outer and inner plates strongly tapering distally, both with strong rows of pectinate medial marginal spines and setae; inner plate much shorter and narrower than outer plate (narrower than female), apex just reaching the proximal end of medial setal row of outer plate. MAXILLIPED (Fig. 7). Inner plate short, reaching about 0.3 × length of outer plate and reaching half length of palp article 1; outer corner of inner plate reaching about the level of the basal insertion of palp article 2; inner plate, distal margin conspicuously excavate, slight mediodistal extension about equal to outer corner (lower than female), with 3 weakly protruding nodular spines, unequally spaced, the two inner nodular spines closer to each other, the third nodular spine at the bottom of the excavation; outer plate well developed, subovate, length 1.8 × width, distal margin of outer plate slightly shorter than distal margin of palp article 2, with two dissimilar apical spines and numerous (9-10) strongly embedded, medial nodular spines, medial margin nearly smooth; palp strongly setose medially, article 4 well developed, about 60% of the length of article 3, with 3 apical setae on inner margin (note: medial marginal setae omitted on palp of Mxpd).

Remarks
Orchomene abyssorum was described by Stebbing (1888), from a single male specimen (about 7.5 mm long) collected by the HMS Challenger in the Argentine Basin at a depth of 3475 m. As shown by the extensive citation list, Abyssorchomene abyssorum has been widely reported and is generally considered as having a wide-ranging, even cosmopolitan distribution (Barnard & Ingram 1990;Thurston 1990Thurston , 2001Barnard & Karaman 1991;Duffy et al. 2013), but this concept is being challenged and will change with our study. There are still many questions regarding species identity of single specimens which await confi rmation by critical study of the material.
We examined and refi gured the male holotype specimen (appendages and mouthparts; the carcass is apparently lost). As a result, we have noticed some obvious discrepancies between our observations and drawings, and the original illustrations of Stebbing. Some of these are as follows (Stebbing's differences are outlined in parentheses): antenna 1 peduncular article 1 dorsal margin is less convex and the ventral margin is less concave (vs dorsal margin strongly convex, ventral margin strongly concave); mandible palp article 3 is straighter (vs strongly curved and more falciform); maxilla 1 palp is shorter, less curved with the distal margin straighter (vs palp longer, more strongly curved with distal margin strongly convex); maxilla 2 outer plate broader (1.35 ×), (vs very narrowed, much less than width of inner plate); maxilliped outer plate shorter, with inner margin nearly straight (vs outer plate longer, with inner margin concave and strongly serrated); gnathopod 1 propodus is broader (length 1.5 × width) with a short carpal lobe (vs longer, length 2 × width and more curved, with a longer carpal lobe, strongly guarding the hind margin); gnathopod 2 propodus has a very slight concave ventral margin, with a small dactylus and the posterodistal margin is slightly convex (vs strongly concave ventral margin, with a larger dactylus and the posterodistal margin is strongly sloped, level with the dactylus); epimeron 3 is narrowly rounded at the posteroventral corner (vs more broadly rounded at the posteroventral corner) and the dorsal boss of urosomite 1 is narrowly rounded and more upright (vs broadly rounded and lower). There are other minor differences which we have not included here. Reasons for these discrepancies are most likely numerous but possibly related to microscopy drawing technique and available equipment, attention to various details and whether these were completed freehand in some cases.
A special dimorphic character has been found in the male uropod 2 outer ramus distolateral spines. They are in a comb-like arrangement and are much stouter and bluntly rounded, more numerous and more closely spaced distally, with the proximal spine(s) being acute. This morphology and arrangement of ramal spines are not found in females, which are always acute, slender and more evenly spaced. The function of this peculiar spine morphology and arrangement in males are unknown, but possibly related to mating. All male specimens of Abyssorchomene discussed present this uropod 2 outer ramus spine character and it has not been reported or elaborated in the literature as far as we know (see Figs 2,9,17,25,33).
Part of the material identifi ed by Chevreux (1903) from the Hirondelle campaign 1896 (station 730 near the Azores, depth 2660 m) was also examined. It consisted of nine female specimens including fully mature ones. These specimens present all the diagnostic characters of Abyssorchomene abyssorum as redescribed here (in particular, the weak dorsal corrugations -sometimes diffi cult to distinguish -and the narrow female gnathopod 2 propod without an excavate palm), confi rming Chevreux's identifi cation. The rest of Chevreux's material (1935) collected from some other North Atlantic abyssal regions has not been seen and remains to be carefully checked. Walker (1903) recorded three specimens of which one is registered in the Natural History Museum (London) collections: BMNH 1905.9.7.23: one specimen, 6 mm, non-gravid, without visible oostegites, male (?), with gnathopod 2 propod length more than twice the width and palm straight, without a proximal concavity (Lauren Hughes, pers. com.), which does not allow to differentiate it from the male of A. patriciae sp. nov. In his paper, Walker did specifi cally thank Stebbing for verifi cation of his Orchomene abyssorum identifi cation, but we consider this identifi cation as uncertain.
We also checked the single specimen identifi ed by Stephensen (1925) from the Ingolf 1895-96, station 91, North Atlantic, west of Iceland, 64°44′ N, 31°00′ W, depth 2317 m, bottom 3.1°C, held in the Zoological Museum, University of Copenhagen (ZMUC). The specimen is fragmentary and in poor condition, with the head missing. We recognise it as a male. The slender gnathopod 2 propodus was used by Stephensen to attribute the specimen to Orchomenopsis abyssorum, but this male character is shared by all species of the A. abyssorum complex. So, due to the poor and incomplete condition of this specimen, the defi nitive identifi cation remains unclear. Dahl (1959) discussed a 12 mm female specimen from the Galathea station 649, southwest Pacifi c, Kermadec Trench, 35°16′ S, 178°40′ W, depth 8210-8300 m, grey clay with pumice, 14 February 1952, also held in the ZMUC collections, but unfortunately provided no fi gures. We examined his material and found that it differs from A. abyssorum by the more strongly expanded coxa 1, the proportionally shorter propodus of gnathopod 1, the wider, subovate propodus of gnathopod 2 and the strongly convex distal margin of maxilla 1 palp. As well, this material comes from much greater depths than A. abyssorum. We conclude that it is possibly a new species of Abyssorchomene.
From the fi gures and comments provided by Birstein & Vinogradov (1960), including the fi rst detailed reference to a female (from the Kermadec Trench), we are of the opinion that their specimens differ in many characters from A. abyssorum as redescribed here. We have not seen this material. The fi gures show that these specimens differ in the following ways: in the more elongate carpal lobe of gnathopod 1 slightly but distinctly guarding the propodus, the proportionally smaller and narrower male gnathopod 1 propodus, the more elongate carpus of gnathopod 2, the distinctly curved propodus of gnathopod 2, the slightly spaced terminal spines on the maxilla 1 palp, the slightly different shape of the pereopod 7 basis with the hind margin parallel to the anterior margin on two-thirds of its length, the shorter inner ramus of uropod 3 and the sinuous inner margins of the telson lobes. Contrary to Barnard & Ingram (1990), we doubt that these morphological differences in the Kermadec Trench specimens can be considered as intraspecifi c variations of A. abyssorum. Until these specimens are examined in detail, the species attribution remains unknown. Birstein & Vinogradov (1964) collected, in the Central Indian Ocean, a male (8 mm) that we cannot attribute with certainty to A. abyssorum, as there were no illustrations of the specimen and we were not able to examine the material to confi rm its identity. Barnard & Ingram (1990) redescribed in detail A. abyssorum based on new material (a single small male, 6.41 mm, Scripps Institution of Oceanography (SIO), station 882, Galapagos Vents area, 00°47.9′ N, 86°09.2′ W, depth 2491 m). They considered Chevreux's (1900Chevreux's ( , 1903Chevreux's ( , 1935 North Atlantic material, as well as Birstein & Vinogradov's (1960) records as the only fi rm identifi cations of A. abyssorum. The small male described and fi nely illustrated shows the gnathopod 1 carpal lobe slightly more elongate and guarding the propodus to a greater degree than on the type and DIVA-3 specimens. The pereopod European Journal of Taxonomy 825: 1-76 (2022) 26 5 basis has a slightly different relative length: it is shorter than the coxa instead of longer in the type specimen and the DIVA-3 males. This shape is closer to that of the DIVA-3 female described here and may be due to the immature state of the specimen. The epimeron 3 shows a slightly sinuous posterior margin which is very slightly and regularly convex, but nearly straight in the type, DIVA-3 and Chevreux's material. Like Stebbing (1888), Barnard & Ingram (1990) did not mention the presence of the weak dorsal corrugations, clearly distinct on our DIVA-3 material and slightly less so in Stebbing's fi gure of pleonites 1-2, but not on the pereonites on his in-toto illustration. Other minor differences between the male described by Barnard & Ingram (1990) and the type and DIVA-3 male specimens include: the shorter extension of the poorly distinct eye, i.e., 44% of the head height instead of 75% (a character however unclear and somewhat unreliable in long preserved specimens); the much narrower lateral head lobe; the coxa 4, with a very different shape and smaller posteroventral lobe; the coxa 5 width subequal to its height (instead of slightly wider than high); the much shorter inner ramus of uropod 3; the maxilla 2 with tip of inner plate not reaching the basal end of outer plate setal row and the nodulous apical spines of the maxilliped inner plate located differently. Given all these differing characters, it is unlikely to belong to A. abyssorum and at this time the specifi c attribution of this single male specimen remains unresolved. Thurston (1990) collected A. abyssorum in four North Atlantic abyssal plains by bottom traps or midwater trawls but didn't make any morphological comment. It is important to note that not all the specimens in this paper were seen by Thurston (Tammy Horton, pers. com.). However, T. Horton (pers. com.) checked the sample from the Porcupine Abyssal Plain (see Table 1) and concluded it belongs to A. patriciae sp. nov. This likely applies to all the samples examined by Thurston 1990.
Concerning the Southern Ocean material attributed to A. abyssorum (Schellenberg 1926;Barnard 1932;Nicholls 1938;Dahl 1954), Dahl (1959) expressed his doubts about its conspecifi ty with A. abyssorum (Stebbing 1888). Andres (1983) defi nitively distinguished the Antarctic continental shelf specimens from the abyssal and hadal ones in describing A. scotianensis. He considered the juvenile specimens of Schellenberg (1926) as belonging to his new species but couldn't confi rm the affi liation of the specimens of Barnard (1932), Nicholls (1938) and Dahl (1954), as the length-width relationship of coxa 1 and of the basis-propodus of gnathopod 1 were not described.
All A. abyssorum identifi cations should be carefully checked by considering the new species described here. In Table 1, we tentatively attribute the various records to the most likely correct species determined by our study.
Abyssorchomene abyssorum shares with the two new species, A. patriciae sp. nov. and A. shannonae sp. nov. dorsodistal corrugations on the pereonites 1-7 and pleonites 1-2, a character unique among all the species of the genus Abyssorchomene (sensu Lowry & Kilgallen 2014;Horton et al. 2021). This character separates this complex from the remaining Abyssorchomene species. All three species are very close morphologically and males are very diffi cult to separate.
In A. abyssorum, the gnathopod 2 propod, similar in both sexes, is very slender (length 2.3-2.5 × width) and the palm presents a very narrow gap and lacks a concavity. In contrast, the females of A. patriciae sp. nov. and A. shannonae sp. nov. have a broadened, suboval propod (length 1.5-1.7 × width) with a very distinct concavity on the palm. Coxa 1 is slightly (females) to weakly (males) widened distally. It is slightly more widened in both the new species, A. patriciae and A. shannonae (especially in females). Coxa 5 is very weakly posterolobate in A. abyssorum but distinctly more in A. patriciae and A. shannonae. The distal bevel of the posterior margin of the pereopod 7 basis is straighter in A. patriciae and A. shannonae, and in the former species, the basis is more subrectangular, with the front margin straight. The uropod 3 inner ramus extends to about 70% of the length of the outer ramus article 2; in A. shannonae, it is much shorter, reaching about 20-25% of the length of the outer ramus article 2 and in A. patriciae, the inner ramus reaches to about 63% of the length of article 2. Other differences are provided in the key to the species (see p. 68).
Lateral cephalic lobe broadly rounded, dorsal and ventral margins slightly dissimilar in shape, dorsal margin strongly convex, ventral margin nearly straight with a very slight concavity. Antennae 1-2 of male with calceoli, female without. Epistome level with and scarcely differentiated from upper lip. Maxilla 1 palp distal end weakly convex and with conical apical spines contiguous. Maxilliped inner plate, distal margin shallowly but distinctly concave, with a very weak mediodistal extension; outer plate inner margin very weakly scalloped. Coxa 1 distinctly widened, distal width 1.3 × proximal width or greater. Gnathopod 2 propodus of female broadened, subovate, length 1.7 × width (different in form to narrow male propodus), dactylus large, inserted at the top of distal margin and occupying most of the length (~ 85%) of the distal margin, forming a distinct, small gap on the palm. Coxa 5 posteroventral lobe narrowly rounded, posterior margin with distinct straight section. Pereopod 7 basis, posteroventral corner shallowly and weakly beveled. Uropod 1 peduncle relatively short, length less than 1.5 × length of outer ramus. Uropod 3 inner ramus extends to ~ 63% of article 2 of uropod 3 outer ramus. Telson cleft ~ 52% of length.

Etymology
The species name is dedicated to Patricia De Broyer, the daughter of the co-author.
UROSOMITE 1 (Fig. 11). With a deep, narrow dorsal concavity in front of the strongly projecting, slightly unequally rounded, dorsal boss, slightly overhanging urosomite 2. HEAD (Fig. 11). Slightly longer (1.13 ×) than pereonite 1. LATERAL CEPHALIC LOBE (Fig. 11). Broadly rounded, dorsal and ventral margin not similar in shape, dorsal margin strongly convex, ventral margin nearly straight with a slight concavity. EYE (Fig. 11). Non ommatidial, formed of pigment granules; long, narrow, L-shaped, extending parallel to the front head margin, length about 63% of the head height (note: eye shape and size are best observed with fresh specimens, as over time in preservation the labile components of the eye pigments can be lost, causing the eyes to become extremely diffi cult to ascertain-see eye of freshly collected male, Fig. 10).
MAXILLA 2 (Fig. 13). Outer and inner plates tapering distally, both with strong rows of pectinate medial marginal spines and setae; inner plate much shorter and distinctly narrower than outer plate, with marginal setae on the distal third of the inner margin, distal end of inner plate not reaching the proximal end of setal row of outer plate. MAXILLIPED (Fig. 13). Inner plate subrectangular, extending slightly past the distal end of the inner margin of palp article 1 and reaching about 0.34 × length of outer plate, distal margin shallowly but distinctly concave, with very weak mediodistal extension, not surpassing the level of the weak outer extension, with 3 strongly embedded nodular spines, the two mediodistal marginal nodular spines situated close to each other, the third one located in about the middle of the plate, medial margin strongly setose; outer plate elongated, subovate, length 1.83 × width, reaching the distal end of palp article 2, with two dissimilar apical spines and numerous (12) embedded, medial nodular spines, medial margin very slightly scalloped; palp strongly setose medially, article 4 well developed, about 0.56 × length of article 3, inner margin with 2-3 distal setae.
GNATHOPOD 1 (Fig. 14). Coxa distinctly widened, distal width 1.3 × proximal width and about 76% of length, anterior margin concave, anterodorsal corner rounded, posterior margin nearly straight, distal margin strongly convex in anterior half, weakly convex in posterior half, posteroventral corner not narrowly rounded; basis stout, width about one third of the length and similar to propod width, anterior margin with very short setae; ischium subequal to merus, both with posterior margins setose; carpus short, about half the length of the propodus, with produced narrow posterodistal lobe, not guarding the hind margin of propodus; propodus subchelate, subrectangular, slightly narrowing distally, with anterior margin regularly convex, posterior margin slightly concave, with a distinct infl exion at distal two-thirds, palm transverse, microcrenulate, palmar corner with 2 blunt protrusions and defi ned by 1 medial and 1 lateral spine; dactylus subequal to palm or barely overriding palm corner.
UROPOD 3 (Fig. 17). Peduncle 0.77 × length of biarticulate outer ramus; second article of outer ramus 0.38 × length of article 1; inner ramus extends past distal end of article 1 of outer ramus and reaches 0.63 × length of article 2 of outer ramus, inner margins of rami with long plumose setae and outer margins with a few slender spines. TELSON (Fig. 17). 1.7 × longer than wide, cleft (52%), lobes tapering distally with 2-3 lateral, submarginal spines and 1 distal spine set in middle of lobe tip.

Remarks
In many subtle ways, the new species Abyssorchomene patriciae sp. nov. appears to be a pseudocryptic species, with a facies very superfi cially similar to both the north and southwest Atlantic species A. abyssorum (Stebbing, 1888) and the southwest Atlantic-Antarctic new species A. shannonae sp. nov. (this paper). For instance, these three species all possess the slight, but distinct dorsoposterior rounded hump on pereonites 1-7 and pleonites 1-2, which is unique among Abyssorchomene. As well, the uropod 3 inner ramus extends past the distal end of article 1 of the outer ramus of uropod 3. These characters easily differentiate A. abyssorum, A. patriciae and A. shannonae from the Southern Ocean endemic A. scotianensis (Andres, 1983).
In general body shape and form, they are all extremely similar. However, upon critical examination, we have found several detailed morphological characters that differentiate A. patriciae sp. nov. as follows (character of A. abyssorum in brackets). From A. abyssorum, it differs in the shape of the lateral head lobe, with dorsal and ventral margins not similar, dorsal margin strongly convex, ventral margin nearly straight with slight concavity (vs dorsal and ventral margins more similar, dorsal margin weakly convex and ventral margin straighter); coxa 1 is distinctly widened distally and the anterodorsal corner is broadly rounded in the female (vs only very slightly widened and the anterodorsal corner is narrowly rounded in the female); the mature female gnathopod 2 propodus broadened, subovate, length ~ 1.7 × width, dactylus large, inserted at the top of the distal margin and occupying most of the distal margin, with a small palmar gap (vs propodus very slender, similar to male, length ~ 2.5 × width, dactylus tiny, without a palmar gap); the shorter uropod 1 peduncle, which is 1.45 × the length of the outer ramus (vs longer uropod 1 peduncle, which is 1.5-1.7 × the outer ramus) and the length of the uropod 3 inner ramus, which reaches to ~ 63% of article 2 of uropod 3 outer ramus (vs reaching to ~ 70% of article 2 of outer ramus). The broadened gnathopod 2 propodus of mature females is not found in smaller, immature females and is likely a terminal growth stage character which presents at maturity, when brood plates are fully formed with long brood setae. Immature females possess a gnathopod 2 propodus which approximates the condition found in males. These are slender and lack the palmar concavity. This makes these taxa diffi cult to separate without mature females; however, we give other characters which, in total, aid in identifying these species without mature females. Several of these small differences are found in the mouthparts, especially maxilla 2 and the maxilliped and these are outlined in the descriptive text for this species.
The characters that differentiate A. patriciae sp. nov. and A. shannonae sp. nov. are outlined in the Remarks section under A. shannonae (p. 67) and in the key (p. 68).

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. • 1 ♀ (9.5 mm, head fi gured); same collection data as for preceding; CMNC 2022-0006 • ♂ (12.4 mm, fi gured, 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.  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.

ROSS
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 defi ned 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 fi nely 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 fi tting palm, inner margin bearing distally a spiny protuberance fi tting to the palm and weakly denticulate projection.
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.
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).
TELSON. Slightly narrower and longer, length 1.75 × width; cleft slightly deeper, about 55-60% of its length. 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: fi g. 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: fi g. 12).

Remarks
As discussed by Andres (1983), the juvenile Antarctic specimens identifi ed as Orchomenopsis chilensis f. abyssorum by Schellenberg (1926) may be attributed to Abyssorchomene scotianensis. The peculiar shape of the maxilla 1 palp article 2 fi gured 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 confi rmed fi rst. 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 identifi ed. Indeed, specimens we examined showed the typical, large "L-shaped eyes", with larger males having larger eyes (see . 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 diffi cult 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 confi rm 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.  (2022) 62 UROSOMITE 1 (Fig. 26). With a deep, broadly rounded dorsal concavity in front of the strong, regularly rounded, dorsal boss, slightly overhanging urosomite 2.
LATERAL CEPHALIC LOBE (Fig. 26). Broadly rounded, dorsal and ventral margin nearly equally convex. EYE (Fig. 26). Non ommatidial, formed of pigment granules; long, relatively narrow, crescent shaped; extending parallel to the front head margin, length about two-thirds of the head height.
MAXILLA 2 (Fig. 28). Outer and inner plates strongly 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 half of the inner margin; apex of inner plate slightly surpassing the proximal end of setal row of outer plate. MAXILLIPED (Fig. 30). Inner plate short, subrectangular, just reaching the distal end of the inner margin of palp article 1 and reaching about 0.3 × length of outer plate, distal margin not excavate, very weakly concave on outer half and sloped, with weak medio-distal extension, with 3 equally spaced, strongly embedded nodular spines, medial margin strongly setose; outer plate well developed, subovate, length 1.58 × width, not reaching inner distal end of palp article 2, with two dissimilar apical spines and numerous (10-11) embedded, medial nodular spines, medial margin distinctly scalloped; palp strongly setose medially, article 4 well developed, about half the length of article 3, with 6 apically plumose setae on distal inner margin.
GNATHOPOD 1 (Fig. 31). Coxa distinctly widened, distal width 1.53 × proximal width and about 80% of length, anterior margin slightly concave, anterodorsal corner broadly rounded, posterior margin slightly sinuous, the distal half weakly concave, slightly convex in posterior half, posteroventral corner nearly right angled, narrowly rounded; basis stout, not expanded, width one-third of the length, slightly narrower than propod, anterior margin with long setae; ischium subequal to merus; carpus short, about half the length of the propodus, with produced narrow posterodistal lobe, not guarding the hind margin of propodus; propodus subchelate, subrectangular, with anterior margin regularly convex, posterior margin distinctly concave, with infl exion point at distal two-thirds, palm transverse, microcrenulate, palm corner with 2 blunt protrusions and defi ned by 1 medial and 1 lateral spine; dactylus subequal to palm or barely overriding palm corner.
UROPOD 1 (Fig. 33). Peduncle long, about 1.6 × length of outer ramus and 1.74 × length of inner ramus, dorsolateral and dorsomedial margins spinose; inner ramus slightly shorter than outer, margins of rami with slender spines except medial margin of outer ramus, which lacks spines. UROPOD 2 (Fig. 33). Peduncle about 1.2 × length of outer ramus, dorsolateral and dorsomedial margins with 4 and 3 spines respectively; inner ramus very slightly shorter than outer ramus; outer ramus with closely spaced slender spines on dorsolateral margin; inner ramus margins with slender spines.
Male (Allotype 7 mm, ZMH K-61210). Similar to female, but differing as follows: BODY. Smaller than female, and slightly less robust. LATERAL HEAD LOBE. Slightly narrower.

Discussion
One of our aims was to revise and clarify the status of the wide ranging, but poorly known uristid scavenging amphipod, Abyssorchomene abyssorum (Stebbing, 1888). The long overdue and clearly needed redescription was initiated by examining the male holotype specimen and providing new, detailed illustrations of both the male and female. Further, a comprehensive account of the female is provided, previously not described in detail. This was facilitated by recovering specimens in baited trap collections from the DIVA-3 (2009) campaign in the southwest Atlantic, very close to the type locality of A. abyssorum. During detailed examinations of these collections and other North Atlantic material, we have also discovered and described two new species in the complex, A. patriciae sp. nov. and A. shannonae sp. nov. A key to the species of the A. abyssorum complex is also presented.
This study also attempted to verify the numerous previous identifi cations of A. abyssorum in the literature by borrowing and examining the specimens when possible. An extensive list of published records of A. abyssorum sensu lato (see Table 1) is given, with the most likely identifi cation based on our study. These identifi cations will require confi rmation, as we have not been able to examine all listed specimens. Given the very similar morphologies of the new species described here, all A. abyssorum identifi cations not verifi ed in this paper remain to be carefully checked and assessed. It is apparent to us that the numerous reports of A. abyssorum may contain several undescribed, morphologically similar species, two of which are described herein. Material of A. abyssorum from the Pacifi c and Indian Oceans await critical analysis.
Recent material from ANDEEP expeditions gave us the opportunity to provide new illustrations and descriptions of the Southern Ocean endemic A. scotianensis (Andres, 1983) to complement the original description. As the species had not been fi gured since, these new illustrations provide more clarity to the species, especially regarding the morphology of females.
As an obvious next step, there is a need for a genetic confi rmation of our morphology-based hypotheses. Recent molecular studies (Havermans et al. 2010(Havermans et al. , 2011Havermans 2012;Corrigan et al. 2014;Ritchie et al. 2015) have drawn attention to some issues concerning the taxonomic status of several species of Abyssorchomene, originating from traditional morphology-based taxonomy. Havermans (2012: chapter 8) emphasized that an Abyssorchomene clade (comprising A. chevreuxi, A. scotianensis and A. sp. n. 1 = A. shannonae sp. nov.) formed a well-supported monophyletic unit. However, molecular analyses of other species of Abyssorchomene are currently too limited to allow delineating the genus phylogeny (see Havermans 2012: tables 9-10).
On the other hand, our results bring a new confi rmation that many so-called deep-sea 'cosmopolitan' species are in fact often composed of several cryptic or pseudocryptic species with more restricted distributions (e.g., Brandt et al. 2012;Havermans et al. 2013;Krapp-Schickel & De Broyer 2014;d'Udekem d'Acoz & Havermans 2015;Bribiesca-Contreras et al. 2021;Jażdżewska et al. 2021). This emphasizes the need to carefully revise the existing identifi cations of all species of Abyssorchomene (see Horton et al. 2021), as other potential species may still await critical recognition within the complex.