This group of taxa has been the subject of considerable controversy and instability. The lysianassoid genera Orchomene, Orchomenella, Orchomenopsis, Allogaussia, Tryphosa are similar, but subsequent description of many intergradational species led Barnard (1964b) to regard all these genera as synonyms of Orchomene. Since then, some taxa have been judged invalid, some "old" orchomenoid species groups have been elevated to subgeneric or generic rank, new genera and subgenera have been described (Abyssorchomene, Orchomenyx), various species have been redistributed among old and new genera and subgenera, and the process continues to the present (see Barnard and Ingram, 1990; Barnard and Karaman, 1991; Lowry and Stoddart, 1994).
The following characters distinguish the group. All coxal plates large and high (Orchomenella abyssorum 1). Accessory flagellum of ANT I present, approximately 5-articulated (Orchomenella abyssorum 2; Orchomenella distinctus 1; Orchomenella gerulicorbis 1). Epistome blunt, produced anteriorly. Head with triangular lateral lobes. Mouth parts bundle not projecting conically below head. Mandibular molar weak, rounded, poorly but distinctly triturative; palp thin, attached proximal to molar. Palp of MX I 2-articulated, inner lobe with 2 strong apical setae. Lobes of MX II subequal, long, narrow (Orchomenella abyssorum 3; Orchomenella distinctus 4; Orchomenella gerulicorbis 4). Palp of MXP 4-articulated. Upper lip never projecting conspicuously in front of epistome. P I with small, clear subchela formed by dactyl and distal margin of rectangular ART 6 (Orchomenella abyssorum 6; Orchomenella distinctus 3; Orchomenella gerulicorbis 3). ART 2 of P III not deeply indented. Epimeral plate III with posterior margin serrate to smooth, or with concave posterior margin with large curved tooth on posteroventral corner. Urosomite I with dorsal carina (Orchomenella abyssorum 4; Orchomenella distinctus 2; Orchomenella gerulicorbis 2). Telson varying from triangular to rounded, from deeply cleft to entire.
About 90 species, mainly benthic or near-bottom scavengers. A few bentho-pelagic or pelagic species (e.g. O. pelagica, see Birstein and Vinogradov, 1960) have been reported from plankton samples as well as bottom traps (see Thurston, 1990 and Lowry, Stoddart, 1994). Only one such species was reported from the South Atlantic. Two others in northern tropical Atlantic waters may well cross the equator.
Orchomenella abyssorum (Stebbing, 1888)
Orchomenella distinctus Birstein and Vinogradov, 1960
Orchomenella gerulicorbis (Shulenberger and Barnard, 1976)
The generic status of the species treated here follows Lowry and Stoddart (1994). They belong to a group of about 14 similar species recognized as follows: lateral lobes of the head with rounded tops; ART 5 of P I with narrow posterodistal lobe; ART 5 of P II stout; ART 2 of P III ordinary, not proboscoid; posterior margin of epimeral plate III smooth, posteroventral corner rounded or at approximately 90°; dorsal carina of urosomite I hump-like, proboscoid, partly ovelapping urosomite II; rami of UR III setose (even weakly) in females, exopodite 2-articulated; Telson spinose, deeply cleft (see Shulenberger and Barnard, 1976).