A taxonomical review of the Gnathophausia (Crustacea, Lophogastrida), with new records from the northern mid-Atlantic ridge Author Meland, Kenneth Author Aas, Pål Øyvind text Zootaxa 2013 3664 2 199 225 journal article 10.11646/zootaxa.3664.2.5 998f53b0-f46c-4525-bc3a-f8a597c01979 1175-5326 220335 5306204C-0DBC-4EE1-A008-B1582FA80243 Gnathophausia elegans G.O. Sars, 1883 ( Fig. 7 )

Gnathophausia elegans G.O. Sars, 1883:7 –8.—W.M.	Tattersall	1939:228;—Fage	1941:	41–44.—Bacescu	1991:87–88.—
Casanova 1996a: 129.
Gnathophausia elegansi— G.O. Sars 1885: 42–43.

Diagnosis. Body slender. Carapace does not cover last thorax somite; rostrum elongate, equaling carapace in length, denticulate; posterodorsal spine extending past second abdominal somite; posterolateral margins rounded; dorsal keel present, continuous, extending onto rostrum and posterodorsal spine, upper lateral keels absent or closely flanking dorsal keel; lower lateral keels distinct, curves upwards towards posterior end and merges into marginal keel beneath base of posterodorsal spine; supra-orbital spines well developed; branchiostegal expansions evenly rounded; antennal spines small. Outer spine of antennal scale extending past terminal lobe. Abdominal somites slender, dorsal spines absent, ventral margin of pleura drawn out into posterior projected spine. Telson as long as uropods; linguiform, distal two-thirds of lateral margins armed with spiniform setae; apex heart-shaped armed with two pairs of large spiniform setae, posterior margin fringed with serrated edge. Obtains lengths up to 56 mm (G.O. Sars 1885; Bacescu 1991). FIGURE 7. Gnathophausia elegans G.O. Sars, 1883 . Adult female. A, lateral view; B, dorsal view; C, antenna; D, telson (dorsal view); E, apex of telson (from G.O. Sars 1885: pl. VI, figs. 1–5). Distribution. G. elegans is only known from West Pacific waters. It has been collected as far north as Japan (W.M. Tattersall 1939), in Indonesia (Casanova 1996a), the Philippines (Bacescu 1991; W.M. Tattersall 1939), and as far south as the Fiji islands (G.O. Sars 1883) and New Caledonia (Casanova 1993). G. elegans has been collected at depths ranging from 267 to 4161 m . Remarks. G. elegans belongs to a morphogroup of Gnathophausia that do not have their dorsal keel interrupted by the cervical sulcus ( Fig. 7 A). Coupled with conspicuous lower lateral keels that extend post-dorsally and merge into the marginal keels ( Fig. 7 A), G. elegans is quite distinct from other Gnathophausia , but bears some resemblance to G. fagei (see discussion in “Remarks” of G. fagei ). Gnathophausia fagei Casanova, 1996 ( Fig. 8 ) Gnathophausia elegans fagei —Bacescu 1991: 88. Gnathophausia fagei Casanova, 1996a: 129 –130. Diagnosis. Body slender. Carapace does not cover last thorax somite; rostrum elongate, posterodorsal spine present; posterolateral margins rounded; dorsal keel present, continuous, extending onto rostrum and posterodorsal spine, upper lateral keels absent; lower lateral keels distinct, curve upwards towards base of posterodorsal spine, terminates abruptly, does not merge into the marginal keels; supra-orbital spines well developed; branchiostegal expansions evenly rounded; antennal spines small. Outer spine of antennal scale extending past the terminal lobe. Abdominal somites slender, dorsal spines absent, ventral margin of pleura on somites one to five drawn out into a posterior projected spine; spine positioned medially on first pseudo-somite of pleura six. Telson as long as uropods; linguiform, distal two-thirds of lateral margins armed with spiniform setae; apex heart shaped armed with two pairs of large spiniform setae, posterior margin fringed with a serrated edge. Obtains lengths up to 50 mm (Casanova 1996a; Bacescu 1991). FIGURE 8. Gnathophausia fagei Casanova, 1996 . A, carapace, lateral view; B, abdominal somite six; C, telson. Distribution. G. f a g e i has only bee reported on a few occasions from the type locality in the Makassar Strait, and from 500–1000 m trenches south of Lubang Island, South China Sea. Remarks. G. f a g e i was first established as a subspecies of G. elegans by Bacescu (1991) for two females and one juvenile specimen obtained from Indonesia at a depth of 1000 m . Subspecies status was diagnosed based on the lower later keels of these specimens not merging into the marginal keels as seen in G. elegans . Similar abruption of lateral keels is also seen in G. childressi and G.affinis , but both G. f a g e i and G. elegans can be distinguished from these two species by the dorsal keel being continuous and not interrupted by the cervical sulcus. Another distinguishing character for G. fagei is observed in the sixth abdominal pleura that are armed with medial ventral spines, opposed to a more posterior placement as observed in G. elegans ( Fig. 7 A). Considering overlap in distribution between G. elegans and G. fagei , coupled with only minor differences in morphology, which might possibly be due to morphogenetic variability between growth stages, only future records of additional specimens will help confirm species status of G. fagei .