Deevey, 1978
Diagnosis
Carapace with height about 60% length. The ventral margin curves almost symmetrically both anteriorly and posteriorly, so maximum height at midlength (C. arcuata Habitus 1, C. arcuata Habitus 3). The left asymmetrical gland, as is typical for the rotundata group, opens on the rostrum just behind the anterior end of the hinge. The right asymmetrical gland opens immediately below the posterior end of the hinge at the postero-dorsal corner.
Female, frontal organ capitulum undifferentiated and rather bulbous terminally (C. arcuata 1).
Male, frontal organ capitulum finely spinous over its proximal two-thirds; dorsal margin straight, ventral margin only slightly sinuate (C. arcuata 3). First antenna "a" seta long, "c" seta short; the "e" seta carries a row of twelve pairs of spines which are more widely spaced in the centre of the row (C. arcuata 4). One of the sensory setae on the endopodite of the second antenna is bifid (C. arcuata 5).
Remarks
Species described from the Pacific sector of the Southern Ocean, but had already been found occurring at bathypelagic depths off Bermuda. Now known to be a frequent component of bathypelagic plankton communities throughout the Northeast Atlantic. It is readily distinguished from its siblings in the rotundata group by the near symmetry of its lateral aspect, and the bifid seta on the endopodite of the second antenna.
Distribution
Southern Ocean and in the Atlantic from 0°-60°N. It is frequent at depths > 1500m. 1,2,3 (R.R.S. Discovery Map).
Type specimens
Holotype, A male dissected and mounted on a slide deposited in the Smithsonian Institution (USNM 169064).
Type locality
56°55'S 135°00'W; Eltanin cruise 17, sample 942; date 27th. March 1965; depth 1000-2000m; gear Bébathypelagic plankton sampler.