Sars, 1865
Diagnosis
Male carapace length longer than female. Carapace tapers anteriorly and shoulder vaults are well developed in both sexes (C. elegans Habitus 1, C. elegans Habitus 3). Posterodorsal corner, angle slightly greater than 90°, right valve carries a small spine (C. elegans 4). Carapace sculpturing absent. Right asymmetrical gland opens at the postero-ventral corner, the left at the postero-dorsal corner.
Female, frontal organ undifferentiated, straight, round-ended and 10-20% projects beyond the end Of first antenna (C. elegans 1). The first antenna with minute dorsal seta in some populations, "e" seta twice the length of the other sensory setae.
Male, frontal organ partially differentiated, almost straight, capitulum with a sparse patch of spinules on the central ventral surface (C. elegans 5, C. elegans 6). First antenna with convoluted "a" seta slightly longer than the second podomere, "c" seta short, "b" seta shorter than the "d" seta, "e" seta armature characteristic oval patch of hairs of the elegans group (C. elegans 7).
Remarks
One of the earliest species to be described. In the North Atlantic it is abundant at mesopelagic depths, and is common in fjords; Brady and Norman, 1896 recorded it in abundance in Loch Etive near Oban in Western Scotland. Its variations in length are far broader than in any other species. Originally described as being 2mm in length, subtropical specimens are only 1mm long. Off southwest Ireland the mean size of females is around 1.6mm but large samples show the population ranges in size from 1.1-1.9mm. Larger specimens tend to occur deeper than the smaller, but unlike all other swarms of sibling species the juvenile instars cannot be separated by size. The impression is that there is a hybrid swarm between the larger polar form and the smaller tropical form. At 44°N the size variation was unrelated to season.
Martens, 1979 erected the genus Discoconchoecia to include all species with the armature on the male "e" seta of the first antenna as an oval pad of hairs, removing them from Poulsen's genus of Paraconchoecia.
Distribution
Recorded from all oceans, 80°N - 55°S in Atlantic. Shallow to deep mesopelagic. 1, 2, 3, 4 (R.R.S. Discovery Map).
Type specimens
None designated; status of original material unknown.
Type locality
Christiana Fjord, Norway.