Marine Species Identification Portal : Discoconchoecia elegans

(Sars, 1866)

Description
Male carapace length longer than female. Carapace tapers anteriorly and shoulder vaults are well developed in both sexes [C.elegans-fem-lat; C.elegans-male-lat]. 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].

Size
Female 1.0-2.0 mm, male 1.0-2.1 mm carapace length.

Depth range
Shallow to deep mesopelagic.

Distribution in the North Sea
Northern North Sea, Skagerrak, Kattegat (Klie, 1944b).

World distribution
Recorded from all oceans, 80°N - 55°S in Atlantic.

Remarks
According to recent taxonomic revision, the species elegans is placed in the genus Discoconchoecia (M.V. Angel, pers. com.). However, for technical reasons, the former generic name Conchoecia had to be remained in the multimedia files.
In the North Atlantic D. elegans is abundant at mesopelagic depths, and is common in fjords; Brady and Norman (1896) recorded it in abundance in Loch Etive near Oban in W Scotland. Its variations in length are far broader than in any other species. Originally described as being 2 mm in length, subtropical specimens are only 1 mm long. Off southwest Ireland the mean size of females is around 1.6 mm but large samples show the population ranges in size from 1.1-1.9 mm. 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.

[After Angel, 2000]

Discoconchoecia elegans