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Characteristics, distribution and ecology
Taxonomische classification
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Gooday, 1981

Diagnosis
Carapace outline resembles many other species in the rotundata group. In lateral view carapace tapers only slightly anteriorly (C. obtusa Habitus 1, C. obtusa Habitus 3). Ventral outline not strongly biconvex, in male breadth >41% of length. Antero-ventral edge of each valve below the incisure blunt in lateral view (C. obtusa Habitus 2, C. obtusa Habitus 4). The left asymmetrical gland <12% of length behind tip of rostrum. Male first antenna "e" seta armature 12-14 pairs of spines (C. obtusa 4).

Remarks
C. obtusa is similar to C. fowleri (Conchoecia fowleri) but is smaller, less tapered so it appears more rectangular. The posterior margin is more symmetrically rounded, the males are relatively broader and the left asymmetrical gland opens more anteriorly than in C. discoveryi (Conchoecia discoveryi).

Distribution
Particularly common at mid-latitudes in the more oligotrophic regions 30°-40°N, far less abundant both polewards and equatorwards. Its overall bathymetric range is 100-800m, but it is most abundant at 400-700m. North Atlantic most common 30°-40°N, rarer to the north and to the south. Possibly also occurs in Indian and Pacific Oceans. 1, 2, 3 (R.R.S. Discovery Map).

Type specimens
Holotype, a dissected male British Museum (Natural History) No 1979.700. Paratypes, a dissected female 1979. 701, and 41 females and 42 males No 1979.726-735.

Type locality
Discovery Station 7856 haul 2, 29°53.67'N, 23°09'W, Depth 405-505m, 31st March 1972, 0911-1110h, gear RMT 1.

Conchoecia obtusa