Sars, 1866
Diagnosis
Marked sexual dimorphism in carapace shape and size (C. obtusata Habitus 1, C. obtusata Habitus 3). In both sexes, the dorsal margin nearly straight with postero-dorsal corner forming angle of about 45°. Posterior margin strongly arched curving continuously into the ventral margin. In lateral aspect, the male carapace tapers posteriorly. In female, maximum breadth just posterior to mid-length (C. obtusata Habitus 2). Left asymmetrical gland opens just behind posterior end of the hinge, right asymmetrical gland opening almost directly below the left on the tapering margin. Sculpturing in a few specimens in the form of weak concentric striations.
Female, frontal organ straight, undifferentiated, ending in a sharp point, with a few spines on the ventral surface near the end (C. obtusata 1). First antenna segmentation obscure, a long hirsute dorsal seta extending almost to the end of the capitulum, "e" seta with a sparse fringe of long hairs along its anterior edge; it is just over twice the lengths of the sensory setae. Second antenna endopodite, "a" and "b" setae with short hairs (C. obtusata 2), the "h", "i" and "i" setae are only slightly shorter than the "f" and "g" setae.
Male, frontal organ stem similar in length to first antenna, capitulum down-turned, hirsute on basal half, with rounded end (C. obtusata 3). First antenna "a" seta convoluted but similar in length to "c" seta and the second podomere, "b" and "d" setae sub-equal, little shorter than "e" seta, armature of "b" seta about seven pairs of very fine pointed spines giving way basally to a further 17 or so alternating spines (C. obtusata 4). Second antenna right-hand endopodite with spinose "b" seta and relatively large hook appendage bent through two angles (C. obtusata 5). The left-hand hook appendage reduced to a single straight shank. Copulatory appendage, large relative to most other Conchoecia species, has 8-13 transverse muscles.
Remarks
This is a high latitude species which has a Southern Ocean counterpart, C. antarctica. Initially, the earlier authors (e.g. Müller, 1906) considered it to be most closely related to C. parthenoda (Conchoecia parthenoda), but the two species have little in common other than a superficial similarity in carapace shape. Martens, 1979 erected the genus Obtusoecia to accommodate the two species, considering they did not fit with the other species Poulsen included in his genus Spinoecia.
Distribution
High latitude (>40°N) Northern Hemisphere endemic species. Its bathymetric range is shallow mesopelagic. 1, 2, 3, 4 (R.R.S. Discovery Map).
Type specimens
None designated; status of original material unknown.
Type locality
Lofoten Islands, Norway.