Rostrum, incisure, margins
Female conchoecia macrocheira
- Rostrum:
Anteriorly each valve is developed into a rostrum that overlies and protects the first antennae and frontal organ. The rostrum is produced into a long process in some species (e.g. Conchoecilla daphnoides), but reduced almost completely in others (e.g. Halocypris spp). - Incisure: Below the rostrum the incisure is through which the exopodites of the second antennae project laterally during swimming to provide the propulsive force.
- Margins:
- ventral margin of the carapace curves posteriorly and form either a rounded or abruptly angled corner with the posterior margin.
- In some species there are tubercles at the posterior ventral corner (genus Conchoecissa). Likewise the posterior margin may be more or less curved and can be armed with spines. It extends up to the posterior dorsal corner, which may be rounded or developed into spines on one of both valves of the carapace.
- The posterior half of the dorsal margin is more or less straight, but the anterior part is often arched forming the shoulder vaults that cover the large muscular protopodite of the second antenna. In a few species the shoulder vaults are sharp edged (B. antipoda and P. spinifera) or even winged (Alacia alata).
- ventral margin of the carapace curves posteriorly and form either a rounded or abruptly angled corner with the posterior margin.