1. Although Crustaceans exhibit a great variety of forms, the basic Crustacean body consists of a number of segments, or somite s. These somites sometimes are fused to form rigid areas and sometimes are free, linked to each other by flexible areas that allow some movement.

2. The last somite of the pleon or abdomen of certain crustaceans and Arachnidans.

3. …often referred to as the Cephalothorax. A pair of appendages is attached to each somite

4. Choline esterase activity appears again in the basal layer of somites out of which the sclerotome-cells migrate.