Thorn isopod

Ancinus depressus

Family AncinidaeĀ  - marine isopods

Small, oval, depressed, twice as long as wide; color white or cream; body with a hard calcified exoskeleton; head short, rounded lateral edges, 2 eyespots; 2 pair segmented antennae; thorax (upper body) segmented crosswise, lateral sides angled downward; abdomen (lower part) with 2 segments, 1st mostly or entirely hidden under last thorax segment, terminal segment triangular, truncate at point, curled inward on underside; legs on underside segmented, fold inward, 1st pair of legs subchelate, i.e. 2nd to last segment a circular disk; last segment is a half claw folding in on circular disc; 2nd pair of legs unbranched on tips, rest of legs branched on terminal segment; uropods (the extensions on the last abdominal segment) unsegmented, unbranched, long and tapering.
Similar Species
The thorn isopod can be distinguished by its downward angled laterals on the segments and by its long, unbranched, tapering uropods.
Gulf, intertidal zone and shallow sandy waters, buries in the sand
Maximum Size
1.2 cm (1/2 in)
Other Common Names
flat pill bug
Previous Scientific Names
May look like a terrestrial pill bug. The thorn isopod can roll itself into a ball and lock its head into the grooves on the underside of the abdomen. Special thanks to Ashley Wiseman, TAMUG student, for collecting the critter.