What is "pygidium"

Pygidium \Py*gid"i*um\, n.; pl. Pygidia. [NL., fr. Gr. ?, dim. of ? the rump.] (Zo["o]l.) The caudal plate of trilobites, crustacean, and certain insects. See Illust. of Limulus and Trilobite.

n. (context zoology English) The caudal plate of trilobites, crustacean, and certain insect.

The pygidium (plural pygidia) is the posterior body part or shield of crustaceans and some other arthropods, such as insects and the extinct trilobites. It contains the anus and, in females, the ovipositor. It is composed of fused body segments, sometimes with a tail, and separated from thoracic segments by an articulation.