clam shrimp

Short definition from Wiktionary

Noun

1. 1
   Any branchiopod crustacean of the suborders Cyclestherida, Laevicaudata, or Spinicaudata (of the disused superorder Conchostraca), covered by a bivalve shell and well adopted to live in temporary, shallow ponds, with many identified extinct and extant species used to date strata.