Triops is a genus of small crustaceans in the order Notostraca (tadpole shrimp). Lepidurus is a genus of small crustaceans in the order Notostraca (tadpole shrimp). In roundworms, clam shrimp, tadpole shrimp and cancrid shrimps, androdioecy has evolved from dioecy. In some northern areas, tadpole shrimp are more common. The order Notostraca comprises the single family Triopsidae, containing the tadpole shrimp or shield shrimp.