The order
Notostraca comprises the single family
Triopsidae, containing the
tadpole shrimp or
shield shrimp. The two genera,
Triops and
Lepidurus, are considered
living fossils, having not changed significantly in outward form since the
Triassic. They have a broad, flat
carapace, which conceals the head and bears a single pair of compound eyes. The abdomen is long, appears to be segmented and bears numerous pairs of flattened legs. The
telson is flanked by a pair of long, thin caudal rami.
Phenotypic plasticity within taxa makes species-level identification difficult, and is further compounded by variation in the mode of reproduction. Notostracans are
omnivores living on the bottom of
temporary pools and shallow lakes.
