A genus of CRUSTACEA of the order ANOSTRACA, found in briny pools and lakes and often cultured for fish food. It has 168 chromosomes and differs from most crustaceans in that its blood contains hemoglobin.

The largest order of CRUSTACEA, comprising over 10,000 species. They are characterized by three pairs of thoracic appendages modified as maxillipeds, and five pairs of thoracic legs. The order includes the familiar shrimps, crayfish (ASTACOIDEA), true crabs (BRACHYURA), and lobsters (NEPHROPIDAE and PALINURIDAE), among others.

The capability of producing yolk-filled eggs that hatch within the body, so that the young are born alive, but without placental attachment. This applies to certain species of REPTILES and FISHES.

The developmental entity of a fertilized egg (ZYGOTE) in animal species other than MAMMALS. For chickens, use CHICK EMBRYO.