exoskeleton made of calcium - no internal skeleton.The head has two compound eyes, two pairs of antennae, and three pairs of mouthparts.A pair of green glands excrete wastes near the base of antennae.The abdominal segments have swimmerets (swimming legs)The SEXES are separate. Eggs are attached to the swimmerets (swimming legs) of the female. The first pair is enlarged in the male (it is used to pass sperm to the female).The tail is fan-shaped, and ends in uropods and a telson.The circulatory system is open; there is no heart and the "blood" is pumped by vessels into sinuses, and does not FLOW in a closed loop).The nervous system consists of a primitive ventral NERVE cord and ganglia system (similar to those of an earthworm).Classification: Kingdom Animalia, Phylum Arthropoda, Subphylum Crustacea, Classes:Class Cephalocarida (primitive, shrimp-like, discovered in 1955) - 9 speciesClass Branchiopoda (with flattened gill-carrying appendages) - about 800 species, including brine shrimp, fairy shrimp, water fleas, etc.Class Malacostraca - 18000 species, including lobsters, shrimp, crabs, woodlice, isopods, amphipods, krill, etc.Class Maxillopoda (ostracods, copepods, barnacles)Class Remipedia (primitive crustaceans discovered in submerged CAVES by JILL Yager in 1980)