Crustacee

Crustacee refers to crustaceans, a large and diverse group of arthropods within the subphylum Crustacea. They are predominantly aquatic, living in oceans, rivers, and lakes, with some species adapted to moist terrestrial habitats such as leaf litter and soil. Members range from microscopic copepods to the largest lobsters and are essential components of many ecosystems.

Anatomically, crustacee typically have a chitinous exoskeleton that they molt to grow, and bodies often divided into a head and trunk, sometimes forming a cephalothorax. Most possess two pairs of antennae and paired biramous appendages used for walking, swimming, feeding, and sensing the environment. In aquatic forms, respiration is usually through gills, though some species exchange gases across the body surface. They have an open circulatory system with a dorsal heart and hemolymph that bathes tissues.

Crustacee are divided into several major groups, including Malacostraca (crabs, lobsters, shrimp, krill), Branchiopoda (water fleas, brine shrimp), Ostracoda (seed shrimp), Copepoda, and Maxillopoda. They exhibit a wide range of life cycles; many marine species have free-living larval stages such as nauplius, zoea, and mysis, while others develop directly into juveniles. Their ecological roles are diverse, including predators, scavengers, filter feeders, and parasites, and they form foundational links in many food webs.

Humans rely on crustacee for food, with fisheries and aquaculture targeting shrimp, crabs, and lobsters. They are also used in research and education as model organisms and contribute to nutrient cycles and ecosystem functioning. Ongoing threats include overfishing, habitat degradation, and climate-induced changes in distribution and abundance.