invertebratescrustaceans

Crustaceans are a diverse group of primarily aquatic invertebrates belonging to the subphylum Crustacea within the phylum Arthropoda. They range from microscopic copepods to large lobsters and include familiar forms such as crabs, lobsters, shrimp, crayfish, barnacles, and krill.

Crustaceans display a variety of forms but share certain features: a segmented body usually covered by a calcified or chitinous exoskeleton; two pairs of antennae; paired biramous appendages; and gills in many aquatic species. Most crustaceans grow by molting their exoskeletons.

Taxonomically, crustaceans are divided into several major lineages, including Malacostraca (crabs, lobsters, shrimp, krill), Branchiopoda (water fleas and fairy shrimp), and Maxillopoda (barnacles, copepods, ostracods). There are tens of thousands of described species, occupying marine, freshwater, and, in some cases, terrestrial habitats.

Ecology and life history: They occupy nearly every aquatic niche, acting as detritivores, herbivores, filter feeders, grazers, and predators. They are crucial members of aquatic food webs and support many commercially important fisheries and aquaculture species. Some crustaceans, such as barnacles, are epibionts on other animals, while others, like krill, form dense swarms that feed larger predators.

Reproduction and development: Most crustaceans reproduce sexually, with a variety of mating systems. Many have complex life cycles that include free-swimming larval stages such as nauplius or zoea, while others develop directly. Parental care is known in some groups.