isopoden

Isopoda, commonly known as isopods, is an order of crustaceans within the class Malacostraca. The group includes thousands of described species that inhabit a wide range of environments, from marine and freshwater to terrestrial. Terrestrial isopods, often called woodlice or pillbugs, are among the best known representatives.

Isopods have a dorsoventrally flattened body divided into a head, a seven-segmented thorax with paired legs (pereopods), and a segmented abdomen. They lack a carapace and possess two pairs of antennae. The abdomen bears pleopods used for swimming or respiration in many species, and the tail-end carries uropods. Sizes vary greatly, from a few millimeters in small marine forms to tens of centimeters in the largest deep-sea species such as Bathynomus giganteus. Marine isopods typically breathe through gills, while terrestrial species have adapted respiratory structures on the thorax or pleopods, such as pleopodal lungs or pseudotracheae.

Ecology and life history are diverse. Most isopods are detritivores or scavengers, grazing on algae, decaying matter, or invertebrates; many marine species play a role in benthic decomposition and nutrient cycling. A number of isopods are parasitic or commensal, notably families that attach to fish or other crustaceans. Reproduction is sexual; females brood eggs in a marsupial pouch formed by specialized thoracic limbs. The young may hatch as mancae that resemble small adults or undergo additional juvenile stages before reaching maturity.

Human relevance varies by group. Oniscidea (terrestrial woodlice) are common in damp habitats and can indicate environmental moisture levels, while parasitic isopods and certain marine species have ecological and economic importance in their respective systems.