amfipoder

Amphipods are small crustaceans that form the order Amphipoda within the class Malacostraca. The name derives from Greek amphi- “on both sides” and pod “foot.” With thousands of described species, amphipods occupy a wide range of habitats and morphologies, from delicate forms to robust scavengers, and are found in marine, freshwater, and some terrestrial environments worldwide.

Typically, an amphipod's body is laterally compressed and lacks a carapace. It has a head, a flexible thorax with walking legs, and a segmented abdomen ending in uropods and a telson. Two pairs of antennae are present, and gnathopods and other appendages vary among species. Most species are small, usually a few millimeters to a few centimeters long.

Amphipods inhabit benthic sediments, seagrass beds, interstitial spaces, cave systems, and leaf litter in terrestrial settings. They can be detritivores, herbivores, scavengers, or predators, contributing to nutrient cycling. They are important prey for fish and birds and are often used as bioindicators of water quality. Some species live as commensals or parasites on other invertebrates or fishes.

Reproduction is sexual. Females carry eggs in a brood pouch beneath the thoracic legs until hatching. In many species, young hatch as mancae that resemble small adults (direct development). Lifecycle strategies vary, and some forms show parental care. The group is cosmopolitan, with many native species and several invasive ones that can influence local aquatic communities.