Tanaidacea

Tanaidacea, commonly known as tanaids, are an order of small, benthic crustaceans within the class Malacostraca and the larger grouping Peracarida. They are distributed worldwide, primarily in marine environments, inhabiting sand, mud, coral, and seagrass beds as well as the deep sea. Some species occur in brackish waters, and a few have been reported from freshwater systems. Most tanaids are diminutive, typically a few millimeters to about a centimeter in length, with an elongated body that includes a distinct cephalon shield and a narrow, segmented trunk.

Morphology and life cycle: Tanaids have a cephalon and a segmented thorax, with thoracic pereopods used for locomotion and feeding. The abdomen is often slender and may bear reduced pleopods, terminating in a small tail region. A characteristic feature is the female marsupial brood pouch, formed by specialized plates on the thoracic appendages (oostegites), in which eggs are carried until hatching. Development is generally direct, with juveniles resembling miniature adults, though some species may exhibit short larval stages within the pouch.

Ecology and systematics: Tanaids typically feed on detritus, microbes, and small organisms, employing a range of feeding strategies from scavenging to suspension feeding. They are common residents of sedimentary habitats, often constructing burrows or living among tubes and algal mats. They constitute a diverse and widespread component of benthic communities. Taxonomic work on Tanaidacea comprises multiple families and genera, with ongoing revisions aided by both traditional morphology and molecular data.