Apodida

Apodida is an order of sea cucumbers found from shallow coastal waters to the deep sea, mostly living buried in the sediment. The group includes about 270 known species, grouped into 32 genera and three families. Their name, apodids, means "without feet."

These sea cucumbers are elongated and worm- or snake-like, with some species like Synapta maculata reaching up to three meters. Their shape helps them burrow through sediment, often moving like earthworms. Around the mouth are 10 to 25 feathery or shield-shaped tentacles. Lacking tube feet, they crawl across the seafloor, requiring flat, calm bottoms.

Apodids have a ring of plates around the mouth and tentacles, but no tube feet or radial canals. They also lack the complex respiratory trees found in other sea cucumbers, instead breathing and excreting nitrogen waste through their skin. Their skin contains tiny calcareous plates called ossicles, which are unique to each species and can be shaped like wheels or anchors.

The order includes three living families: Chiridotidae, Myriotrochidae, and Synaptidae, plus the extinct family †Achistridae.