Apodida
An order of sea cucumbers lacking tube feet and respiratory trees.
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.
Quick Facts
- Taxon
- Apodida
Facts from the source article.
Lore & Background
Apodida are vagile holothurians with an elongated shape, worm or snake-like, adapted for burrowing through sediment, sometimes similar to earthworms. Their mouth is surrounded with 10-25 pinnate or peltate tentacles. The absence of tube feet gives the order its name, Apodida meaning without feet: they move by crawling on the sediment, hence they need flat bottoms with few current. Members of this order have a circum-oral ring and tentacles, but do not have tube feet or radial canals. They also lack the complex respiratory trees found in other sea cucumbers, and respire and excrete nitrogenous waste through their skin. The ossicles, minute calcareous plates embedded in the skin and characteristic of each species, can include wheel and anchor shapes.
Reader's Guide
The order Apodida is notable for its distinctive lack of tube feet, which sets it apart from most other sea cucumbers and gives the group its name. Its members are largely infaunal, burrowing through sediment in a manner similar to earthworms, and can reach lengths up to 3 meters in the species Synapta maculata. The order contains three extant families—Chiridotidae, Myriotrochidae, and Synaptidae—as well as one extinct family, Achistridae. Apodids respire and excrete nitrogenous waste through their skin, lacking the complex respiratory trees found in other sea cucumbers. Their ossicles, which are minute calcareous plates embedded in the skin, can include wheel and anchor shapes, aiding in species identification. The order's dependence on flat bottoms with few current reflects its crawling mode of locomotion.
Did You Know?
- Apodida means 'without feet', referring to the absence of tube feet.
- The species Synapta maculata can reach up to 3 meters in length.
- Their ossicles can include wheel and anchor shapes.
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