Free-living Echinoderms usually with an elongated, worm- or sausage-shaped body.
Mouth and alimentary canal
They have no free arms, but a circle of tentacles around the mouth. The mouth is located at the anterior end of the body. The oesophagus is surrounded by a calcareous ring. The alimentary canal is long and mostly looped. The anus is usually at the posterior end.
The skeleton generally consists of calcareous deposits (spicules). The tube-feet (if present) are never in a furrow.
- Order Apoda
- Order Dendrochirota