Synaptidae is a family of sea cucumbers that have no tube feet, tentacle ampullae, retractor muscles, respiratory trees, or cuvierian tubules. They also lack radial canals of the water-vascular system, with only the circumoral ring present.

Synaptids have elongated bodies, and their size varies significantly from small to quite large. Synapta maculata grows to two metres in length. They are quite active, moving by means of waves of peristaltic contractions. Their tegument is somewhat sticky because of the anchor-like spicules that project through the skin.

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