Synallactida

Synallactida is a rankless clade of sea cucumbers, but is referred to as an order. Taxa within Synallactida were previously classified in an order called Aspidochirotida, which was determined to be polyphyletic in 2017.

List of families
Synallactida includes over 130 species in three extant families and two extinct genera:
 * Deimatidae Théel, 1882 – 3 genera
 * Stichopodidae Haeckel, 1896 – 9 genera
 * Synallactidae Ludwig, 1894 – 12 genera
 * Genus †Collbatothuria Smith & Gallemí, 1991
 * Genus †Tribrachiodemas Reich, 2010