Holothuriida

Lore & Background

Holothuriida is an order of sea cucumbers distinguished from other sea cucumbers by the presence of flattened, often leaf-like tentacles, but without the other large appendages found in the related order Elasipodida. They do not have introvert or retractor muscles. The tube feet often form a clearly demarcated sole. They have 15-30 shield-shaped retractile tentacles surrounding their mouths. The body wall is thick and leathery and contains ossicles, including some table-shaped ones. They have respiratory trees for gas exchange. The mesentery of the posterior loop of their gut is attached to the right ventral interradius. The muscles that run longitudinally down the body are arranged into five double bands. They can emit sticky white threads known as cuvierian tubules from their cloacas in order to distract or entangle predators. They are usually found in exposed shallow-water environments.

Reader's Guide

The order Holothuriida is notable for its taxonomic history: taxa within it were previously classified in the order Aspidochirotida, which was determined to be polyphyletic in 2017. Some taxa were also reclassified into the clades Synallactida and Persiculida. The order includes two families: Holothuriidae, with 5 genera and over 200 species, and Mesothuriidae, with 2 genera and 32 species. Their popularity as luxury seafood in some Asian countries poses a serious threat to the order. Their distinctive features include flattened leaf-like tentacles, a thick leathery body wall with table-shaped ossicles, and the ability to emit sticky white cuvierian tubules from their cloacas as a defense mechanism. They are typically found in exposed shallow-water environments.

Did You Know?

• Holothuriida species emit sticky white threads called cuvierian tubules from their cloacas to distract predators.
• The order has 15-30 shield-shaped retractile tentacles surrounding the mouth.
• Their body wall is thick and leathery and contains table-shaped ossicles.