Psychropotidae

Psychropotidae is a family of deep-sea swimming sea cucumbers. The geographic range of some psychropotids is very extensive at abyssal depths, whereas other species are found within more restricted ranges.

==Description== "Psychropotidae are elongate in shape, with the anterior part of the dorsal surface depressed. Many psychropotids have a large posterior appendage. They usually have 10-20 tentacles and ventrolateral radii, each with a single row of many small tube feet." Like all holothurians, psychropotids have calcareous deposits, vestigial elements of the usual Echinoderm skeleton. "In psychropotids, These are essentially similar to other Holothuroidea, differing in a very low degree of calcification", instead consisting mainly of connective tissue. The calcareous ring and spicules of Holothuroidea are useful in determining phylogeny, as they vary greatly and are believed to have evolved independently as species adapted to various biotopes. In psychropotidae there are usually four armed spicules with arms projecting inward and a single large central process projecting outwards. The calcareous ring is incomplete and has 5 independent parts. "The longitudinal axis of sclerites in papillae is transverse to the longitudinal axis of the papilla". "Concave sclerites of Laetmogonidae are probably homologous to concave cruciform sclerites of Elpidiidae and Psychropotidae". Sclerites can be absent in some specimens of the species Benthodytes typica and Benthodytes sanguinolenta. "In Elasipodida all three mesenteries suspending the intestine in the anterior and middle part of the body are attached to the body wall dorsally and only in the posterior part of the body, the mesentery holding the second descending part of the intestine enters the right ventral interradius and is attached to the body wall near the mediadorsal muscular band".