Eupentacta quinquesemita is a species of sea cucumber, a marine invertebrate with an elongated body, a leathery skin and tentacles surrounding the mouth.

The larvae of a parasitic snail, Thyonicola americana, enter in this way and develop into adults which invade the viscera while maintaining a connection to the gut lumen to release offspring.

The sea cucumber is preyed on by several species of starfish, such as Solaster stimpsoni, Pycnopodia helianthoides and Leptasterias hexactis, and fish such as the kelp greenling (Hexagrammos decagrammus).

[3] This sea cucumber exhibits a seasonal pattern of evisceration, expelling its guts in the autumn and growing a new set in the spring, resulting in a high proportion of T. americana parasites not completing their life cycle, but not all individuals do this.

[5] Breeding takes place between March and May, females liberating large, yolky eggs into the sea where they are fertilised by sperm produced by the males.