Parastichopus regalis

Lore & Background

Parastichopus regalis grows to a length of about 20 cm. Its body is soft and somewhat flattened, with a clearly incised lateral fold bearing large papillae separating the dorsal and ventral surfaces. The dorsal surface is mottled brown, while the ventral surface is paler with a darker longitudinal streak in the center. The integument is strengthened by bony sclerites including tables, terminal plates, and perforated plates; the tentacles surrounding the mouth contain elongated, branched, perforated, and arched rods.

This species is found in the Mediterranean Sea, along African coasts in the eastern Atlantic, and in the tropical and subtropical western Atlantic including the Gulf of Mexico. It typically inhabits sand or other soft substrates at depths down to about 800 m, being most common between 100 and 300 m.

In a commensal arrangement, Parastichopus regalis often hosts the pearlfish Carapus acus, which enters the sea cucumber's respiratory tree via its anus. The fish lives inside during the day and emerges at night to feed. Two fish may occupy a single host, and a pair have been known to breed inside their host. When stressed, the sea cucumber autotomises its internal organs, regenerating them later.

Reader's Guide

Parastichopus regalis is a common species in its range. It is edible and eaten in parts of its range but is not a targeted species, being caught as bycatch during deepwater trawling. Its most notable ecological feature is its commensal relationship with the pearlfish Carapus acus, which uses the sea cucumber's respiratory tree as a daytime refuge and breeding site. This behavior highlights the species' role as a mobile shelter in deepwater soft-substrate habitats. The sea cucumber's ability to autotomise and regenerate its internal organs when stressed is a key survival adaptation. Although not commercially targeted, its occurrence as bycatch in deepwater trawling indicates some human impact. The species' wide distribution across the Atlantic and Mediterranean, combined with its distinctive morphology—including mottled brown dorsal coloration, paler ventral surface with a dark streak, and specialized sclerites—makes it a recognizable member of the Stichopodidae family. Its presence at depths down to 800 m and common occurrence between 100 and 300 m places it in a depth zone frequently affected by deepwater fishing activities.

Did You Know?

• When stressed, Parastichopus regalis autotomises its internal organs and regenerates them later.
• This sea cucumber is caught as bycatch during deepwater trawling.