Holothuria hilla

Holothuria hilla belongs to the subgenus Mertensiothuria within the genus Holothuria. It goes by several common names: contractile sea cucumber, sand sifting sea cucumber, tigertail sea cucumber, and, in Hawaii, light spotted sea cucumber. Its range covers the Indo-Pacific region and the Red Sea.

Description

This sea cucumber has a cylindrical body that tapers slightly at the rear, reaching about 40 cm in length and 5 cm in diameter. Its skin is thin, soft, and wrinkled. On the dorsal side, rows of tube feet are modified into thornlike, conical papillae with broad bases, sometimes paired. These papillae are creamy-white, standing out against a pinkish, golden, or brown background.

The ventral side is similarly colored, but its papillae are longer, yellowish, and arranged in four or five rows. The mouth, located on the underside, is ringed by twenty yellowish, peltate tentacles. Although it possesses Cuvierian tubules, it does not expel them defensively like some other species.

Distribution and habitat

The species lives in the Red Sea, Persian Gulf, and across the tropical west and central Indo-Pacific, reaching as far east as Hawaii and even Panama. It is most common at depths less than 30 m, though it can occur down to 200 m. Its habitats include sandy, rocky, and coral substrates, as well as lagoons, seagrass meadows, and flat areas.

Ecology

As a detritivore, H. hilla scoops sand into its mouth with its oral tentacles, digests bacteria and organic particles, and expels the cleaned sand through its anus, thereby churning large areas of the seabed. Reproduction can be sexual, with males and females releasing gametes into the water, or asexual, through fission.

Sexual reproduction tends to occur during hotter periods, while fission is more common in cooler weather. In Réunion, where the species is rare, only fission has been observed. During fission, the animal stops feeding and hides; the missing parts regenerate, often appearing paler than the original sections.