Holothuria tubulosa

Holothuria tubulosa, also called the cotton-spinner or tubular sea cucumber, belongs to the family Holothuriidae. It serves as the type species for the genus Holothuria and is classified within the subgenus Holothuria, giving it the full scientific name Holothuria (Holothuria) tubulosa.

Description

This sea cucumber reaches lengths between 20 and 45 centimeters, with a diameter of about 6 centimeters. Its body is roughly cylindrical, with a flattened underside bearing three lengthwise rows of tube feet.

The skin is tough and leathery, typically brown, and covered with many dark, conical, thorn-like bumps called papillae. The animal often appears grayish because it secretes a protective mucus film that attracts bits of seaweed and sediment. At the front end, a fringe of short, flattened tentacles surrounds the mouth, while the anus is at the rear.

Distribution and habitat

The species lives in temperate parts of the eastern Atlantic Ocean, ranging north to the Bay of Biscay, and is abundant in the Mediterranean Sea. It inhabits sandy seabeds, seagrass meadows (especially Posidonia species), and muddy rocks down to depths of about 100 meters.

Biology

Feeding on detritus, algae, and plankton, Holothuria tubulosa moves across surfaces or clings to rocks using its tube feet. Individuals are dioecious—either male or female—but look identical externally. During a mass spawning event observed in the Mediterranean in August 2003, spawning occurred on two afternoons coinciding with the full moon.

Many mature animals reared their front ends upward, leaving only the rear third of their bodies on the seabed. This lifted their genital openings, located just below the mouth, away from the substrate to improve gamete dispersal. First, some individuals (likely males) released a whitish fluid that spread through the water.

Then, fewer individuals (likely females) emitted a thicker fluid, possibly triggered by the male gametes. Each release lasted about 30 minutes. The key conditions for spawning appeared to be a full moon and a sea temperature around 25 °C.

Fertilized eggs hatch in about 24 hours, and the larvae drift as plankton. They feed on microscopic algae, passing through several developmental stages over a few weeks before settling on the seabed and transforming into juveniles.