Black Sea Cucumber, Holothuria atra

The Black Sea Cucumber (Holothuria atra), also known as the Lollyfish, is a species of marine invertebrate in the Holothuriidae family. It is found in the Indo-Pacific ocean region, extending from the Red Sea and East Africa to Australia. It is found on the seabed, in shallow waters on reefs and sand flats and in sea grass meadows at depths up to 66 feet.

It prefers reef flats where it is not fully exposed to the waves but the water is well aerated, and shallows beside slabs of rock from under which cool water wells out when the tide ebbs. In such places it is often found in pools above the low tide mark which are warmed by the sun during the day. It can tolerate higher temperatures well and remain healthy even when the water temperature rise to as high as 102 degrees Fahrenheit.

This is a sausage-shaped sea cucumber that can grow to 24 inches long, although 8 inches is a much more common size. It has a smooth, pliable, entirely black skin which often has sand adhered to it, especially in smaller individuals. The mouth is located on the underside at one end and is surrounded by a fringe of twenty branched tentacles, which are also black. Its coloring makes it very noticeable, but it is very often camouflaged by a coating of sand, which also serves as a coolant, protecting it from the sun’s rays.

The Black Sea Cucumber is an omnivore, sifting through the sediment with its tentacles and feeding on detritus and other organic matter. It ingests sand along with the biofilm on the sand grains before ejecting them through its anus.

Externally, it is impossible to distinguish between the male and female of this species. Maturity is reached at a body length of roughly 6.3 inches and spawning takes place during the summer and autumn, although in equatorial waters it may take place year-round. This sea cucumber is also fissiparous, meaning it can reproduce by transverse fission. It is mostly smaller individuals that divide in this way. A constriction appears, becomes deeper and deeper and after some time the integument separates leaving two relatively wide but short individuals.

The Black Sea Cucumber is often found associated with the polychaete worm Gastrolepidia clavigera, which crawls along the sea cucumber’s skin. This creature has few known natural predators. Yet, it will emit a toxic red fluid when its skin is rubbed or damaged, which acts as a defense against predators.

When attacked, it ejects its internal organs through its anus. These are also toxic and, for this reason, the Black Sea Cucumber is not recommended to be kept in a reef aquarium because the water may become toxic to other occupants. This animal is often used as a food source for humans, however, its commercial value is relatively low.

Image Caption: Black Sea Cucumber, Holothuria atra