Black Sea Cucumber Holothuria atra/H. forskali/H. leucospilota

The Black Sea Cucumber, H. atra, is native to the ocean floor around reefs in the Indo-WestPacific. The name cucumber relates to the shape and black sea to its colour and habitat, not to the inland waterbody of the Black Sea. They can grow typically to some 20cm long but can reach 60cm. Two other species are also called the Black Sea Cucumber: H. leucospilota/H. (Mertensiothuria) leucospilota, the Black Long Sea Cucumber or Black Tarzan inhabits the same region and grows to 40cm; and H. forskali, the Atlantic Black Sea Cucumber or the Cotton Spinner (see more below).

They have small tentacles at the mouth end and are often covered in sand or debris. Sea cucumbers have a very important job: they eat detritus and waste, scooping it up with sand, and poop it out as clean sand, cleaning up the world's oceans. Usually soft bodied, Black Sea Cucumbers can harden their body to a stiff, fibrous state when threatened. They can also release a toxic, distasteful red fluid if threatened by predators. Some of the chemicals in the toxin or animal may have biomedical uses. Like other sea cucumbers, they are over-harvested as human food.

The cucumber immediately above left and centre is thought to be the Atlantic Black Sea Cucumber or the Cotton Spinner, H. forskali, which grows to 30cm long and is native to the warm eastern Atlantic including the Mediterranean and the Canary Islands. The latter can be dark brown and can have yellow mottling. The "cotton spinner" name relates to a defence mechanism of all sea cucumbers: they can expel a mass of thin, sticky internal organs (Cuvierian tubules) to entangle and slow down a predator while they escape; the tubules will regrow.