Atlantic Black Sea Cucumber

This sea cucumber has a cylindrical body and can grow to thirty centimetres long. It is usually deep brown or black but sometimes has an underlying yellowish mottling, especially on the underside. The skin is soft yet coarse and tough and is covered with fleshy papillae which are often tipped with white. The papillae are believed to be sensory organs sensitive to touch and possibly to chemicals dissolved in the water. The underside has three rows of tube feet for walking and climbing while the upper side has two rows of rudimentary suckers. The anterior end has a bunch of twenty yellowish short, retractable tentacles encircling the mouth. At the posterior, inside the body cavity, there are a bundle of Cuvierian tubules or cotton glands which can be ejected as a tangle of sticky white threads to confuse or enmesh predators.

The black sea cucumber occurs around the Atlantic coasts of northwest Europe, the Canary Islands, the Azores and in the Mediterranean Sea. It is found on boulders and rocks, particularly vertical surfaces, from the intertidal zone down to a depth of about fifty metres.

The parasitic copepod Asterocheres boecki is an endoparasite of the black sea cucumber.

It has been found that twenty-six saponins (triterpene glycosides) are present in the Cuvierian tubules and twelve in the animal's body wall. During stressful times, such as the presence of a predator, saponins are released into the surrounding water. It is thought that, though these are insufficient to harm a potential predator, they may serve as a warning that the cucumber is unpalatable.