Holothuria poli

Holothuria poli is found in the East Atlantic Ocean, between the Canary Islands and the Bay of Biscay, in the Mediterranean Sea and in the Red Sea; its occurrence in the Red Sea is likely as a result of its larvae passing through the Suez Canal,^[3] a process known as anti-Lessepsian migration. It inhabits the seabed, usually at depths down to about 20 m (70 ft), but has been observed on a muddy substrate off the coast of Tunisia at much greater depths (80 to 250 m (260 to 820 ft)). It is found on sand or rock, and favours seagrass meadows and areas with green seaweed such as Caulerpa.^[3]

Holothuria poli is a limnivore, using the tentacles round its mouth to gather up sediment and shovelling this detritus into its mouth. The material is sorted in the gut, with organic particles being digested while sand and other indigestible material is mixed with mucus and formed into balls which are voided in a string of balls through the anus. In this way, it has been calculated that the sea cucumbers in a square metre of sand can "process" nearly 20 kg (44 lb) of sediment in a year. This sea cucumber is sometimes parasitised by the worm-like sea snail Entoconcha mirabilis. It has few predators because of the thick leathery skin and the presence of the bony sclerites in the integument.^[3]

The sexes are separate in this species and reproduction takes place between November and January. The animals rear up, adopting L-shaped postures, to release clouds of gametes into the water column; there seems to be some sort of synchronisation mechanism for this release. The larvae are planktonic and pass through several stages before settling on the seabed and undergoing metamorphosis into juveniles.^[3]