Jaeger, 1833 
Holothuria atra, commonly known as the black sea cucumber or lollyfish, is a species of marine invertebrate in the family Holothuriidae. It was placed in the subgenus Halodeima by Pearson in 1914, making its full scientific name Holothuria (Halodeima) atra. It is the type species of the subgenus.
Holothuria atra is a sausage-shaped sea cucumber that can grow to a length of 60 centimetres (24 in) but 20 centimetres (7.9 in) is a more common size. It has a smooth, pliable, entirely black skin which often has sand adhering to it, especially in smaller individuals. The mouth is on the underside at one end and is surrounded by a fringe of 20, black, branched tentacles. The anus is at the other end.
Distribution and habitat
Holothuria atra is found in the tropical Indo-Pacific region, its range 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 seagrass meadows at depths of up to 20 metres (66 ft). Its colouring makes it conspicuous but it is very often camouflaged by a coating of sand which may also serve to keep it cool by protecting it from the sun's rays. It favours 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 retreats. In such places it is often found in pools above the low tide mark which are warmed by the sun during the day. Holothuria atra seems to tolerate these high temperatures well and individuals appeared healthy and were feeding when the water temperature rose as high as 39 °C.
Holothuria atra is an omnivore, sifting through the sediment with its tentacles and feeding on detritus and other organic matter. It ingests sand at the same time and digests the biofilm on the sand grains before ejecting them through its anus.
As a defence against predators, Holothuria atra emits a toxic red fluid when its skin is rubbed or damaged. When attacked, it does not eject Cuvierian tubules in the way that some sea cucumbers do, but instead extrudes its internal organs through its anus. These are also toxic and this sea cucumber is not recommended to be kept in a reef aquarium because the water may become toxic to its other animal occupants.
It is not possible to distinguish between male and female Holothuria atra externally. Maturity is reached at a body length of about 16 centimetres (6.3 in) and spawning mostly takes place during the summer and autumn although in equatorial waters it may take place all year round. Holothuria atra is also fissiparous, meaning that 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. No sand adheres to the newly separated surfaces as there are no tube feet present to retain the grains.
Holothuria atra is often found associated with the polychaete worm Gastrolepidia clavigera, a black worm which crawls about over the sea cucumber's skin. Holothuria atra seems to have few natural predators.
In the Pacific Islands, Holothuria atra is collected by diving or by wading at low tide, and used for human consumption; its commercial value, however, is low.
- Conand, C.; Purcell, S. & Gamboa, R. (2010). "Holothuria atra". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 29 October 2016.
- Paulay, Gustav (2010). "Holothuria (Halodeima) atra Jaeger, 1833". World Register of Marine Species. Retrieved 2012-01-20.
- Holothuria atra Marine Species Identification Portal. Retrieved 2012-01-20.
- Holothuria atra Jaeger, 1833. SeaLifeBase. Retrieved 2012-01-20.
- Ecological Observations on the Sea Cucumbers Holothuria atra and H. leucospilota at Rongelap Atoll, Marshall Islands Retrieved 2012-01-20.
- Black Sea Cucumber (Holothuria atra) Saltwater Aquariums. Retrieved 2012-01-20.
- Abdel-Razek, F.A.; et al. (2005). "Reproductive biology of the tropical sea cucumber Holothuria atra (Echinodermata: Holothuroidea) in the Red Sea coast of Egypt" (PDF). Egyptian Journal of Aquatic Research. 31 (2): 383–402.
- C. Conand, Asexual reproduction by fission in Holothuria atra: variability of some parameters in populations from the tropical Indo-Pacific, Oceanologica acta, 1996, vol. 19, no 3-4, pp. 189-475 (29 ref.), pp. 209-216.
- The relationship between holothurians and the portulid crab Lissocarcinus orbicularis