| Holothuria atra | |
|---|---|
 | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Echinodermata |
| Class: | Holothuroidea |
| Order: | Holothuriida |
| Family: | Holothuriidae |
| Genus: | Holothuria |
| Species: | H. atra |
| Binomial name | |
| Holothuria atra | |
| Synonyms[2] | |
| |
Holothuria atra, commonly known as theblack sea cucumber orlollyfish, is aspecies of marineinvertebrate in the familyHolothuriidae. It was placed in the subgenusHalodeima by Pearson in 1914, making its full scientific nameHolothuria (Halodeima) atra. It is thetype species of the subgenus.[2]
Holothuria atra is asea 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, branchedtentacles. The anus is at the other end.[3][4]
Holothuria atra is found in the tropicalIndo-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 inseagrass meadows at depths of up to 20 metres (66 ft).[2][3] Its colouring makes it conspicuous but it is very oftencamouflaged 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.[5]
Holothuria atra is anomnivore, sifting through the sediment with its tentacles and feeding ondetritus and other organic matter. As a defence againstpredators,Holothuria atra emits a toxic red fluid when its skin is rubbed or damaged.[3] When attacked, it does not ejectCuvierian tubules in the way that some sea cucumbers do, but instead extrudes its internal organs through its anus.
It is not possible to distinguish between male and femaleHolothuria 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.[6] It takes a minimum of 18-25 days forHolothuria atra to reachnatural competence.[7]Holothuria atra is alsofissiparous, meaning that it can reproduce by transverse fission.[4][8] It is mostly smaller individuals which 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.[5] No sand adheres to the newly separated surfaces as there are no tube feet present to retain the grains.[5]
Holothuria atra, like manyechinoderms, engage in sedimentbioturbation—a process which plays an important role in the health of coral reefs.[9]Holothuria atra is often found associated with thepolychaete wormGastrolepidia clavigera, a black worm which crawls about over the sea cucumber's skin.[2]Holothuria atra seems to have few naturalpredators.[5]
Lissocarcinus orbicularis, a small crab, is known to live on this species in acommensal relationship.[10]
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.[4] OnGuam, the toxic red fluid thatHolothuria atra releases is utilized to drive octopuses out of hiding holes.[11]
Compounds of potential biomedical importance are present inHolothuria atra, includinglectin, steroidal sapogenins and triterpene glycoside.[12]
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