Pearsonothuria is agenus of sea cucumbers in thefamilyHolothuriidae.Pearsonothuria graeffei is the onlyspecies in the genus.^[3]Graeffe's sea cucumber is found in the tropicalIndo-Pacific Ocean and thetype locality is Viti Island,Fiji.^[2] It is named afterEduard Heinrich Graeffe, Semper's coworker at theMuseum Godeffroy.

Pearsonothuria graeffei
Pearsonothuria graeffei in theMaldives
Conservation status
Least Concern (IUCN 3.1)[1]
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Echinodermata
Class:	Holothuroidea
Order:	Holothuriida
Family:	Holothuriidae
Genus:	Pearsonothuria Levin, 1984[3]
Species:	P. graeffei
Binomial name
Pearsonothuria graeffei Semper, 1868[2]
Synonyms[2]
Bohadschia drachi Cherbonnier, 1954 Bohadschia graeffei (Semper, 1868) Holothuria graffei Semper, 1868 Stichopus troschelii Müller, 1854

Pearsonothuria graeffei is a roughly cylindrical, thin-walled sea cucumber that grows to about 30 centimetres (12 in) in length.^[4] Its mouth, at one end, is surrounded by a ring of up to 24 leaf-like, paddle-shaped tentacles with black stalks which are black on the upper side and white beneath. The anus is at the other end of the body and there are several rows oftube feet along the underside. The colour of the adults is pale brown and white, with black speckles and small thornlike protuberances.

By contrast, the juveniles are brightly coloured, being white and blue or black, with a few large, yellow, thornlike projections. This colouration makes them closely resemble thesea slug,Phyllidia varicosa, the bright colours of which warnpredators of itstoxicity. The appearance of the juvenile sea cucumbers begins to change when they grow larger than the slug and themimicry is no longer effective.^[5]

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  A live juvenile individual of Pearsonothuria graeffei,in situ offMadagascar
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  Adult specimen in theMaldives
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  Close-up on the tentacles
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  Sperm release during a mass spawning event on the island of Koh Tao, Thailand

Pearsonothuria graeffei is found in tropical parts of theIndo-Pacific Ocean. The range extends from the east coast of Africa to thePhilippines,Indonesia and the South Pacific. It is found on the seabed and on coral reefs at depths down to about 25 metres (82 ft).^[2][4]

Pearsonothuria graeffei is ascavenger and roams around on the seabed sifting through the sediment with its feeding tentacles. Any organic matter it finds is passed to its mouth by the tentacles.^[6] Its daily activities start within a few minutes of dawn and continue until half an hour after sunset after which time it adopts an inactive stance with its rear end raised and its tentacles retracted into its mouth. It then remains immobile during the night.^[7] They are known to spawn simultaneously with other Echinoderms, including thecrown-of-thorns starfish and the sea urchinDiadema setosum.^[8]

When threatened or disturbed, many sea cucumbers ejectcuvierian tubules, thin white sticky strands of viscera, from theircloacas.Pearsonothuria graeffei seems reluctant to do this except under conditions of extreme stress. The threads of this species containglycosides that are toxic to the aggressor. The effect of theseneuro-toxins is to prevent nerve impulses being transmitted, an effect similar to that produced bycocaine. The chemicals,echinoside A andds-echinoside A, are being investigated for their possible use by humans aspainkillers or anti-tumour drugs.^[5] Experimentsin vitro show that they have marked anti-cancer activity inHep G2 cells and that, when given to mice with H22hepatocellular carcinoma tumours (liver cancer), the weight of the tumours was reduced by about 50%.^[9]

• Photos ofPearsonothuria on Sealife Collection