Pearsonothuria

Lore & Background

Pearsonothuria graeffei is a roughly cylindrical, thin-walled sea cucumber that grows to about 30 centimetres in length. Its mouth is surrounded by up to 24 leaf-like, paddle-shaped tentacles with black stalks that are black on the upper side and white beneath. The anus is at the opposite end, and several rows of tube feet run along the underside. Adults are pale brown and white with black speckles and small thornlike protuberances. Juveniles are brightly colored white and blue or black, with a few large, yellow, thornlike projections, closely resembling the sea slug Phyllidia varicosa, whose bright colors warn predators of its toxicity. The juvenile appearance changes when they grow larger than the slug and the mimicry is no longer effective. The species is named after Eduard Heinrich Graeffe, Semper's coworker at the Museum Godeffroy, and the type locality is Viti Island, Fiji.

Reader's Guide

Pearsonothuria graeffei is a scavenger that roams the seabed sifting sediment with its feeding tentacles, passing organic matter to its mouth. Its daily activity begins within a few minutes of dawn and continues until half an hour after sunset, after which it adopts an inactive stance with its rear end raised and tentacles retracted, remaining immobile through the night. It is known to spawn simultaneously with other echinoderms, including the crown-of-thorns starfish and the sea urchin Diadema setosum. When threatened, many sea cucumbers eject cuvierian tubules, but Pearsonothuria graeffei seems reluctant to do so except under extreme stress. The threads contain glycosides that are toxic to aggressors, with neurotoxins that prevent nerve impulse transmission, an effect similar to cocaine. The chemicals echinoside A and ds-echinoside A are being investigated for possible use as painkillers or anti-tumor drugs. In vitro experiments show marked anti-cancer activity in Hep G2 cells, and when given to mice with H22 hepatocellular carcinoma tumors, tumor weight was reduced by about 50%.

Did You Know?

• Pearsonothuria graeffei is the only species in the genus Pearsonothuria.
• Juveniles mimic the toxic sea slug Phyllidia varicosa in coloration.
• Its cuvierian tubules contain glycosides that block nerve impulses, similar to cocaine.
• The chemicals echinoside A and ds-echinoside A reduced liver tumor weight in mice by about 50%.