Pineapple sea cucumber

One of the largest sea cucumbers in the region, commonly 50 to 70 cm and occasionally more, and heavy with it. The body is orange to red-brown, roughly square in cross-section, and the upper surface is covered in large soft papillae arranged in groups of three or four with their bases fused, so each cluster reads as a blunt star; that texture is where the pineapple and prickly redfish names come from and it separates the species from everything else on a sand slope. The underside is flat and pale, densely set with tube feet. It has no Cuvierian tubules, so it does not eject sticky white threads when handled, which is one of the few practical differences from Pearsonothuria graeffei.

It is a deposit feeder, taking in sand at one end, stripping the organic film and passing clean sediment out at the other in coiled casts. Its size makes it the best of the local sea cucumbers to search for associates: the scale worm Gastrolepidia clavigera rides the body wall and flanks, the emperor shrimp Zenopontonia rex and the sea cucumber crab Lissocarcinus orbicularis are usually on the underside or near the anal opening, and large holothurians of this kind are among the hosts of pearlfishes, which live in the respiratory tree and back in through the anus at dawn. Almost nothing is visible from directly above, and the animal has to be looked along and under.

It is worth saying that this is a fished species. Thelenota ananas is one of the highest-value beche-de-mer species and has been taken hard across Indonesia and the Philippines; it is listed as Endangered on the IUCN Red List, and how often a diver sees one now depends mainly on how close the site is to a fishing community rather than on the habitat.