Euapta godeffroyi

Not recommended: Meerwasser-Lexikon knows of no case of it being kept in captivity. The 'medusa worms' in the trade are almost impossible to identify without an expert, and many synaptids are specialised feeders that an aquarium cannot feed; Rob Toonen advises against buying one unless you know what it eats.

If you have one: a large, established reef tank with a deep sand bed, plenty of fine detritus and coral rubble to anchor in by day. Acclimation: sea cucumbers are sensitive to changes in salinity. Acclimate it slowly by drip in a separate container, then move it without pouring the shipping water into the tank. Handle it as little as possible and with gloves: handling or relocating it can by itself trigger the release of holothurin.

Its tiny anchor-shaped ossicles snag on everything they touch: when the animal suddenly retracts, they can tear or injure the tissue of a coral it was lying on and dislodge loosely fixed frags. Toxicity: synaptids have neither a respiratory tree nor Cuvierian tubules and are said to be relatively non-toxic, but their skin holds distasteful compounds and they are reported to be highly toxic to fish when seriously injured, for example shredded in a pump or against an overflow grate.

Fit every pump, powerhead and overflow intake with a large, securely fixed strainer: according to Rob Toonen, most 'cuke nukes' happen when a sea cucumber is sucked in and shredded. If it happens anyway, remove the animal at once, make a large water change, increase skimming and add activated carbon.

Like other invertebrates, it tolerates neither copper treatments nor high nitrate; never put it in a copper-treated tank, not even in quarantine. For you: its ossicles hook into skin and fabric, sometimes so firmly that it is hard to get free; handle it with gloves, under water.

A nocturnal deposit feeder: it dabs the sediment with its sticky tentacles, keeps the most nutritious particles and lives on organic detritus. Synaptids are the most active sea cucumbers and need a lot of food: their tentacles constantly dab the substrate, ingested particles pass through in about an hour, and they only really feed at night. A synaptid active in broad daylight in an aquarium is not necessarily eating, and may be starving.