Medusa Worms
Medusa Worms - I saw a large one for sale at a LFS for $30. It looked pretty cool, but also pretty large - like a foot long or more. Is it basically a sand-eating cuke? Or is it a filter feeder?
Yes, many of these species get quite large. The Caribbean Euapta averages about 3ft as an adult, and some of the Indopacific species can be even longer (~5 ft). They are active animals, and rapidly crawl about the tank at night while feeding -- this can be a problem for sensitive corals because their bodies, although lacking tube feet, are covered in hook-like projections of the body wall ossicles. Although generally not a problem, these hooks are used in locomotion, and can catch and tear the tissue of animals (including the cuke itself -- especially during shipping), especially if the cuke is startled and retracts suddenly.
No they are definitely not filter-feeders. Some species appear to be commensals of sponges, gaining at least some of their nutrition from sponge waste products, but in general all these apodid cukes are feeding on organic detritus collected from surface sediments (and I assume any imported for the pet trade are of the latter category). They generally spend their days hiding in the rock structure of the reef and only emerge at night. I always worry that reports of them being active during the day is an indication of starvation, and that the animals are so hungry that their natural tendency to hide during the day is overwhelmed by their need to feed, so they roam the tank day and night in search of food. It is rare to see one out before dusk in the wild, and according to Hammond (1982) they only feed at night even if they are seen during the daylight hours (this is likely not true of starving animals in the aquarium). At dusk they emerge from hiding and forage the sand, coral rubble and seagrass beds until dawn - most do not stay on the reef proper (except the sponge commensals). They generally feed by slapping their tentacles onto the surface and ingesting sediments and detritus from all surfaces in which they come in contact. They process a *lot* of sediments -- animals collected during daylight hours were found to have completely empty digestive tracts, and examination of the feeding showed that these animals pass food completely through their gut within about an hour. Given that, they need a lot of sediments organic-rich sediments to sustain themselves, and unless you have a very well-established and relatively large tank that has live sand and a reasonably high bioload, these animals are a poor bet for survival in your tank....
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