Black sea cucumber. I think the sand-sifting variety are similar, but you do want the black ones specifically (they basically look like a long turd with no spikes).is it a certain type of black sea cucumber or just a black sea cucumber
Here is what oceans garden has
Sand Sifting Sea Cucumber - Oceans Garden Aquaculture
Cucumbers are notorious for cleaning the sand bed of coral reefs and rock reefs eating detritus. They move along aerating the sand and release debris andwww.oceansgarden.com