Black Sea Cucumber (Holothuria atra)

Holothuria atra spends its life running the reef tank equivalent of a slow, thorough vacuum pass — ingesting sand a mouthful at a time, stripping out detritus and organic buildup, and leaving cleaner substrate in its wake. It coats itself in a layer of sand grains as it moves, part camouflage and part UV protection, so what looks like a plain black log is usually wearing a light dusting of whatever it just ate. Handle it gently and keep it clear of overflow intakes — like most holothurians it can release sticky Cuvierian tubules, or worse, under serious stress.

Care level: Easy · Temperament: Peaceful · Max size: ~10" · Min tank: 40 gal, mature · Reef safe: Yes · Diet: Detritivore, sifts sand