Phallusia nigra is a solitary marine tunicate of the ascidian class found in tropical seas around the world. It usually lives in shallow waters, attached to any hard substrate. Like all tunicates, P. nigra has a thick leathery envelope (tunic) containing cellulosic material. Like all solitary ascidians, the tunic encloses a sac-shaped body with separate water entrance and exit tubes (siphons). It lives on plankton that it filters from seawater with a mucous net.