what is an ascidians
Ascidiacea (commonly known as the ascidians or sea squirts) is a class in the subphylum Tunicata of sac-like marine invertebrate filter feeders. Ascidians are characterized by a tough outer tunic made of the polysaccharide tunicin, as compared to other tunicates which are less rigid. Ascidians are found all over the world, usually in shallow water with salinities over 2.5%.