http://en.wikipedia.org/wiki/Ascidiacea
Sea squirts are rounded or cylindrical animals ranging from about 0.5 to 10 centimetres (0.20 to 3.94 in) in size. One end of the body is always firmly fixed to rock, coral, or some similar solid surface. The lower surface is pitted or ridged, and in some species has root-like extensions that help the animal grip onto the surface. The body wall is covered by a smooth thick tunic, which is often quite rigid. The tunic consists of a cellulose-like substance called tunicin along with proteins and calcium salts. Unlike the shells of molluscs, the tunic is composed of living tissue, and often has its own blood supply. In some colonial species, the tunics of adjacent individuals are fused into a single structure.
Sea squirts are rounded or cylindrical animals ranging from about 0.5 to 10 centimetres (0.20 to 3.94 in) in size. One end of the body is always firmly fixed to rock, coral, or some similar solid surface. The lower surface is pitted or ridged, and in some species has root-like extensions that help the animal grip onto the surface. The body wall is covered by a smooth thick tunic, which is often quite rigid. The tunic consists of a cellulose-like substance called tunicin along with proteins and calcium salts. Unlike the shells of molluscs, the tunic is composed of living tissue, and often has its own blood supply. In some colonial species, the tunics of adjacent individuals are fused into a single structure.
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