These sea squirts remind me of Faberge eggs or millefiore paperweights. This Haeckel plate of ascidiae on a black background is one of his most beautiful. Ascidiacea (commonly known as the ascidians or sea squirts) is a class in the Urochordata subphylum of sac-like marine invertebrate filter feeders. Ascidians are chraacterised by a tough outer "tunic" made of the polysaccharide tunicin. Ascidians are found all over the world, usually in shallow water. Sea squirts are sessile animals: they remain firmly attached to substratum such as rocks and shells.