Ascidians

(ās-sid'yans.) [From Gr. as kos, a wineskin.] (Zool.) An O. of acephalous mollusks (also called Tunic at a), which have no hard parts, but which are protected by an elastic tunic instead of a shell. Some are transparent, so that their whole internal structure may be easily seen. Ascidia rustic a, found in clusters adhering to stones and floating timbers in Boston harbor, is about the size of a pea. [s. 51]