Ascidiacea is a class in the Tunicata subphylum 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.
1. a part of the circumference of a circle or other curve.
2. a luminous electrical discharge between two electrodes or other points.
3.(in a novel, play, or movie) the development or resolution of the narrative or principal theme.