This species is a simple, solitary ascidian, with a thin outer covering or tunic. Overall shape is typically described as irregular or oblong; and although the body is longer than wide and measures 2-6 cm in length, this species attaches to the substrate along its side rather than its base, resulting in a compressed or flattened appearance. The tunic surface is covered with small bumps or finger-like projections (papillae); however in some individuals, these papillae may appear only around the siphons. Both the oral and atrial siphons are positioned in the anterior third of the body. Overall color varies from translucent to pale yellow or beige, but often the tunic is covered with other fouling organisms or debris. Eggs are red in color.
In the Northeast Pacific, Ascidia zara is most similar to other ascidiid tunicates, including A. ceratodes (Huntsman, 1912), A. columbiana (Huntsman, 1912), A. paratropa (Huntsman, 1912), and another non-native species documented from the region, Ascidia sp. Lambert & Lambert 1998.