This species is a simple, solitary ascidian. Overall shape is described as flattened and elongated with the body measuring up to 3 cm in width and 6 cm in length. The oral siphon is long and located anteriorly, whereas the atrial siphon is positioned in the posterior half of the body. The tunic is fairly transparent, and eggs (visible through the tunic) are clear to pale yellow in color. See Lambert & Lambert, 1998.
In the Northeast Pacific, Ascidia sp. is most similar to other ascidiid tunicates, including A. callosa Stimpson, 1852, A. ceratodes (Huntsman, 1912), A. columbiana (Huntsman, 1912), A. paratropa (Huntsman, 1912), A. prunum Müller, 1776, and another non-native species found in the region, A. zara Oka 1935.
Ascidia sp. has been found in central and southern California, but appears to be rather ephemeral (Lambert & Lambert 1998). This may be the same species as Ascidia sp. B, previously reported from Hawaii. Its native geographical range remains unknown.