Coloring is often black or a very dark brown, sometimes with a thin red border to the parapodia, foot, and tentacles.

Aplysia fasciata have, like most sea slugs, two oral tentacles and two more smaller rhinopores in front on their neck.

Aplysia fasciata eat algae and seaweed attached to rocks and other surfaces.

The ink takes on a purple hue, a result of eating red algae.

It is believed to be non-toxic, though is assumed that the ink is secreted as a result of a sort of physical "assault" on the sea hare.