Separated from the other opisthobranchs, the notaspideans are "side-gilled". Their gills are a series of unipinnate processes found along the right side of the body. The shell is external in of the genera. In the remaining species of notaspideans, the shell is internal (except for one which lacks one entirely), covered by the notum, and is transparent, fragile, and flat with a very wide aperture. The rhinophores are rolled. Members of this order are exclusively carnivorous and have strong jaws and a wide radula to scrape and feed upon tissue from their sponge and or tunicate prey.