The body is elongate oval, the mantlewhite or translucent white with white specks, but also greenish grey. The gills and rhinophores are white in colour. The bushy gills which are fully retractable into a pocket. OThe mantle is covered with large and small conical tubercles. Blue or brown digestive glands may be seen through the body.
Aldisa zetlandica can be found in sponge rich areas amongst a variety of Axinellid sponges.
Silimar to Cadlina laevis ,which is much flatter in profile. And small individuals could be confused with Adalaria or Onchidoris muricata ( have no true gill pocket).