Doriprismatica atromarginata is a species of sea slug. It lives commensally on a number of hosts, including the sea slug "Hexabranchus". Berghia stephanieae is a species of sea slug, an aeolid nudibranch. It is the largest sea slug species. The patterns and rate of these changes, however, varies between different species of sea slug. Berghia coerulescens is a species of sea slug, a marine nudibranch in the family Aeolidiidae. Its predator is the striped sea slug, "Armina tigrina". Facelina bostoniensis is a species of sea slug, an aeolid nudibranch in the family Facelinidae. Similarly in the sea slug "Glaucus atlanticus", the reverse countershading is associated with inverted habits. The medicinal leech, "Hirudo medicinalis," and sea slug are classic model systems for studying nociception. He described the sea slug species "Chelidonura varians" . The lettuce sea slug ("Elysia crispata") has lettuce-like ruffles that line its body. The Sea Slug system was retained, although only for use against surface targets. Pteraeolidia ianthina is a sea slug, an aeolid nudibranch in the family Facelinidae.