Aeolidia papillosa
Aeolidia papillosa, known as the common grey sea slug, is a species of nudibranch in the family Aeolidiidae.
Distribution
This nudibranch species thrives in cold-temperate waters in the Northern Hemisphere on the Atlantic coast of The British Isles and Northern Europe, the Atlantic coast of North America, and the north Pacific Coast of North America. This species has recently been shown to have a more restricted distribution than previously thought, with animals from California, France and Chile being three other species.Description
Aeolidia papillosa can be easily identified by its large number of cylindrical cerata covering its body except for a triangular area that extends from the rhinophores to the mid dorsum. The color is variable, usually with speckled darker markings in the head and back regions. To distinguish from different Aeolidia, A. papillosa has a distinct "V"- shaped pattern on the head of the animal that extends from one oral tentacle to its opposing pair tentacle. Adult A. papillosa reach up to 120 mm in length.Anatomy
In the order of Nudibranchia, these 'sea slugs' are not considered marine worms but instead mollusks who lack a shell which is a main characteristic in classification. Nudibranchia exhibit bilateral symmetry in overall body structure as well as in gill feature.Orientation and outer body plan
Since they lack an outer shell, Nudibranchia exhibit a specialized epithelium that protects them from predation and attacks from prey. Located in the epithelium are several vacuoles that aid them in secretions. The outside of the body is also covered with several cerata that have numerous functions. This feature, from the Greek word "κέρας" means "horn", is often associated with the suborder aeolid nudibranch. These protrusions are filled with blood and cover the animal laterally and dorsally. Inside each ceras, there is a duct that connects to the digestive system as well as a sac called cnidosac that holds defensive stinging nematocysts it acquires from eating its prey cnidaria. The pigments of cerata are dependent on the color of the digestive gland which can change by diet in translucent species.Internal organs and processes
Unlike other Aeolidida, the family Aeolidiidae possesses radular teeth which aid in feeding on their prey. The radula is a feature in majority of mollusks located in the mouth, like a tongue, containing thousands of teeth that help cut up food for digestion by scraping against rocks or evendrilling holes in prey in some species. This order is also classified by solid or circular columns of sensory tissues in the form of tentacles called rhinophores. In several groups of Nudibranchia, eyes can be located toward the bottom of these rhinophores which can entail possible homology of related ancestors. In internal organs, developing from the stomach is the intestine composing of a thick fold of tissue termed typhlosole which is plesiomorphic to Nudibranchia. In the superfamily Aeolidioidea, the typhlosole is present. The function of the typhlosole has not been determined, in some clades, it is possible that it aids in a secretion to help excretion of wastes or provides support in digestion of hard structures like sponge spicules.