Shag-Rug Nudibranch

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.

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.

The family Aeolidiidae, as well as other Nudibranchia families, are often studied for their adaptable defense from the stinging nematocyst discharge of Cnidarian sea anemones in particular Actinia, Anemonia, Metridium, Sagartia and Urticina. Other food sources compose of zooxanthellae dinoflagellates which live in mutualistic relationship within the Nudibranch that provide nutrition in the tissues through photosynthesis. A. papillosa participate in "ingestive conditioning" in which they consume the nematocyst from their prey in response for predators in the same environment.

In the order of Nudibranchia, all experience a hermaphroditic nature with complete male and female reproductive organs. For A. papillosa, self-fertilization is rare and predominantly reproduces by means of copulation.