Consider what this animal has to do to eat. A sea anemone is a column of muscle whose entire surface is loaded with stinging capsules that fire on contact, and the aeolidiids feed by climbing onto one and staying there, chewing into the column while the anemone does everything it can to the animal on top of it.
They get away with it because of what happens to the capsules afterward. The stinging cells are swallowed whole and unfired, carried through the gut without being triggered, and pushed out into sacs at the tips of the cerata on the slug's back. The anemone's weapons become the slug's weapons, and the slug goes back for more. Aeolids across the group do this with hydroids and corals; the aeolidiids are the branch that took on the biggest and best armed target available.
This is one of the larger ones, seven centimeters (2.8 in), and it is shaped for the job rather than for climbing. The body is broad, the foot is broad, and the back is packed edge to edge with short flattened cerata marked yellowish near their tips, so the animal reads as a bristling pad rather than as the delicate, finger-fringed thing most people picture when they hear aeolid.
Search for it the way you would search for its food. Anemones on sand and rubble flats are conspicuous and stationary; a large gray-brown slug sitting on one, at night, is not.
- large for an aeolid, with the back completely covered in short flattened cerata
- cerata carrying yellowish markings near the tips
- broad body and broad foot, built to sit on a surface rather than climb a branch
- found on or beside an anemone, and often only after the anemone is noticed
