Roboastra luteolineata - Feeding behaviour!

Dear Graham,
Thanks for the interesting sequence of photos. The fortunate 'prey' animal is very similar to a photo I have identified as Tambja tentaculata [message #14883]. We don't know much about that recently named species, but if it is like other species of Tambja, it will feed on bryozoans. Chromodoris willani is quite different in shape and colour, and is a sponge feeder.

Nudibranchs of the genus Roboastra are well-known as hunters, but it seems they restrict their prey to other nudibranchs of the family Polyceridae. They certainly seem to eat smaller members of their own species, so I guess you can call them cannibals, but they are not exclusively cannibals. The two species most studied are the tropical American R. tigris which feeds on Tambja abdere and T. eliora, and the European R. europaea, which feeds on a variety of polycerids (Megina & Cervera, 2003). From work on R. tigris, we know that distasteful chemicals are incorporated in tissues of the bryozoan-feeding species of Tambja, and then transferred to the Roboastra, when it eats them (Carte & Faulkner, 1986). I presume something similar could happen with Tambja tentaculata and R. luteolineata, but I doubt it would lead to the Roboastra rejecting the Tambja. It is possible the Roboastra was just being greedy. These hunters seem to attack by reflex action whenever they come across prey. Perhaps it discovered it didn't really have room inside once it started swallowing.

• Carte, B. & Faulkner, D.J. (1986)  Role of secondary metabolites in feeding associations between a predatory nudibranch, two grazing nudibranchs, and a bryozoan. Journal of Chemical Ecology, 12(3): 795-804.
• Megina, C. and Cervera, J. L. (2003) Diet, prey selection, and cannibalism in the hunter opisthobranch Roboastra europaea. Journal of the marine biological Association, U.K. 83: 489-495.

Best wishes,
Bill Rudman