Roboastra luteolineata vs Tambja verconis

Dear Ross & Diane,
What a wonderful find - though a bit sad for the Tambja. It is certainly convincing support for my view that the striped animal is a species of the nudibranch-hunting genus Roboastra rather than the bryozoan-feeding genus Tambja. Actually in your upper photo we can see the whole food chain, for at the bottom left I can see some small branches of the bluish arborescent bryozoan Bugula dentata on which Tambja verconis feeds.

Although we call the mollusc radula their 'teeth' they work in quite a different way to vertebrate teeth. A carnivorous vertebrate like a dog or a lion woud use its teeth to bite off or tear off chunks of flesh and swallow them. The mollusc radula can perhaps be compared with having teeth on our tongue. Although they can be manipulated in ingenious ways, molluscs have never evolved a way to use the radula to bite of large chunks. In carnivorous hunters the teeth have become a set of grappling hooks which can grab and hold on to their prey while the the 'oral tube' which is a very extensible region just inside the mouth, extends out of the mouth by turning inside out, and wraps itself around the prey. Once it has done this it can then pull itself and the prey back into its body for digestion.

I think this is the first record of anyhting feeding on Tambja verconis and I don't know of any observations of Roboastra luteolineata feeding in Australia or NZ. Atsushi Ono has a couple of photos of it in his book feeding on another species of Tambja in Japan.

Thanks again for sharing this very interesting observation.
Best wishes,
Bill Rudman