Re: Hypselodoris bennetti & Ceratosoma amoena

Dear Leanne & David,
Thanks for this record - though I am not sure what it is a record of. In Lynda's earlier message the Hypselodoris seems to have its oral tube out, suggesting that it is feeding on the Psammocinia but I don't know whether the Ceratosoma is just 'watching' or eating as well. I think the sponge in your message here is a species of Semitaspongia which is a genus of sponges we often find Ceratosoma amoena feeding on but until now the only feeding records for H. bennetti have been from Psammocinia. So the question here must be is H. bennetti just 'watching'.

Hypselodoris bennetti is a bit of a puzzle because most species of Hyspelodoris feed on sponges of the Dysideidae, while it alone feeds on a species in the Irciniidae. Interestingly, Semitaspongia is in the family Thorectidae and there is one Mediterranean Hypselodoris which feeds on a thorectid, so if H. bennetti also eats Semitaspongia it wouldn't be totally outrageous. I mention all this, not because I want to confuse you, but to show that accurately finding the prey of each species is giving us an interesting insight into relationships.

High resolution photos like this which allow us to see sponge structure are very valuable. It is also useful to include a photo of the sponge colony. But as you note, we need a positive feeding shot, to resolve puzzles like this. Some people have asked me what about studying stomach contents? The problems with chromodorids is that they feed on groups of sponges which lack mineral spicules in their skeletons so there is nothing in the stomach contents to identify. You can certainly find some sponge spicules in chromodorid stomachs from a vast variety of sponge families but that is because the sea floor is littered with stray sponge spicules which are ingested as an animal feeds on its chosen food. Even herbivores have been reported to eat sponges when the presence of such spicules in stomach contents are misinterpreted.

Best wishes,
Bill Rudman