Notodoris minor - feeding behaviour

Dear Mary Jane,
I am pretty sure this is the calcareous sponge Pericharax heteroraphis which is the only sponge I have records of N. minor and N. gardineri feeding on.

The pile of spicules alongside the feeding animal is also quite characteristic. These spicules are part of the skeletal framework which hold the sponge together. What we don't know is how it separates out the spicules while it is eating. Most sponge-feeders eat their sponge in chunks spicules and all, sorting out the spicules in their stomach and passing them in their faeces. This doesn't seem to be the case here. There seem to be three possibilities.
• 1. The nudibranch spits the spicules out as its feeding (like I eat bony fish).
• 2. It somehow predigests the sponge, perhaps with salivary juices, and sucks up the digested tissue leaving the spicules behind.
• 3. It eats all the sponge and somehow passes the spicules through its digestive system. (not very likely as the spicules are clean and separate).

If anyone wants to stop and watch Notodoris feeding for an hour or so, it would be interesting to know how these piles of clean spicules are formed.

Finally about the identity of Notodoris's food. I read today in Gosliner, T.M., Behrens, D.W. & Williams, G.C. (1996) [Coral Reef Animals of the Indo Pacific: Sea Challengers, Monterey, 314pp] that they state that N. minor & N. gardineri feed on the calcareous sponge Leucetta primigenia, which is red in colour with a white band bordering the the openings of its flask-like structure. I have no record, or have seen no photo, of these species on anything but the brownish sponge you illustrate above and I have had identified as Pericharax. Perhaps they feed on both sponges.

As I state elsewhere, N. citrina feeds on a bright yellow species of Leucetta.

Bill Rudman.