A new sponge-mimicking Ceratosoma

Dear Harald,

These are both species of the chromodorid genus Ceratosoma. The orange-spotted animal is a colour form of Ceratosoma trilobatum, but the pale purple one is an unnamed species which is apparently mimicking the sponge it feeds on. I must warn you that this is a big guess on my part because we don't know what your animal feeds on and we have little information on what many species of Ceratosoma feed on. However all species of Ceratosoma for which we have some information feed on sponges of the family Dysideidae, and if you have a look at a few examples of dysideid sponges on the Forum [see messages #2826, #11334, #19789] you will see it does indeed have a remarkable resemblance to such a sponge. I am sure the pale network in the skin is not a network of muscle fibres but a colour pattern to match the spongin fibres found in the fibrous skeleton of dysideid sponges..

I guess it is surprising just how few chromodorids have used camouflage as part of their defensive strategy. The best example is Verconia verconis, which mimics the darwinellid sponges it feeds on, but I suspect this Ceratosoma will turn out to be just as good a mimic - once we find it on its food. I will call it Ceratosoma sp. 2.

Best wishes,
Bill Rudman