Mystery from Malaysian Borneo

Dear Sean,
This is a species of Trapania, which I am calling Trapania cf brunnea because I am not sure if it is different from Trapania brunnea or not. In your photos it is crawling over a sponge, which is where species of Trapania are often found. Despite your apologies, the photos are excellent. Although the sponge may look out of focus, it is in fact covered with a plant-like growth which is a colony of microscopic animals called kamptozoa on which it feeds. In your upper photo the finger-like feeding tentacles of the kamptozoan zooids can be seen along the top edge of the sponge, and at the bottom of the photo you can see small brown spots, which are the intestinal remains in the gut of each animal. Your photos have enabled me to finish a Fact Sheet on the Kamptozoa. For comparison I have also prepared one on the Bryozoa, another food item of some nudibranchs. Both the Kamptozoa and the Bryozoa were once thought to be closely related.

If you look at other species of Trapania on the Forum, you will see that like your animal, they all have a curved appendage attached to the outer base of each rhinophore stalk.

Best wishes,
Bill Rudman