Small Translucent Nudibranch: Ardeadoris angustolutea

Ardeadoris angustolutea on a purple sponge, showing gills at lower left and rhinophores at upper right.

Ardeadoris angustolutea are widespread in the Indo-Pacific, ranging from the Marshall Islands to Thailand, and Australia to Japan. Sometimes they are called the yellow-margin dorid, but this one seems to have a white margin. I'll call it a small translucent nudibranch. This one is strolling across the surface of a purple sponge, as was the first one described; it's a good guess that they eat purple sponges (but maybe not exclusively).

Ardeadoris angustolutea on a purple sponge