Risbecia godeffroyana from Great Barrier Reef

Dear Andrew,

This is the chromodorid Risbecia godeffroyana. I have included a couple of close ups to show the detail in the colour pattern and the gills. The white ring in the centre of the gills is the tip of the anal papilla.

 As you can see, the gills in this species do not form a simple circle. Instead on each side they form an inwardly coiling spiral which greatly increases the number of gills. I have not collected diligent statistics on this but the species which form inward spirals like this are the larger species which have thicker, more muscular, body walls. In species with a thinner body wall I suspect the body wall acts as a secondary gill allowing some passage of gases. My hypothesis is that as the body wall thickens and can no longer act as a semipermeable membrane, the need to increase the number of gills becomes important. With the microprobes available today it might be an interesting little project for someone.

Best wishes,
Bill Rudman