Re: Radula of Senegalese Okenia zoobotryon [3]

Dear Marina,
Thanks for these photos. They do seem to show the 'hump' we were talking about, which is a bit of a problem, because I thought from your other photos that you had the 'humpless' animal. The 'hump' is right over the heart and pericardial cavity, so perhaps the variation is the result of some swelling in the pericardium - perhaps through salinity changes? If so, we could be looking at some temporary physiological change rather than a genetic species-level morphological difference. One way to check this would be to collect a few specimens and keep them in a container for a few days and see if they develop or lose a swelling in front of the gills. Adding a little freshwater to the container would certainly be one way of changing  the physiological conditions. Mind you, it would involve another trip to Senegal.

I am glad you enjoy these discussions. They are a good way of showing how we attempt to solve problems, and why taxonomists are usually cautious in naming 'new species' even when it seems blindingly obvious. The first step is to try and make sure the species has not been named before - and unfortunately that can sometimes be quite difficult, because in earlier times, new species descriptions were often very short of detail. The second major problem is deciding whether the animal you are looking at is indeed a new species or whether it is just a variation of an existing one. In this case we have a couple of names to use, but we can't be sure if we have two species or one.

Best wishes,
Bill Rudman