The marvellous and strange Tethys fimbria

Dear Dom,

If we didn't know it was real, it would be easy to think that Tethys had been invented by an author of science fiction.

Your photos show the greatly enlarged rhinophore sheaths and very small rhinophores very well. In most nudibranchs, the rhinophores are vitally important as the organs of 'smell' which sense the chemicals in the water which will lead the nudibranch to its food. In Tethys, the sense of touch has replaced the sense of smell in the search for food, as can be seen by the development of the huge oral hood, with sensitive papillae around the edge, which search the substrate for the small crustacea that Tethys feeds on. In most nudibranchs, the rhinophores are relatively large and often quite elaborate, but in Tethys, where they apparently are no longer required in the search for food, they are very reduced in size.

A similar reduction in rhinophore size is found in species of the related genus Melibe.

Best wishes,
Bill Rudman