More on Tyrinna nobilis from Tristan da Cunha

Dear Sue,

Thanks for these photos.  I can't wait for your next visit. perhaps you will find Tyrinna on its food sponge. At present I suspect it feeds on a dysideid sponge because natural products chemists have isolated a sesquiterpene molecule from its mantle tissue, a molecule usually found in dysideid sponges.

While we can't be sure of the origin of the egg ribbons, they certainly fit the published description and drawing (Muniain et al, 1996) of its egg ribbon except for one feature - the direction of spiral. In the days of film cameras, photos were often reversed in various copying and printing processes and usually only noticed by people familar with the direction of shell and egg ribbon spirals. I am not sure if you used a film camera or a digital camera or if Muniain et al did. It is also possible that both of you have recorded the spirality correctly and this isn't the egg ribbon of Tyrinna nobilis.

Any clues or corrections welcome

• Muniain, C., A. Valdés, et al. (1996). Redescription of Tyrinna nobilis Bergh,1898 (Opisthobranchia: Chromodorididae) from Patagonia, Argentina. Journal of Molluscan Studies 62: 265-273.

Best wishes,
Bill Rudman