Hypselodoris zebrina - unseen for 150 years

Dear Priscilla,
This is an interesting find. I am sure it is Hypselodoris zebrina, a species which was described about 150 years ago from southeastern India and has never been reported since. I have scanned a copy of the original illustration alongside for comparison (Alder & Hancock, 1864: Plate 29, fig 7).

In the original description the colour of the stripes and the gills and rhinophores are described as 'crimson' but the illustration would suggest 'purple' may have been a better word to use. In your photo, the inner end of at least one of the purple lines is reddish. This shift from red to purple is not unusual in chromodorids, and would fit the juvenile nature of Alder & Hancock's small animal ('2 tenths of an inch long'). The yellow spots, radial purple lines, and purple dorso-median line down the posterior foot are all very characteristic features found in no other species of chromodorid.

It has similarities to Hypselodoris kanga, Hypselodoris nigrostriata and Hypselodoris zephyra all with yellow spots, and bluish purple lines, but in those species the gills are triangular in cross-section, while in your animal they are simple.

I am very glad you sent this photo even though it is not a perfect shot. It is an extremely valuable observation. I hope this will be a lesson for others who have less than perfect shots. This is primarily a slug site not a photo gallery so a less than perfect shot of an interesting animal or interesting behaviour is just as welcome as a perfect shot of a more common species.
Best wishes,
Bill Rudman