Hypselodoris festiva from Korea

Dear Dong Bum,
Baba (1995) discusses two colour forms of H. festiva but they revolve around the presence or absence of dark blue black spots, not the absence of yellow and orange pigmentation, as in your lower photo. However, considering how similar the general colour pattern is. I would think the most reasonable explanation is that the lower individual is an abnormal specimen in which the pigment which produces the orange and yellow markings is almost completely absent. A faint orange tinge on the rhinophores and gills would seem to support this idea. Of course a look at the anatomy might show differences but I suspect you would learn more by checking how abundant this pale colour form is, and whether it is feeding on the same sponge, and perhaps aggregating with more typical colour forms of H. festiva.

• Baba, K. (1995). Anatomical and taxonomical review of four blue-patterned species of Hypselodoris (Nudibranchia: Chromodorididae) from Japan. Venus (Japanese Journal of Malacology), 54(1): 1-15.

Best wishes,
Bill Rudman