Blue Dorid

Hypselodoris festiva

Hypselodoris festiva is a strikingly beautiful nudibranch reaching about 5 cm in length, found primarily in the western Pacific from Japan to the Philippines. Its mantle is a vivid blue to purple-blue, decorated with yellow to orange-gold lines and spots that create an intricate pattern unique to each individual. The mantle margin is often edged with a thin yellow-orange line, and the rhinophores and gills are deep purple to blue. This species belongs to the chromodorid family, whose members are renowned for their spectacular colors, which serve as aposematic warning signals to predators. The bright coloration advertises the presence of distasteful chemical compounds derived from the sponges on which it feeds. Hypselodoris festiva is typically found on rocky reefs and coral rubble where its preferred sponge prey grows, at depths from the shallows to about 30 meters. It is especially popular among underwater photographers in Japan, where it is commonly encountered at diving hotspots like Izu, Kushimoto, and Okinawa. Like all nudibranchs, it is a hermaphrodite that lays spiral-shaped egg ribbons on the substrate.