Opisthobranch of the Week Data
Petalifera ramosa is considered to be very rare on Okinawa as I have seen and collected only the single featured animal illustrated above. This little anapsid was discovered later at home in a sorting bowl of material from a grab sample of miscellaneous thallophytes (browns, greens, and reds). It was impossible to ascertain which alga the animal was collected from, but in the sorting bowl it was found crawling upon a frond of the brown alga, Lobophora (variegata?). If I were to hazard a guess, I'd say it was probably found originally on this brown alga as they certainly blend in well together. On the same page as that of the above Lobophora, I've included several additional images of the same 19mm animal.
This attractive and very cryptic anapsid was originally described by Baba (1959) based on eight specimens collected during the years 1933, 1938, 1939 and 1953 from waters associated with mainland Japan (Tomioka, Amakusa & Misaki, Sagami Bay.) Incidentally, the size range of the animals described by Baba is 50~70mm and those featured on Bill Rudman's Sea Slug Forum (Rudman, 1999) would appear to be much larger then that of the single Okinawa-collected specimen. Ron Greer's beautiful images from New South Wales of Petalifera ramosa on the Sea Slug Forum show both a green and brown form of the animal; the brown form being very similar to the Okinawa specimen.
The other Petalifera found here is Petalifera petalifera, although the two animals are easily distinguished from each other.