Is there such a thing as a flat Nudi?

My wife and I have been swimming near an estuary lately and today while walking on the rocks past a tidepool we saw this flat "thing". It was about 4 inches long, 2.5 inches wide and moved very quickly over rock out of the water until it got back into a pool where it flattened itself into a crevice. Anyone know what it is?

A flatworm, so not a nudie but a different animal group. Probably best to wait for Leslie for an ID. Would help if you mentioned where it was seen.

Gerard

The photo was taken in the East China Sea.

Gerard's right, it's a polyclad flatworm. In general nudibranchs have some depth to their bodies and move slowly. Flatworms are flat although there may be a lump along the midline if they've recently feed or are reproductive and move quickly. Some species have unique color patterns and are easy to identify. Some color patterns - like this spotted one - occur in several species so they're useless for id. Classification of these guys is based on internal structures like details of the digestive & reproductive systems. Two good/reliable web sites for picture id are Marian Litvaitis" Discover Life at http://pick5.pick.uga.edu/mp/20p?see=I_ML/0000 and Wolfgang Seifarth's Marine Flatworms of the World http://www.rzuser.uni-heidelberg.de/~bu6/index.html

Thank you for the reply! It was very interesting watching the flatworm make his way across the tidal pool to get to the water. It was sort of a flipping/rolling action and this is what caught our attention. Once it got into the pool it virtually disappeared into a small crevice by folding in on itself.