Opisthobranch of the Week Data
Phyllidia varicosa is considered to be common on Okinawa; I should point out that I've only collected five specimens (as of November, 1999), however, many others have been seen but not collected.
Phyllidia varicosa is very similar to a closely related phyllidiid, P. coelestis. The easiest way to distinguish between the two similar animals in the field, e.g., while on SCUBA, is that P. varicosa has a longitudinal black stripe on the crawling surface of the foot (the black stripe is sometimes intermittent, or sometimes continuous as the preceding link illustrates), whereas P. coelestis is without the black stripe. Another superficially similar appearing phyllidiid found on Okinawa is P. elegans; much the same as P. varicosa, P. elegans also has a black stripe on the crawling surface of the foot, but in addition to the black foot stripe, there are also black lines on the sides of the foot as well. The distinctive pinkish color of the nodal tubercles also serve to segregate P. elegans (Brunckhorst, 1993) from the above featured animal. Brunckhorst (1993) lists additional external morphological characters useful in segregating the above three species.
In addition, I've added a link featuring a juvenile specimen of P. varicosa as well as a P. varicosa mimic.