Opisthobranch of the Week Data
Chromodoris sinensis is considered to be uncommon on Okinawa. The species was previously known from Hong Kong (Rudman, 1985), but more recently Rudman (1990, 2000) points out it is also known from Japan, Singapore and Queensland, Australia. Ten Okinawan specimens have been collected and one other uncollected animal was photographed. The above featured animal was found while on snorkel during a minus spring tide in the late afternoon. It was found crawling on the surface of a patch of open sand, in an area composed of mixed sand, live stony corals, coral rubble, and patches of turtle grass (Thalassia sp.).
In the Sea Slug Forum (2000) Rudman characterizes the species as follows:
White with red outer and yellow inner mantle border. The white mantle is a translucent rather than an opaque white and in about half the specimens studied there can be scattering of small irregularly shaped red specks. The gills and rhinophore clubs are translucent red, and the rhinophore stalks are white, sometimes speckle[d] with red. It grows to approximately 30 mm in length.
This species has been recorded from Japan and China by various authors but misidentified with Chromodoris marginata (Pease), which is synonymous with C. verrieri. In Chromodoris verrieri the mantle is pigmented white whereas in C. sinensis the mantle is translucent white. In C. verrieri the gills and rhinophores are translucent and edged with white whereas in C. sinensis they are a translucent red. Most importantly the red outer colour band on the mantle is right at the edge in C. verrieri while in C. sinensis it is submarginal, there being a distinct,if narrow, marginal band of translucent white. From the many specimens available from Hong Kong it would appear that the presence of small orange-brown spots is variable, with approximately half the specimens so far collected having them.
C. sinensis is also similar in colour to C. preciosa and C. trimarginata. Both have a white outer band, then a red and then a yellow inner band to the mantle. In both cases the white outer band is of similar width to the yellow and red bands, while in C. sinensis the white band is much narrower and is translucent white rather than pigmented. In C. preciosa the rhinophore clubs and gills are translucent red with white edgings, and in C. trimarginata they are translucent clear with white edging.
In reference to one of the two animals mentioned in the Sea Slug Forum citation above, C. trimarginata is at this date (28 March, 2005) unknown from the waters of Okinawa's main island. C. sinensis is however similar to another more commonly found chromodorid here, Chromodoris preciosa, but the translucent white of the mantle seems to separate the two externally (the Okinawan specimens of C. preciosa seem to have a consistently darker central dorsum with numerous small darker spots of pigment).