Opisthobranch of the Week Data
Thecacera pennigera is a widespread species, and is found in Australia, Brazil, New Zealand, Okinawa, Pakistan, South Africa, Japan, as well as numerous European sites. The species is known to feed upon arborescent bryozoans (e.g., Bugula spp.), as the photo above illustrates. Willan (1976) mentions that perhaps the widespread distribution of T. pennigera is a result of its being transported on ship's hulls. Gosliner (1987) reports, however, that in South Africa, specimens have been found several hundred kilometers from the nearest harbor.
Thecacera pennigera is considered to be very rare on Okinawa as I have only seen and collected a single specimen. This very attractive little polycerid has a pair of large prominent glandular processes, located posterior to the gills, which are apparently used as a defensive mechanism in deterring predators. Although there are two other species of Thecacera with comparable appearing glandular processes found here, T. pacifica and T. picta, the distinctive color patterns of all three animals serves to separate them from one another.