Small cryptic nudibranch. Body slender, slug-like, as high as broad, somewhat arched near the branchial region. Rhinophores smooth, not laminated and not retractile, without sheaths. Three bipinnate gills, situated in the middle of the back. Dorsal surface with small knobs or papillae, and one pair of longer, finger-shaped appendages behind the gills. Anterior edge of the foot with very short tentaculate corners; tail pointed.
cryptic coloration. General body color translucent yellowish, sprinkled with small dark brown dots on the back, upper sides of foot and tail, and with minute opaque white or yellowish-green spots on rhinophores, gills, back, upper sides of foot and tail.
common size :
up to 5 mm.
It is the sole species of Polycerella inhabiting the Atlantic and Mediterranean and it can be easily differentiated from any other nudibranch of the Mediterranean. Its small size, cryptic coloration, smooth and non retractile rhinophores, three naked gills and two extra-branchial appendages, situated postero-laterally to the branchial plume, are the distinguishing features of this species.
BIOLOGY / ECOLOGY
Feeds on the bryozoan Zoobotryon verticillatum in the eastern Atlantic basin and Mediterranean. In the western Atlantic it has been recorded feeding on the bryozoan Bowerbankia gracilis (Clark, 1975). Egg masses are produced at a very small size (3 mm long), and they are a short, strap-like cylinder with white eggs packed in different layers. Each egg mass contains no more than 100 eggs. Free-swimming veligers hatch after 11 days at 15° C (Schmekel and Portmann, 1982).
under rocks, in crevices and walls 1-2 m deep, where colonies of the bryozoan Zoobotryon verticillatum are present. In the western Atlantic it is a common species in fouling communities (Clark, 1975).