Relevant Synonyms Polycerella recondita [Schmekel, 1965] Misidentification -  drawing: Tuvia Kurz

SHORT DESCRIPTION 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. color : 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. DISTINGUISHING CHARACTERISTICS 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). habitat : 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).

1st Mediterranean record Italy, 1965 [1964]. DISTRIBUTION Worldwide: warm-temperate amphiatlantic species (Eyster, 1980); common from Massachusetts to Brazil, in the eastern Atlantic, recorded in Ghana (Edmunds, 1977, as Polycerella sp.), and from El Portil, SW Atlantic coast of Spain (Garcia and Bobo, 1986). Mediterranean: recorded first in 1964 from Lago Fusaro (Schmekel, 1965); successively from Toscany coasts (Cattaneo-Vietti et al., 1990); Malta (Sammut and Perrone, 1998) and Greece (Koutsoubas et al., 2000). ESTABLISHMENT SUCCESS Widespread but rare. speculated reasons for success : - MODE OF INTRODUCTION This species probably crossed the Atlantic water on boat hulls. IMPORTANCE TO HUMANS None.

KEY REFERENCES Franz D.R. and Clarck K.B., 1972. A discussion of the systematics, reproductive biology and zoogeography of Polycerella emertoni and related species (Gastropoda: Nudibranchia). The Veliger, 14: 265-268. Garcia J.C. and Bobo A., 1986. Un nuevo Doridaceo para el litoral Iberico: Polycerella emertoni Verrill (1880) 1881 (Gastropoda: Nudibranchia). Bollettino Malacologico, 22(1-4): 49-56. Schmekel L., 1965. Die gattung Polycerella Verrill im Mittelmeer (Gastrp. Opisthobranchia). Pubblicazione della Satazione Zoologica di Napoli, 34: 226-234.   Schmekel L. and Portmann A., 1982. Opisthobranchia des Mittelmeeres. Springer, Berlin, 410 p. FEEDBACK / COMMENTS TO AUTHORS

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