Taxonomical characters for distinguishing Cerithium lividulum Risso, 1826, and C. renovatum Monterosato, 1884 (Gastropoda, Caenogastropoda, Cerithiidae)

Protoconch and colour pattern of the living animal are here shown to be good characters for distinguishing smaller Mediterranean Cerithium species, Cerithium lividulum Risso, 1826, and C. renovatum Monterosato, 1884. In particular, the protoconch is a very helpful tool for recognizing atypical morphs. The shape of the shell and early teleoconch sculpture and microsculpture are not sufficient: the former character is too variable within each species and sculpture is similar in the two species. Observation of spawn deposited and cultured in an aquarium shows that both species have a non-planktotrophic larval development. However, C. lividulum shows variation in morphology and organization of egg mass. Specimens from NW. Sicily deposited eleven cylindrical egg masses, each egg containing one embryo, and one sac-like egg mass, each egg frequently containing 4 to 6 embryos. We think that the latter egg mass should be considered a rarity (anomaly?) rather than a representative taxonomical variation of C. lividulum. As far as concerns the Eastern Mediterranean populations, we show that the small, almost pupoid, knobbed morph from the Aegean Sea should be considered C. renovatum, while the larger crenulated morph, known as C. syriacum Pallary, 1938, also living in SE. Sicily, is suggested to be conspecific with C. lividulum. A shell from the Pallary collection, in the Museum National d’Histoire Naturelle (Paris), is here designated as lectotype of C. syriacum. Also, some morphs from the Eastern Atlantic are to be considered as belonging to C. lividulum. Use of the protoconch was successfully applied to fossil morphs. We identified C. lividulum (with ribbed or knobbed morphs) from Lower Pleistocene and C. renovatum from late Middle Pleistocene deposits.