Distinct protoconchs recognised in three of the larger Mediterranean <i>Cerithium</i> species (Caenogastropoda: Cerithiidae)

The gastropod genus <i>Cerithium</i> includes several polymorphic species which are hardly distinguishable using a morphological approach based on teleoconch characters. Here we show that protoconch characters can be reliably used to identify the larger Mediterranean species (<i>Cerithium alucastrum</i>, <i>C. repandum</i> and <i>C. vulgatum</i>), and to assess their intraspecific variability. Based on a large amount of morphological data, we show that a multispiral, strongly sculptured protoconch (traditionally associated with <i>C. vulgatum</i>) is found in <i>C. alucastrum</i>. This species originated in the Pliocene. A multispiral, weakly sculptured protoconch, not observed previously, is reported for <i>C. vulgatum</i>. A paucispiral protoconch, distinct from those observed previously for <i>C. lividulum</i> and <i>C. renovatum</i>, is reported for <i>C. repandum</i> and can be used for recognising its wide intraspecific variation and understanding its geographical distribution. <i>Cerithium repandum</i>, previously doubtfully recorded outside its type locality, extends back to the mid-Pliocene and is today rather widely distributed in the Mediterranean, although absent from the Aegean Sea and the Alboran Sea. We describe the larval development of <i>C. repandum</i> and <i>C. vulgatum</i> for the first time, confirming their respective non-planktotrophic and planktotrophic development previously inferred from protoconch morphology. Also, we report a possible case of morphological convergence between <i>C. repandum</i> and <i>C. vulgatum</i> occurring in harbour sites, where we found a distinct (possibly Anthropocene) shell form not described previously from other Recent or fossil material.