IS CYPRIDEIS AGRIGENTINA DECIMA A GOOD PALAEOSALINOMETER FOR THE MESSINIAN SALINITY CRISIS? MORPHOMETRICAL AND GEOCHEMICAL ANALYSES FROM THE ERACLEA MINOA SECTION (SICILY)

Since the study of VESPER (1975) and ROSENFELD & VESPER (1977), it is known that the living anomalohaline species Cyprideis torosa (Jones) undergoes morphometrical variations in size, noding and sieve pore shape linked to the environmental salinity. Several studies (among others: CARBONEL, 1982; ALADIN, 1993; VAN HARTEN, 1996; KEYSER, 2005; BOOMER & FRENZEL, 2011; FRENZEL et al., 2011, 2012) showed that salinity values around 8-9 psu represent the osmoregulation threshold and also the turning point between smaller and greater valve dimensions and prevailingly noded against un-noded valves. The variation of the percentage of round-, elongate- and irregularshaped sieve pores on the valves has shown an empiric logarithmic correlation with the water salinity from 0 to 100 psu (ROSENFELD & VESPER, 1977). Due to this ecologically cued polymorphism, Cyprideis torosa represents an invaluable palaeosalinometer for Quaternary brackish basins. Some authors (ROSENFELD, 1977; BONADUCE & SGARRELLA, 1999) applied the counting of different sieve pore shapes also to the fossil species Cyprideis agrigentina Decima, distributed in the Mediterranean during the post-evaporitic Messinian lago-mare phase. In this paper we attempt to verify whether the ecophenotypical behaviour of C. agrigentina was comparable with that of C. torosa.