First fossil record of early Sarmatian didemnid ascidian spicules (Tunicata) from Moldova

Numerous ascidian spicules are reported for the first time from the lower Sarmatian Darabani-Mitoc Clays of Costeşti, north-western Moldova. The biological interpretation of the studied sclerites allows distinguishing at least three morphospecies (Polysyncraton-like, Trididemnum-like, and Didemnum-like) within the Didemnidae family. Eight other morphological types of spicules are classified as indeterminate didemnids. Most of the studied spicules are morphologically similar to those of Recent shallow-water taxa from the Mediterranean Sea. In contrast, some sclerites resemble those of taxa from the Indo-Pacific region. The greater size of the studied spicules, compared to that of present-day didemnids, suggests favorable physicochemical conditions within the Sarmatian Sea. The presence of these stenohaline tunicates that prefer normal salinity seems to confirm latest hypotheses regarding mixo-mesohaline conditions during the early Sarmatian.