A new species of the archaic “turtle barnacle” genus Protochelonibia (Coronuloidea, Chelonibiidae) from the upper Rupelian Chickasawhay Formation of Mississippi (U.S.A.)

Protochelonibia starnesi sp. nov. (Coronuloidea, Chelonibiidae) is described herein from the upper Rupelian Chickasawhay Formation of Mississippi (U.S.A.). This new “turtle barnacle” species shares similarities with both the extinct Protochelonibia melleni (Zullo, 1982) and the extant Chelonibia “manati” Gruvel, 1903. Similar to the latter, P. starnesi possibly dwelt on sirenians, or the soft skin of other vertebrates. Both P. melleni (whose first representative from the Marianna Formation of Mississippi is also described herein) and P. starnesi attained large shell sizes. Together, they represent the oldest unambiguous members of Coronuloidea, as well as the oldest chelonibiid taxa. As the oldest putative coronuloid is also known from the U.S. Gulf Coast, the Eocene marine deposits exposed over this broad region are a strong candidate to preserve remains of transitional forms.