The oldest platylepadid turtle barnacle (Cirripedia, Coronuloidea): a new species of Platylepas from the Lower Pleistocene of Italy

Abstract

Coronuloid barnacles are epibionts of several marine vertebrates (including cetaceans and sea turtles) as well as invertebrates, and are assigned to two families of turtle barnacles (Chelonibiidae Pilsbry, 1916 and Platylepadidae Newman & Ross, 1976) and one family of whale barnacles (Coronulidae Leach, 1817). Chelonibiids and coronulids have a scanty, albeit significant fossil record extending back to the Eocene and Pliocene, respectively; in turn, the fossil record of platylepadids is limited to a single record from the Upper Pleistocene. Here we report on an isolated carinolateral compartment of Platylepas Gray, 1825, the type genus of the family, from Lower Pleistocene (Gelasian) epibathyal deposits exposed at Milazzo (Sicily, Italy). This specimen is here designated holotype of a new species, †Platylepas mediterranea sp. nov. We argue that, like most extant members of Platylepas, †P. mediterranea sp. nov. lived partially embedded in the skin of a sea turtle. This record of an extinct platylepadid – the first from the Mediterranean region and the second worldwide – pushes back the fossil record of Platylepadidae to the lowermost Quaternary, thus possibly supporting an even earlier (e.g., Neogene) timing for the origin of this family and adding a new chapter to the evolutionary history of one of the most diverse and successful lineages of epizoic crustaceans.

New and overlooked occurrences of the rarely reported protochelonibiine “turtle” barnacles from the Oligocene and Miocene of Europe

“…The Oligo-Miocene species of Protochelonibia have low-conical shells, and consequently, they were likely specialised for spreading over the substrate in a way much similar to the living platylepadid species Platylepas coriacea Monroe & Limpus, 1979, whose shell is characteristically not embedded into the host's tissues (cf. discussion in Collareta et al 2019). A few compartments of P. melleni display a jagged basal profile (Zullo 1982;Collareta and Newman 2021) that is reminiscent of the invaginations and rib-like structures observed at the base of some shells of C. caretta and the manati morph of C. testudinaria (a manatee-fouling form; Pilsbry 1916), thus suggesting a certain degree of penetration into some kind of ductile tissue (Gruvel 1903;Monroe 1981); that said, most specimens of P. melleni exhibit a regularly rounded periphery (Zullo 1982: pl.…”

A new chelonibiid from the Miocene of Zanzibar (Eastern Africa) sheds light on the evolution of shell architecture in turtle and whale barnacles (Cirripedia: Coronuloidea)

“…zanzibarensis compares favorably with the overall aspect of specimens of Platylepas for which penetration into a soft substratum has been observed (e.g. Pilsbry 1916) or presumed (Collareta et al 2019). Indeed, as illustrated by the presence of a distinct substrate imprint on the shell exterior, ≈5 mm above the shell base (Fig.…”

“…Pilsbry 1916 ) or presumed (Collareta et al . 2019 ). Indeed, as illustrated by the presence of a distinct substrate imprint on the shell exterior, ≈5 mm above the shell base (Fig.…”

“…These striations define external parietal canals that were exposed by sub‐apical erosion of the shell and appear as partly filled by a blackish, possibly carbonaceous material, as well as by diagenetic cement. The external longitudinal parietal canals of NHMUK PI In.26663 are similar to (but distinctly larger than) those observed in various species of Platylepas Gray, 1825 —for example, Platylepas hexastylos (Fabricius, 1798 ) or † Platylepas mediterranea Collareta et al ., 2019 —and are divided from each other by external longitudinal parietal septa. On R, some septa are observed to bifurcate downwards due to the appearance of a new canal (Fig.…”

Turtle barnacles have been turtle riders for more than 30 million years

“…Compared to the fossil record of chelonibiids, that of platylepadids is extremely fragmentary and limited to a handful of occurrences of the extant genus Platylepas from Pleistocene deposits (Ross 1963;Mimoto 1991;Collareta et al 2019;Karasawa and Kobayashi 2022). According to Hayashi et al (2013), this sparse fossil record is likely due to the fragility and small size of the shell of Platylepas and allied genera.…”