Morphobiometry of the scleral ossicle rings in Chelonia mydas sea turtles

Scleral ossicle rings of reptiles have endoskeletal functions that are not completely understood. Moreover, descriptive reports on the anatomy of those rings are scarce. We tried to make an anatomical description that could contribute to a better understanding of their functions.

We quantified, histologically characterized and evaluated the morphobiometry of the scleral ossicles, and measured the aditus orbitae of 25 sea turtle (Chelonia mydas) heads.

The aditus orbitae represented about one-third of the total head length and the mean area of the internal opening of each ring was up to 8.37% of the aditus orbitae area. The mean internal diameter of the rings (6.32 mm) was characteristic of scotopic species and the most frequent number of ossicles per ring varied between 11 and 12. Two new classifications were proposed for the ossicle types: plus-Verzahnung (+V) and minus-Verzahnung (-V). The bone tissue revealed a lamellar arrangement typical of compact and resistant bones.

The obtained data may be used to support and expand the understanding of functions, animal activity patterns, distinctions between taxa and taphonomic interpretations.