Chelonibia testudinaria
Chelonibia testudinaria is a species of barnacle in the family Chelonibiidae. It is native to the Atlantic Ocean, Mediterranean Sea and Gulf of Mexico where it lives as a symbiont on sea turtles, being particularly abundant on the loggerhead sea turtle ("Caretta caretta"). Taxonomy. Historically, the genus "Chelonibia" contained "C. testudinaria", found growing only on sea turtles, and "C. patula", a generalist found growing on a range of living hosts including decapods, gastropods, mantis shrimps and sea snakes, but very rarely on sea turtles. It was puzzling why a barnacle that was adaptable to such a broad range  of hosts, should avoid the sea turtle. The two are distinguished morphologically as well as by host, and were thought to be different species. However, examination of the genetic differences between the pair showed that they are in fact con-specific. Description. "C. patula" has a conical shaped shell with smooth plates, with long cirri IV, V and VI. Dwarf males often settle on the plates and are distributed randomly. In contrast, "C. testudinaria" has a flatter, less conical shape, the cirri IV, V and VI are short, and there are shallow oval depressions on the radii at the junctions  of the plates. Dwarf males commonly settle in these depressions. Size, Growth and Age. The growth rate of "C. testudinaria" follows a non-linear growth pattern where rate of increase in length slows with age. Applying a von Bertalanffy growth model to the population suggests that the maximum achievable size of "C. testudinaria" on loggerhead turtles in the wild is approximately 70 mm in rostro-carinal length. The largest individuals reported to date indicate that this species can live for at least 21 months. However, mortality is (at least partially) controlled by the scute sloughing frequency of host turtles, meaning  that barnacles on living on hosts which shed less frequently, or not at all, may live longer. Ecology. "C. testudinaria" preferentially behaviorally select green turtles as hosts compared to "Chelonibia caretta", which select Hawksbill sea turtles as hosts. On a turtle's shell, the greatest water flow is over the front central portion. It has been shown that "C. testudinaria" can relocate on the turtle's shell, usually towards the optimal position with maximum water flow and thus the greatest filter feeding opportunities. The movement is around or less per day and is probably achieved by advancing the shell forward  with each increment of growth. Over several months, several scutes can be crossed by these means.