Labellicula lecohuiana, a new epizoic diatom species living on green turtles in Costa Rica.

It has been known for a long time that marine mammals, such as whales and dolphins, host a very specific epizoic community on their skin. Whether or not a similar community exists on the carapaces of sea turtles is less studied. The present paper describes two new epizoic diatoms from the genus Achnanthes sensu stricto found on the carapace of nesting olive ridley sea turtles (Lepidochelys olivacea) in Ostional Beach on the Pacific coast of Costa Rica, based upon detailed scanning electron microscopy and comparison with the type material of A. groenlandica var. phinneyi and A. pseudogroenlandica. The two taxa, A. elongata and A. squaliformis, appear to be closely related on the basis of their morphological features including long, slender valves, absence of terminal orbiculi, large cribrate areolae and absence of typical costae on the internal virgae of both valves. They can, however, be differentiated from each other by the number of areolae per stria, the position of the rapheless sternum, and differences in their length/width ratio.

A new Labellicula species, L. lecohuiana Majewska & Van de Vijver sp. nov., was observed living epizoically on the carapaces of green sea turtles in Costa Rican coastal waters. The new species, showing a narrowly lanceolate valve outline, is characterized by uniseriate striae composed of one large macroareola, a rather simple raphe structure with hooked terminal raphe fissures, the presence of two globular structures in the valve interior covering the isolated pore and a cingulum composed of several open, doubly perforated copulae. The new taxon can be distinguished from the only other Labellicula species known to date, the sub-Antarctic L. subantarctica, by differences in raphe structure and valve outline. Labellicula lecohuiana lacks both the distinct bucinoportula and the marginal canal typical of the genus Olifantiella and thus, the latter is excluded as the host genus for the new taxon.