Two new epizoic Achnanthes species (Bacillariophyta) living on marine turtles from Costa Rica

Abstract

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, Achnanthes elongata and Achnanthes squaliformis, found on the carapaces 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 Achnanthes groenlandica var. phinneyi and Achnanthes pseudogroenlandica. The two taxa 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