Two marine species of Cocconeis Ehrenberg (Bacillariophyceae): C-pseudomarginata Gregory and C-caribensis sp nov.

Using light and electron microscopy, the frustular morphology of two struct urally related marine Cocconeis species, C. pseudomarginata Gregory and C. caribensis sg. nov., is described. Cocconeis pseudomarginata has very dissi milar valves: the sternum-valve bears an externally depressed sternum, a lo ngitudinal thickening, external elongated and internal circular areola open ings; the raphe-sternum valve is concave between the apical axis and the va lve margin. The type material of C. pseudomarginata and C. vitrea has been studied for comparison. Cocconeis caribensis sp. nov., an epiphyte on mangr ove roots in the Caribbean Sea, is distinguished by strongly concave and co nvex valves, high stria density (28-34 in 10 mu m in the sternum valve), th e presence of hyaline submarginal areas between the sternum and the margin in the sternum valve, and the sigmoid sternum and raphe-sternum The areola structure and the morphology of the valvocopula and the fimbriae of the ste rnum valve of C. caribensis sp. nov, are similar to those of C. pseudomargi nata.