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 structurally related marine Cocconeis species, C. pseudomarginata Gregory and C. caribensis sp. nov., is described. Cocconeis pseudomarginata has very dissimilar valves: the sternum-valve bears an externally depressed sternum, a longitudinal thickening, external elongated and internal circular areola openings; the raphe-sternum valve is concave between the apical axis and the valve margin. The type material of C. pseudomarginata and C. vitrea has been studied for comparison. Cocconeis caribensis sp. nov., an epiphyte on mangrove roots in the Caribbean Sea, is distinguished by strongly concave and convex valves, high stria density (28234 in 10 mm in the sternum valve), the 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 sternum valve of C. caribensis sp. nov. are similar to those of C. pseudomarginata.