The ultrastructure of Bathycoccus gen. nov. and B. prasinos sp. nov., a non-motile picoplanktonic alga (Chlorophyta, Prasinophyceae) from the Mediterranean and Atlantic

A non-motile, picoplanktonic species, Bathycoccus prasinos gen. et sp. nov. (Mamiellaceae, Mamiellales, Prasinophyceae) is described from the Gulf of Naples, Italy. Resembling a comma, the cells are greenish and ellipsoidal, and possess a layer of imbricated scales with spider web-like markings that covers the cell surface. The scales are almost circular and have radiating and concentric ribs. Eight spoke-like ribs radiate from the centre of each scale, their number increasing about twofold at the periphery, and five concentric ribs are usually formed. The cells normally contain one semilunar chloroplast, the central region of which lacks thylakoids and is usually occupied by a starch grain, although a well-defined pyrenoid is absent. Each cell contains one mitochondrion, a nucleus and a Golgi complex. The species is also reported from Norwegian coastal waters.