The Pinguiophyceae classis nova, a new class of photosynthetic stramenopiles whose members produce large amounts of omega-3 fatty acids

The Pinguiophyceae class. nov., a new class of photo‐synthetic stramenopiles (chromophytes), is described. The class includes five monotypic genera, Glossomastix, Phaeomonas, Pinguiochrysis (type genus), Pinguio‐coccus and Polypodochrysis. These algae have an unusually high percentage of polyunsaturated fatty acids, especially 20:5 (n‐3)(EPA, eicosapentaenoic acid). These fatty acids are the basis for choosing the Latin noun ‘Pingue’ (= fat, grease) as the root for the class name. Analyses of nuclear‐encoded 18S rRNA and chloroplast‐encoded rbcL gene sequence data showed that these algae formed a monophyletic group that could not be placed in any other class. Morphologically, the species are all single‐celled microalgae from picoplanktonic size to over 40 urn in length. Each cell has one (or two) typical chloroplast(s) with a girdle lamella and a surrounding chloroplast endoplasmic reticulum. Pyrenoids occur within the chloroplast, varying from embedded to stalked, and membranes penetrate into the pyrenoid in all five genera. Phaeomonas has motile cells with two flagella, and the forward‐directed flagellum bears mastigonemes (tripartite flagellar hairs). Two other genera (Glossomastix, Polypodochrysis) produce zoospores that possess only one smooth flagellum (no mastigonemes), and this flagellum apparently is the mature flagellum, a feature previously unknown in the photosynthetic stramenopiles. The major carotenoid pigments in the pinguiophytes are fucoxanthin, violaxanthin, zeaxanthin and P‐carotene, as well as chlorophyll a and chlorophyll c‐related pigment(s). These features support recognition of the Pinguiophyceae class. nov. as a unique group of algae.