Chloropicophyceae, a new class of picophytoplanktonic prasinophytes.

Prasinophytes are a paraphyletic group
of nine lineages of green microalgae that are currently classified either at
the class or order level or as clades without formal taxonomic description. Prasinophyte
clade VII comprises
picoplanktonic algae that are important components of marine phytoplankton
communities, particularly in moderately oligotrophic waters. Despite first being cultured in the 1960s, this
clade has yet to be formally described. Previous phylogenetic analyses using the
18S rRNA gene divided prasinophyte clade VII into three lineages, termed A, B
and C, the latter formed by a single species, Picocystis salinarum, that to date has only been found in saline
lakes. Strains from lineages A and B cannot be distinguished by light microscopy
and have very similar photosynthetic pigment profiles corresponding to the prasino-2A
pigment group. We obtained phenotypic and genetic data on a large set of prasinophyte
clade VII culture strains that allowed us to clarify the taxonomy of this
important marine group. We describe two novel classes, the Picocystophyceae and
the Chloropicophyceae, the latter containing two novel genera, Chloropicon and Chloroparvula, and eight new species of marine picoplanktonic green
algae.