platysulcus platysulcus platysulcus (from latin platy 'wide', and sulcus 'furrow') is an eukaryotic microorganism that was recently discovered to be the earliest diverging lineage of the heterokont phylogenetic tree. it is the only member of the family platysulcidae, order platysulcida and class platysulcea, of uncertain taxonomic position within the phylum bigyra. it contains the only species p. tardus. platysulcus scientific classification domain: eukaryota clade: diaphoretickes clade: sar clade: stramenopiles phylum: bigyra class: platysulceacavalier-smith, 2017 order: platysulcidacavalier-smith, 2017 family: platysulcidaeshiratori, nkayama & ishida, 2015 genus: platysulcusshiratori, nakayama & ishida, 2015 species: p. tardus binomial name platysulcus tardusshiratori, nkayama & ishida, 2015 morphology platysulcus is a gliding biflagellate, with a short anterior flagellum, a long posterior flagellum, and a flagellar apparatus typical of stramenopiles. it has tubular mastigonemes on the anterior flagellum. it contains mitochondria with tubular cristae. the basal body and the transitional region of the flagella lack ring-shaped or helical structures. the two flagellar roots consist of 11 microtubules forming an “l”-shape. its cells are oval or ovoid in shape, around 5.62 μm in length and 3.76 μm in width. the anterior flagellum is around 9 μm in length, and the posterior measures around 17 μm. they contain extrusomes and a large, flat vesicle surrounding the cytoplasm where the nucleus, mitochondria, and microbodies are found. ecology platysulcus was isolated from sedimented detritus on seaweed collected near ngeruktabel island, palau. it is a free-living phagotrophic protist, bacterivorous and marine. phylogeny and taxonomy phylogeny phylogenetic analyses recover platysulcea as the earliest diverging lineage of stramenopiles, sister to a clade containing bigyra and gyrista. stramenopiles gyrista ochrophyta pseudofungi bigyromonadea bigyra sagenista opalozoa platysulcus tardus taxonomy despite the phylogenetic results, platysulcea has been classified as part of the phylum bigyra. class platysulcea cavalier-smith, 2017 order platysulcida cavalier-smith, 2017 family platysulcidae shiratori, nkayama & ishida, 2015 platysulcus shiratori, nkayama & ishida, 2015 p. tardus shiratori, nkayama & ishida, 2015