Described by Hill and Wetherbee; type species Proteomonas sulcata (marine; Hill and Wetherbee 1986).

Only one strain has been sequenced (Marin et al. 1998; Deane et al. 2002; Hoef-Emden et al. 2002). Proteomonas sulcata was the first cryptophyte for which a dimorphism was reported (Hill and Wetherbee 1986). In molecular phylogenies inferred from nucleomorph SSU rDNA sequences, this strain seems to be related to the other two PE545-containing clades with free nucleomorphs (Guillardia/Hanusia and Geminigera/Plagioselmis/Teleaulax genus complex), whereas its position is not resolved in nuclear SSU rDNA phylogenies (Hoef-Emden et al. 2002).

• Type of biliprotein: PE545
• Nucleomorph free in periplastidial space
• Dimorphic
• Light microscopy: reddish cryptophytes, one bilobed plastid with a pyrenoid, haplomorphs smaller than diplomorphs
• Ultrastructure of haplomorph: inner periplast component with hexagonal plates, surface covered by hexagonal scales, furrow only, non-keeled rhizostyle
• Ultrastructure of diplomorph: sheet-like inner periplast component, surface covered by fibrils and rosulate scales, furrow only, keeled rhizostyle