It is classed as a cryptophyte. Guillardia theta was the first cryptophyte to have its nuclear genome sequenced. This Geophyte (Cryptophyte) forms bulbs as resting buds. Members of the genus "Dinophysis" have a phycobilin-containing chloroplast taken from a cryptophyte. Naturally occurring anion-conducting channelrhodopsins (ACRs) were subsequently identified in cryptophyte algae. The cryptophyte nucleomorph found in "M. rubrum" is lost in "D. caudata". Cryptophyte chloroplasts contain a nucleomorph that superficially resembles that of the chlorarachniophytes. Inside cryptophyte chloroplasts is a pyrenoid and thylakoids in stacks of two.