Pyramimonas robusta sp.nov., a new punctate species, and a reappraisal of the subgenus Punctatae

Abstract

The ultrastructure of a new punctate species, Pyramimonas robusta, is described and, by comparison with features of Pyramimonas olivacea N. Carter and Pyramimonas mucifera Sym et Pienaar, has allowed for a more defined delimitation to the subgenus Punctatae McFadden. Features, in addition to the obvious character of puncta, which are considered characteristic of this subgenus, include a benthic nature, a chloroplast with a ventral groove coincident with the left and right sinuses, box scales with spines on their side walls, crown scales with eccentric crosses on their base plates, segmented T hairs, limuloid scales with three subsidiary spines and five subsidiary radial ribs, a 3-1 type flagellar apparatus, a basal body with a long region of triplets with longitudinal fibrils separating proximal and distal cartwheel structures, and a 3(2/1):4 or 3:3(2/1):2 microtubular root system. Although as a suite these are characteristic, a great deal of the individual features are shared with other subgenera, specifically subgroup 2 members of the subgenus Trichocystis McFadden but especially members of the subgenus Pyramimonas McFadden. Features originally considered diagnostic that now are questionable include pyrenoid structure and starch investiture and the bilayered nature of the eyespot. Key words: Punctatae, Pyramimonas, Pyramimonas robusta sp. nov., ultrastructure.