All Taxa

Gomphonemataceae: Didymosphenia

Frustules large, wedge-shaped in valve view, with a broad, bluntly rounded head pole, often a swollen centre and a rounded foot pole; wedge-shaped in girdle view; girdle deep (hence cells often lie in girdle view).

Frustules isovalvar, very slightly to noticeably asymmetrical with respect to the apical plane (with a tendency to be slightly ‘cymbelloid’).

Striae uniseriate, strongly radial with long and short striae alternating at the centre; areolae circular to quadrangular, very obvious in LM, occluded by complex flaps borne from the areola walls; a large area of many tiny pores is present at the base-pole, forming a pore field.

Axial area narrow, central area somewhat expanded, containing one to several isolated large pores (stigmata) on one side (the primary side).

Raphe central, straight or slightly curved; expanded externally at the centre to form raindrop-like endings; central internal endings hidden by silica overgrowth from the primary side; polar raphe endings bent towards the secondary side.

Girdle composed of several open bands. One complex chloroplast per cell, consisting of two X- shaped plates against the valves, connected by a substantial bridge on the secondary side of the cell (i.e. on the opposite side to the stigmata) containing a large pyrenoid.