All Taxa

Fragilariaceae: Ulnaria

Cells typically long and thin, lying in valve or girdle view; valves linear or linear-lanceolate, with rounded, rostrate, capitate or swollen ends.

Frustules isopolar, isovalvar, bilaterally symmetrical.

Striae uniseriate, parallel; areolae small, circular. Marginal spines absent. Both apices with a large area of small pores (apical pore field) through which mucilage is secreted. In addition, a rimoportula is found close to each apex.

Axial area narrow. Central area variable; often forming a broad almost plain transverse area (fascia) though faint ‘ghost striae’ may be present within it.

Girdle of several bands including some closed hoops.

Two elongate chloroplasts per cell, located along the valves, though in unhealthy material these may split up, giving the appearance of many small discoid chloroplasts.