Valve ends that are expanded into a rounded knob are termed capitate. Note that the shape terms subcapitate and subrostrate are quite close, and that many taxa can be described as possessing subcapitate to subrostrate ends. In general, capitate (and subcapitate) ends are more expanded than the most narrow point, while rostrate (and subrostate) ends are not more expanded than the most narrow point.
A type of central process unique to the genus Orthoseira. The internal openings are simple, while the external openings are composed of well-defined collars.
In raphid diatoms, the thickly silicified area located between the proximal raphe slits. The central nodule is the site where the first silica is deposited in by the silica deposition vesicle in valve formation. The central nodule is often thickened, both in valve and girdle views.
Cingulum is a term that refers to all of the collective elements of the diatom girdle. The cingulum is made up of delicate silica bands (= girdle bands, copulae) that join the two valves of a frustule. Most diatoms possess a cingulum, although some may not. The silica structures of the cingulum may be secreted after vegetative cell division that produces the diatom valve; that is, while the deposition of the silica valves are tied to cell division, the deposition of the cingulum may not be tied to division.
Club shaped; usually applied to describe the asymmetry of Gomphoneis and Gomphonema.
A valve surface covered with small bumps or elevated bits of silica is termed 'colliculate'.
A structure found in the genus Aulacoseira. The collum is the narrow, hyaline area on the valve mantle. A small furrow, the sulcus, separates the collum from the portion of the valve mantle with areolae.
A thin siliceous covering over the striae on the external valve surface. The conopeum may be slightly to distinctly elevated from the valve face. The width of conopea is variable, but may extending to the valve margin. This structure is visible with scanning electron microscope. Conopea have been found to contain symbiotic nitrogen-fixing cyanobacteria and are found in a number of genera, including Fallacia, Lyrella, Microcostatus and Sellaphora.
Striae angled or curved away from the central nodule are termed convergent striae. Striae may be convergent in a specific part of the diatom valve. For example, the striae may be convergent throughout the valve, convergent only at the center valve, convergent only at the ends, etc. Convergent striae are opposite of radiate (divergent) striae.
Plural, costae. A general term for a unornamented thickening of silica on the valve face.
Craticula is a term applied to internal valves that are formed by species in the genus Craticula. Frustules that are normal in morphology produce the craticular stage under conditions of high solute concentration. The craticular valves consist of a raphe-sternum and robust transverse bars. These internal valves are formed within normal valves and, unlike normal valves, their formation is not linked to mitosis.
A thin covering of silica that possesses fine pores. The cribrum is located on the internal opening of an areola. This structure is visible only with scanning electron microscopy.
Cross-shaped, usually applied to describe the valve outline of some diatoms.