A valve end, or apex, having the shape of a head, or the shape of a rounded knob.
Other terms for valve ends include subcapitate (less strongly capitate), rostrate, and subrostrate (less strongly rostrate). Subcapitate and subrostrate are quite similar and many taxa may be described as having subcapitate to subrostrate valve ends.
In general, capitate and subcapitate ends are more expanded than the most narrow point on the valve, while rostrate and subrostrate 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. Often thickened, both in valve and girdle views. It is the site where the silica deposition vesicle deposits the first silica during valve formation.
The series of linking, siliceous bands associated with a
Each band is called a girdle band, or copula (from Latin for band or link; plural is copulae). Plural form is cingula.
Each valve has its own cingulum and the valves of most diatoms have a cingulum. The epivalve has the epicingulum and the hypovalve has the hypocingulum. The epicingulum always overlaps the hypocingulum. The two cingula together compose the girdle, or cincture.
Girdle bands may be secreted after the vegetative cell division that produced the valve. In other words, while the deposition of the valve is tied to cell division, the deposition of its girdle bands may not be.
Having the shape of a club. Usually applied to describe the asymmetry of Gomphoneis and Gomphonema.
A valve surface covered with small bumps or elevated bits of silica.
The narrow, hyaline area on the valve mantle in the genus Aulacoseira. A small furrow, or sulcus, separates the collum from the portion of the valve mantle with areolae. See also ringleiste.
A thin siliceous covering on the external valve surface. The conopeum may be slightly to distinctly elevated from the valve face and may partially or completely cover the striae and extend to the valve margin. This structure is visible only with the 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, Nitzschia and Sellaphora.
Striae that lean toward the central nodule, with the sternum as the origin. Convergent striae may occur throughout the valve, at the valve center, or at the valve apices. In contrast, striae are radiate, or divergent, if they lean away from the central nodule, with the sternum as the origin.
An unornamented, elongated thickening of the valve. Usually refers to a thickening parallel to the striae. Plural form is costae. From Latin for rib.
See also axial costa.
An internal valve occurring in species in the genus Craticula. This craticular valve consists of a raphe-sternum and robust transverse bars. Frustules with normal morphology produce the craticular valve under conditions of high solute concentration. The formation of these internal valves 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.