Obovate (inversely ovate, or narrow toward the central area and wider toward the apices), with a concavity in each side, like the body of a violin.
An internal chamber on the valvocopula of the genus Mastogloia. Usually found in a row on each side of the valvocopula. Plural is partecta. The partecta secrete strands of mucilage through tubes running to the outside of the diatom valve.
The group of bilaterally symmetric diatoms. This is a heterogeneous group that includes araphid, monoraphid, and biraphid taxa. In older taxonomic systems, pennate diatoms are contrasted with the centric diatoms. Note, however, that these distinctions are artificial, and pennate and centric groups are not natural evolutionary lineages.
The axis of the valve which is perpendicular to the center of the valve face. In centric diatoms, the center is the meeting point of the radii. In pennate diatoms, the center is the meeting point of the apical and transapical axes.
In diatoms, the pigmented organelle that is the site of photosynthesis.
Plastids contain carotinoid pigments such as beta-carotene, diatoxanthin, diadinoxanthin, and fucoxanthin. They also contain a combination of chlorophylls a, c1, c2, and c3, depending on the species.
Most diatom plastids appear golden brown because the carotenoid pigments mask the color of the chlorophylls.
A hyaline thickening of silica at the valve apices in some pennate species. The genus Sellaphora possesses variable development of polar bars.
A transapical undulation, or elevated ridge, of the external valve face. The porca is particular to the genus Surirella. Plural form is porcae.
An area of fine pores, or perforations, through the diatom valve. It is the site of the extrusion of mucopolysaccarides for making stalks and pads.
A small perforation through the valve. Plural form is porelli. Groups of closely packed porelli occur in ocelli, pseudocelli and apical pore fields.
In raphid diatom ontogeny, the side of the valve formed from the initial branching of the raphe sternum. See secondary side.
The growth habit of lying flat, firmly attached by mucilage to a surface. Example surfaces include rocks, filamentous algae, macrophytes, and even other diatoms.
A valve apex having the appearance of being drawn out or pulled apart.
The portion of a raphe branch near the central nodule of a valve. The proximal raphe ends border the central nodule of a valve. See distal raphe.
A silica plate extending internally from the apical portion of the valve. To contrast, a pseudoseptum is part of a valve, while a septum is part of a copula, or girdle band. The pseudoseptum occurs in some species of Gomphonema, Gomphoneis, Stauroneis, and Navicula. Plural form is pseudosepta.
A structure embedded in or associated with the plastids, involved with fixing carbon dioxide. Assumes many shapes, from spheres to plates to rods. A diatom cell may have several. Visible with transmission electron microscopy, but usually indistinguishable with light microscopy. From Greek for “nut-like”.
Pyrenoids are composed primarily of the crucial enzyme, rubisco, and are often traversed by thylakoid membranes continuous with stromal thylakoids in the plastids. Pyrenoids concentrate the often low amounts of carbon dioxide in water for use by rubisco, which incorporates carbon dioxide into the first step of carbohydrate production by the Calvin cycle.