Glossary terms starting with "P"
Panduriform
Obovate, with a concavity in each side, like the body of a violin
Partectum - chamber, locule
The genus Mastogloia possesses a distinct valvocopula (first girdle band). The valvocopula is marked by one to several internal chambers, called partecta, and tubes that open from the partecta to the outside of the diatom valve. The partecta function to secrete strands of mucilage from the cell.
Pennate
A bilaterally symmetric diatom. A heterogeneous group that includes araphid, monoraphid, and biraphid taxa.
Pervalvar axis
The axis that crosses the center of the apical and transapical axes.
Plastid - chromatophore, chloroplast
A membrane-bound organelle and the site of photosynthesis. Most diatom plastids appear golden brown due to carotenoid pigments (beta-carotene, diatoxanthin, diadinoxanthin, fucoxanthin), which mask the color of the chlorophyll molecules (chlorophylls a, c2, and c1 or c3)
Polar bar - transapical thickening
A polar bar is a hyaline thickening of silica, present at the apices in some pennate species. The genus Sellaphora possesses variable development of polar bars.
Porca - ridge surface, corrugation ridge, transapical valve undulation
A term applied to a particular structure in the genus Surirella. Porcae are transapical undulations, or elevated ridges, of the external valve face.
Porefield
An area of fine pores, or perforations through the diatom valve. Porefields function in the extrusion of mucopolysaccaride stalks, or pads, from the cell.
Porelli
Small, closely packed perforations through the valve. The small perforations in ocelli, pseudocelli and apical pore fields are often referred to as porelli.
Primary side
The primary side of a valve is the side that is formed from the initial branch of the sternum of raphid diatoms.
Prostrate
Many algae live attached firmly to a surface, such as rocks, macrophytes or other substrates. Species that 'lie flat' and are affixed to a surface are considered to have a prostrate habit of growth.
Protracted
Drawn out
Proximal raphe
The terminus of the two raphe branches near the center of the valve. The proximal raphe ends border the central nodule.
Pseudoseptum
A plate, or lamina, of silica projecting internally from the apical portion of the valve. Pseudoseptae are found in some species of Gomphonema, Gomphoneis, Stauroneis, and Navicula. Pseudoseptae are part of the valve, while septae are part of the copulae, or girdle bands.
Pyrenoid
Distinct, proteinaceous structure (often spherical), embedded in or associated with chloroplasts; in some, contains the enzyme RuBisCO; associated with starch in some diatoms