Pleurosigma rostratum
Family: Pleurosigmataceae
Pleurosigma rostratum image
Pleurosigma rostratum  

Species Description: This species is broadly lanceolate with very slightly sigmoid valves and bent rostrate apices (Fig. 1, exterior of entire valve, SEM). The raphe is nearly straight or slightly sigmoid, eccentric near the apices, and curved in opposite directions at the two ends. The raphe ends in the center are also bent in opposite directions (Fig. 2, exterior, valve central area, SEM). The axial area is quite narrow and the central hyaline area is small. Cell length (apical axis) of measured specimens is 70-83µm and 19-23µm wide. Transverse and diagonal striae are 23-27 in 10µm, crossing each other at an angle of about 65 degrees. Individual areolae are circular or oval near the central area, and slit-like near the margin (Fig. 2).

Pleurosigma rostratum closely resembles P. lanceolatum (Hustedt 1955), which has not been identified in the IRL system; the latter is often found in more northern environments. These specimens differ slight from the type description in the number of striae and the shape of the central area. It was found in the St. Lucie estuary at Stuart, and has been previously seen in the Gulf of Mexico and the Caribbean.

Hustedt F. 1955. Marine littoral diatoms of Beaufort, North Carolina. Bull Duke Univ Mar Sta 6: 1-67.

Annulus: A hyaline ring of slightly thickened silicon on a valve surface.

Areolae: A regularly repeated perforation through the cell wall.

Auxospore: A special cell that restores cell size; normally a result of sexual reproduction.

Auxospore Envelope: A hyaline envelope that surrounds the auxospore cell.

Auxosporulation: The process of auxospore formation.

Capitate: Head-shaped.

Fascia: A plain, unthickened transverse strip.

Foramina: Opening on one side of a complex areola.

Homothallic: Possessing both male and female capability in a single morphologically and physiologically identical cell.

Hyaline Line: An unperforated siliceous strip between two striae.

Interstriae: An unperforated siliceous strip between two striae.

Morphogenesis: A developmental sequence that causes an organism to develop its shape.

Mucilage: Glycoproteins and/or exopolysaccharides excreted by some diatoms.

Ocellus: A group of small pores surrounded by a thickened hyaline rim and raised from the surface of the valve.

Oogamous: Sexual reproduction in which the sperm is small and motile, and the egg is larger and nonmotile.

Oogonia: Female gametangia.

Otaria: Membranous costae that occur opposite each other on a valve, especially the genus Rhizosolenia.

Pili: Long siliceous hairs on a diatom valve.

Poroid: Simple unchambered hole through a diatom valve.

Pseudoseptum: A siliceous projection to the cell interior at the edge of the valve.

Rimoportula: A tubelike opening through the cell wall with an internal flattened tube or lip-like slit; also called labiate process.

Rimoportula Tube: The external portion of a rimoportula.

Rostrate: The blunt tapered end of a valve, shaped like a beak.

Spermatogonangia: In sexual reproduction, the cell that produces sperm cells.

Spinules: Little spines.

Uniseriate: Arranged in a single series of cells.

Vegetative Cells: Cells that are a result of asexual division.

Pleurosigma rostratum image
Pleurosigma rostratum  
Pleurosigma rostratum image
Pleurosigma rostratum