Gyrosigma reversum
Family: Pleurosigmataceae
Gyrosigma reversum image
Gyrosigma reversum  

Species Description: This distinctive diatom differs from many Gyrosigma species in that it is not particularly sigmoid (Fig. 1, entire valve, SEM). The valves are narrow, somewhat lanceolate, tapering to elongate ‘spoon-shaped’ apices (Sterrenburg 2000), making the cells quite unmistakable. The cells are 175-230µm long and 8.5-12µm wide, with 24-30 transverse striae in 10µm and approximately the same for longitudinal striae (Fig. 2, external valve apex, SEM). Each stria is composed of areolae with externally opening slits. The raphe is approximately median, shifting to the convex margin near the valve apices (Fig. 2). The convoluted taxonomy of this and related species is discussed by Sterrenburg (2000). The IRL examples differ somewhat in their measurements from the examples described by Sterrenburg from Indonesia. Although one of the characteristics of G. reversa, as originally described by Gregory (1857), is the dilation of valve tips in opposite directions (Fig. 3, from Gregory 1857), and this example does not show that (Fig. 1) because the cell is twisted, all other characteristics place it in G. reversum rather than the similar G. naja. The apparent delicate nature of the narrowing probably permits this twisting during drying (Sterrenburg FAS, personal communication, 17 May 2013).

G. reversum is primarily a tropical benthic species, found worldwide. It is quite rare in the IRL, and was found near the Sebastian Inlet, in the St. Lucie estuary, and near the Jupiter Inlet.

Gregory W. 1857. On new forms of marine diatomaceae found in the Firth of Clyde and in Loch Fine. Trans Royal Soc Edinburgh 21: 473-542.

Sterrenburg FAS. 2000. Studies on the genera Gyrosigma and Pleurosigma (Bacillariophyceae). Gyrosigma reversum (Gregory) Hendey and G. naja (Meister) Sterrenburg. Proc Acad Nat Sci Philadelphia 150: 301-304.

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.

Gyrosigma reversum image
Gyrosigma reversum  
Gyrosigma reversum image
Gyrosigma reversum  
Gyrosigma reversum image
Gyrosigma reversum