Gyrosigma tenuissimum
Family: Pleurosigmataceae
Gyrosigma tenuissimum image
Gyrosigma tenuissimum  

Species Description: The species was recently typified by Sterrenburg et al. (2014) and included this new variety that is known only from the IRL so far.

The valves of the type variety are very delicate, 47-150μm long and 6-7μm wide, practically parallel-sided and straight for most of their length, becoming slightly sigmoid near the acute apex. The raphe sternum is non-sigmoid over most of its length, curving only near apices. Transverse striae are 19-22 in 10μm, longitudinal striae about 42-48 in 10μm. No hyaline central area is visible in the light microscope, central raphe node minute, with the external central raphe fissures not visible.

The variety gundulae (Fig. 1, variety type, LM) has comparable striation and shape to the type variety, but differs in that it is more robust (159-190µm long and 9.5-11µm wide) and is somewhat broader at the apices. In SEM externally, the central raphe fissures are extremely approximate, overlapping and oppositely deflected (Fig. 2, central valve exterior, SEM). External areolar fissures of two adjacent areolar rows often join in the shape of the letter V (Fig. 2). There is a characteristic small accessory fissure at the apex (Fig. 4, valve apex, exterior SEM, arrow). Internally (Fig. 3, central valve interior, SEM), the foramina of the areolae are apically elongated and more or less rectangular. The central raphe node is tiny, with a square central depression, and four (or more) siliceous nodules. Distally, the raphe ridge becomes twisted so that the raphe fissure opens laterally (Fig. 3). Living cells have two elongate, and sometimes contorted, chloroplasts (Fig. 5, three cells from a crude culture, phase contrast, cell length ~170µm).

The variety has been found only in the IRL system, and is fairly common throughout the year at many locations (e.g. Hargraves & Hanisak 2011).

Hargraves PE, Hanisak MD. 2011. The significance of chlorophyll size fractionation in the Indian River Lagoon, Florida. Florida Scientist 74: 151-167.

Sterrenburg FAS, DeHaan M, Herwig WE, Hargraves PE. 2014. Typification and taxonomy of Gyrosigma tenuissimum (W. Sm.) J.W. Griffith & Henfr., comparison with Gyrosigma coelophilum N. Okamoto & Nagumo and description of two new taxa: Gyrosigma tenuissimum var. gundulae var. nov. and Gyrosigma baculum sp. nov. (Pleurosigmataceae, Bacillariophyta). Phytotaxa 172: 71-80.

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 tenuissimum image
Gyrosigma tenuissimum  
Gyrosigma tenuissimum image
Gyrosigma tenuissimum  
Gyrosigma tenuissimum image
Gyrosigma tenuissimum  
Gyrosigma tenuissimum image
Gyrosigma tenuissimum  
Gyrosigma tenuissimum image
Gyrosigma tenuissimum