Gyrosigma hummii
Family: Pleurosigmataceae
Gyrosigma hummii image
Gyrosigma hummii  

Species Description: In the original description, valves are slightly sigmoid, broadly linear to lanceolate with obtuse obliquely rounded ends (Fig. 1, holotype, from Hustedt 1955; and Fig. 2, entire valve, SEM). The raphe is sigmoid with a narrow axial area and a small rhomboid central area. The central raphe ends are slightly deflected to the same side and do not overlap (Fig.3), whereas the holotype drawing shows the raphe ends not bent (Fig. 1). Striae are composed of areolae with slotted exteriors (Fig. 3), numbering 13-15 per 10µm for transapical, and about 12-13 per 10µm longitudinal, increasing to about 16-17 in 10µm near the margin.  The valves are 120-190µm long and 27-30µm wide in the original description, but the few examples seen were 112-126µm in length and 25-26µm in width. It is closely related to G. simile (Grun.) Boyer, and the distinction between the two is not nearly as evident as Hustedt (1955) indicates.

The species is distinctive because of its length:width ratio of 4 to 6; but it has been seen only in the northern IRL and the Banana River. Navarro (1982) also reports it as rare.

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

Navarro JN. 1982. Marine diatoms associated with mangrove prop roots in the Indian River, Florida, U.S.A. Biblio Phycol 61: 1-151.

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 hummii image
Gyrosigma hummii  
Gyrosigma hummii image
Gyrosigma hummii  
Gyrosigma hummii image
Gyrosigma hummii