Species Description: Cells are united into chains, mostly 4-16 cells long, with a complex three dimensional structure.  Each cell is cylindrical, with a deep mantle (Fig.1, chain in girdle view, modified from Pavillard 1916).  The valve surface has a circular array of 6-8 setae that emerge from the valve in the axis of the chain, then turn perpendicularly to the chain axis and fuse with setae of the adjacent cell. At about one third the seta length, each fused seta bifurcates and bends toward the posterior end of the chain.

The terminal cells of a chain are dimorphic. The upper terminal valve has 6-8 heavily siliceous non-bifurcate setae that spiral out from the valve (Fig. 2, SEM), and lie in the apical plane, often curving slightly up or down toward the axis of the chain. The lower terminal valve also has 6-8 heavily siliceous non-bifurcate setae (Fig. 3, SEM), but they curve strongly downward, becoming more or less parallel to the axis of the chain (Fig. 4, LM color). Both upper and lower terminal setae may have spirally arranged minute spines along their length (Fig. 2, 3). The upper terminal valve has a central rimoportula (Fig. 5, arrow; terminal valve interior).

Cell diameters vary from about 6-24µm, with a pervalvar axis of 25-50µm.  There are numerous small discoid chloroplasts.  This is a tropical species, more common in neritic areas, but also oceanic in Atlantic, Pacific, and Indian Oceans. In the IRL, it was found rarely in the Jupiter Inlet area in August 2008 and in the Haulover Canal in October 2010.

Pavillard J. 1916. Recherches sur les diatomées pélagiques du Golfe du Lion. Travail de l’Institut de Botanique de l’Université de Montpellier, Série mixte – Mémoire 5:7-62.

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.