Pleurosigma cf. planctonicum Simonsen

Division: Chromophyta
Class: Bacillariophyceae
Order: Bacillariales
Suborder: Bacillariineae
Family: Naviculaceae Kützing
Genus: Pleurosigma Smith
Scientific name: Pleurosigma cf. planctonicum Simonsen

Species: cf. planctonicum

Reference:
Simonsen, 1974: p. 46, Pl. 30 a-d.

Description:
Valves lanceolate, slightly sigmoid near the ends, with flat valves and very acute, protracted ends, about 300-600 µm long, 40-75 µm wide. Raphe straight, before the ends sigmoid, central in the middle, eccentric toward the ends, central pores very approximate. Axial area very narrow, central area absent.Oblique striae about 30 in 10 µm, crossing each other at an angle of about 60º. Transapical striae always perpendicular to the raphe, about 28-30 in 10 µm in the middle, somewhat wider (ca. 27) near the ends; the striation is hardly visible (Simonsen, 1974).

Dimensions:
Cells length 300-360 µm; width 38-44 µm.

Distribution:
Mainly littoral species, but is frequently found in the plankton.

Sites of occurrence in RSA:
In Winter 2006 Cruise, it was present in small numbers at scattered stations (refer sites map). Species has been previously reported from the Indian Ocean and the inner RSA (Simonsen, 1974).