Cyclotella bodanica var. intermedia

Observations

Contributor: William Daniels - June 2012
Length Range: 12-34 µm
Striae in 10 µm: 11-13

Description

Valves are disc-shaped and concentrically undulate, with both concave and convex centers. The valve is divided into two distinct parts, with the central part roughly 1/3 of the total diameter. Striae are alveolate and multiseriate, with 3-4 rows of fine porelli which are not readily seen in LM. Porelli spacing within rows is 45-50 in 10 µm. The striae are of mostly the same length, but are variably interrupted by short stria that give the appearance of branching costae near the margin. Isolated rimoportulae with simple external openings are observed at the central ends of 2 or 3 shortened striae. These rimoportulae are sometimes evenly spaced around the diatom and sometimes not. Internally, the rimoportulae are long, thin, and oriented oblique or perpendicular to the striae. The central area contains areolae and fultoportulae of varying size that are arranged randomly, to somewhat radially. Under SEM, the areolae are internally covered by cribra while the fultoportulae are bordered by 3 satellite pores. There may be a thin hyaline area (annulus) isolating the central-most areolae. Marginal fultoportulae are evenly spaced and located at the marginal ends of the costae.

Note that the combination and elevation in rank to species published in Houk et al. (2010), Cyclotella intermedia (Manguin) Houk, was invalid because it did not refer to the validating description of the species (Kociolek and Reviers 1996).