Fragilaria joachimii Kahlert, type population

(Fig. 4)

Basionym: Fragilaria joachimii Kahlert in Kahlert et al., Journal of Phycology 55: 963, fig. 5 (2019).

MORPHOLOGY

LM (Fig. 4 A-T)

Frustules in girdle view rectangular, in culture linked forming long chains of up to several tens of cells (Fig. 4 S-T). Valves linear with parallel margins and broadly rounded, protracted, rostrate, never capitate apices. Shoulders poorly developed, gradually tapering into the apices. Centrally, valves often slightly inflated. Valve dimensions (n = 40): valve length 14-28 µm, valve width 3.5-4.5 µm (length 5-31 µm, width 3.3-4.6 µm in the protologue, Kahlert et al. 2019). Axial area very narrow linear, not widening towards the central area. Central area large, forming a broad, often asymmetrical, inflated fascia, due to several shortened striae on one side. Striae parallel throughout, becoming weakly radiate near the apices, 14-16 in 10 µm, often irregularly spaced. Areolae not discernible in LM.

SEM (Fig. 4 U-X)

Girdle composed of several open, perforated copulae (Fig. 4 U-V). Frustules not linked using linking spines but by mucus (Fig. 4U, arrows). Large, irregularly shaped mantle plaques present on the mantle edge (Fig. 4V). Mantle striae continuing from the valve face till halfway or 1/3 of the mantle edge (Fig. 4V). Striae uniseriate, composed of small, rimmed, rounded areolae (Fig. 4 W-X), individually covered by external hymenes (Fig. 4X). Virgae between the striae weakly raised (Fig. 4W). One rimoportula present at one apex, in line with the last stria at the apex (Fig. 4X). Apical pore field present at both apices (Fig. 4X). Small spines and granules scattered throughout the entire valve face and mantle (Fig. 4 W-X).