Gomphoseptatum pseudoseptatum (Giffen) Witkowski, Lange-Bertalot & Metzeltin

Gomphonema pseudoseptatum Giffen (1970): 13, figs. 29–32 — Medlin and Round (1986): 476, 477.

Gomphoseptatum pseudoseptatum — Witkowski et al. (2000): 222, pl. 60, figs. 22–26; Guiry and Guiry (2025).

Description

Frustules in girdle view weakly clavate with distinctive pseudosepta on both apices. Valves linear to linear-lanceolate, gradually tapering from obtusely rounded head pole to slightly produced foot pole. Length 40.7–63.1 (12–33.3) μm, width 4.6–4.9 (2.5–5) μm. Raphe straight, axial area narrow. Central area has moderately wide transverse fascia that extend to margins. Externally, raphe is central, straight and opens slightly laterally. Central raphe endings slightly expanded; pore-like, polar (distal) fissures are bent, hook-like and curved to one side like a question mark, then curve back to centre of pole and are heavily silicified. Transapical striae uniseriate and mostly parallel, 8–9 (10–16) in 10 μm in mid-valve, 12 in 10 µm near poles. Striae crossed by rim of silica that runs around circumference of valve. Half of each stria subdivided into pores with cribra-like complex (30–80 nm pores), round to transapically slightly elongate. Striae towards each apex are reduced to smaller, single, round pores with the same cribra-like feature. Internally, pseudosepta are well-developed and equal-sized. Raphe internal endings straight. Pores closest to central area reduced in size and without marginal pore.

Diagnosis

Morphologically, the illustrations in Giffen (1970), an unpublished image by Giffen (image A 1008 Sa 02: A. Witkowski pers. comm., 07-06 - 2023) and the description and images of G. pseudoseptatum in Witkowski et al. (2000) support placing the two specimens from Galiano Island into Gomphoseptatum pseudoseptatum.

Notes

iNaturalist ID: 258910629 (Fig. 21).