Bacterosira constricta (Gaarder) J. S. Park & J. H. Lee

Thalassiosira constricta Gaarder (1938): 6, fig. 6; Harris et al. (1995): 125, fig. 15; Hasle and Syvertsen (1997): 69 –70; Throndsen et al. (2007): 137.

Bacterosira constricta — Park et al. (2016 a).

Description

Frustules rectangular in girdle view, with slightly round valve edge. Cells in chains, often connected by chitin threads extruded from central fultoportulae; rarely solitary. Pervalvar axis length 17.8 (13.5–23.0) μm, sometimes exceeding length of valve diameter. Cells circular in valve view, diameter 21.9–22.7 (9.8–25.7) μm, with slight depression in centre. Clusters of 2 (0–14) fultoportulae present in valve centrs. Fultoportulae, with raised tubes, located on valve margin, 3–4 (5–7) in 10 µm. Single rimoportulae located mid-way between marginal fultoportulae. Areolar density, 36–44 per 10 μm on valve face, 37–46 per 10 μm on valve margin and 30 (41–51) per 10 μm on valve mantle.

Diagnosis

This specimen from Trincomali Channel has two central, buttressed, strutted processes instead of a cluster of tubes (fultoportulae) in the centre of the valve, which is unusual. Normally, for the two species of this genus, the buttresses are not apparent, though they are mentioned in Harris et al. (1995). All other morphological features of this specimen conform reasonably well with published accounts of Bacterosira constricta. This specimen is unlike the only other accepted species, Bacterosira bathyomphala (Cleve) Syvertsen & Hasle (Guiry and Guiry 2025). More specimens are required to examine the internal valve and girdle band morphology.

Notes

iNaturalist ID: 259444260. Mol. data: ERS 27217975, ERS 27218291, ERS 27218292, ERS 27218293, ERS 27218294, ERS 27218295, ERS 27218296, ERS 27218297, ERS 27218298 (Fig. 7).