Pinaciophora rubicunda (Hertwig & Lesser, 1874) emend. Roijackers & Siemensma, 1988
Diagnosis: Cells globose with a diameter ranging from 15-25 µm (mean 22 µm). The plate-scales are broadly elliptical, discoid, 3.6-5.3 µm in diameter, with a distinct pattern of large perforations, 4-9 in number; usually there is one central hole, surrounded by 6 equal holes, showing a hexagonal pattern. The cytoplasm contains many small brown-reddish colored granules.
Ecology: Marine and brackish waters. The species has been recorded from Germany, in a sea water aquarium (Hertwig and Lesser, 1874 and likely from New Zealand (Schaudinn, 1896). I collected this species from the coast of southern Sweden, Baltic. Nicholls reports this species from the Canadian Pacific (2013).
Remarks: This species is easily distinguished from P. fluviatilis by the smaller cell diameter and the smaller plate-scales with fewer than 10 perforations. The broad elliptical plate-scales are distinguishable from the circular ones of P. fluviatilis. The plate-scales are almost identical to those of Rhabdiophrys thomseni, which species, however, also possesses spine-scales. Therefore, single plate-scales are not sufficient for distinguishing between these two species.
Nicholls (2013) gives following measurements for his Canadian specimens: Cell size 10 – 15 µm in diameter. Plate-scales circular to elliptic, 3.0 – 3.5 µm wide x 3.5 – 4.3 µm long, ornamented with usually one central hole in the distal layer of the scale surrounded by 5-7 generally equally-spaced holes 0.19 – 0.35 µm in diameter. Short segments of the internal meshwork in the space between the outer and inner scale layers could be seen through several of the holes in the outer (distal) layer (Figure ). A slightly thickened rim about 0.07 µm wide was present around the scale margin, presumably where the two layers were fused.