Shionodiscus karianus Georgiev & Gololobova

Shionodiscus karianus Georgiev and Gololobova (2022).

Description

Valves circular and heavily silicified, diameter 30.8 (26–54) μm, no external projections of processes. Areolae pattern on valve face curved in tangential rows or in sectors of radial or sub-radial rows. Striae 10 in 10 µm, areolae 7 (7–11) in 10 µm from centre towards mantle and 8 (8–13) near mantle zone. Areolae loculate with internal domed cribra, slightly elevated relative to surrounding hyaline area, 6–7 (10–16) cribrum pores in 1 μm. One (1) central fultoportula process (CFP), operculate with 4 (4) satellite struts, 4 (4) pores with cowlings. Rimoportula radially orientated and located 1 (0–2) areolae, 1.2 µm (1.3–3.4) µm distance, from CFP. Four (4) marginal fultoportula processes (MFP), strutted, have 4 satellite pores, 15 (13–35) per valve. MFP internally long, more or less evenly placed around valve margin, 1.6 (1.5–2.4) in 10 µm, 4–6 (2–7) areolae between processes and 1.7–2.8 (2.7–6.5) µm apart.

Diagnosis

External valves, girdle band images and external valve ultrastructural details are lacking at this time. The Shionodiscus species closest to this specimen are S. bioculatus, S. bioculatus var. exiguus, S. biporus, S. centrus, S. gaarderae and S. variantius. All have an operculate CFP with a rimoportula that is located nearby or midway between the valve margin and CFP. All of the above species have areolae densities that are over double that of the SHW specimen. Only S. bioculatus and S. gaarderae have a rimoportula that is immediately adjacent to a central areola; however, the separation is more than 1 areolae distant, valve areolae density is too high, at 16–23 in 10 µm and MFP are 5–7 µm apart (Hasle and Syvertsen (1997): table 14, Ferrario et al. (2018): table 1, Georgiev and Gololobova (2022): table 2). Although S. bioculatus has been previously reported in the Salish Sea, the morphometric data of this SHW specimen are more than adequate to place it as Shionodiscus karianus.

Notes

iNaturalist ID: 322791476 (Fig. 34).