Cavinula davisiae Bahls

Cavinula davisiae Bahls (Figs 93–98)

Valves lanceolate to lanceolate-elliptic, with rounded apices. Valve length 14–31 µm, width 7.5–10 µm. Striae composed of round to elliptic areolae, 32–36 in 10 µm. Areolae around central area elongated; internally covered with hymenes. Stria density 24–26 in 10 µm. Striae radiate throughout. Central area broadly rounded and formed by alternating long and short striae along both valve margins. Axial area narrow and linear, internally axial area thickened, along raphe terminating prior to central area. Externally, raphe filiform, proximal raphe fissures tear-drop in shape and distal fissures hooked to opposite sides on valve face. Internally, proximal fissures terminate as simple pores, terminal fissures end in helictoglossae.

Type:— Clover Lake, Mount Rainier National Park, Pierce County, Washington, USA; Bahls 2013, fig. 48 (holotype). Here presented in Figs 93–98 from isotype slide ANSP GC65165.

Observations:— On initial observation, this taxon is similar to C. cocconeiformis, C. variostriata (Krasske) Mann and C. lapidosa (Krasske) Lange-Bertalot. Cavinula davisiae is differentiated by a lower stria density and more pronounced central area; it is further differentiated from C. variostriata (Lange-Bertalot et al. 1996, fig. 19: 27–30) by the smaller central area and the lanceolate not linear valve. In addition, C. lapidosa has a linear valve outline and panduriforme shape of the central area (Lange-Bertalot et al. 1996, fig. 19: 22–26).

Distribution:— Cavinula davisiae is found across western northern North America and common in circumneutral waters with low conductivity. Previously, specimens were identified under Navicula variostriata Krasske. Validated identifications for this taxon are from Adak Island, Alaska (Hein 1990, originally as C. variostriata) and coastal British Columbia (Pienitz et al. 2003, originally as C. cf. variostriata).

Distribution Records:— Bahls, L. (2013, fig. 15: 43–51, fig. 15: 48= holotype, Washington).