Cavinula kernii Cvetkoska, Hamilton, Levkov & Potapova 2014, sp. nov.

Cavinula kernii Cvetkoska, Hamilton, Levkov & Potapova sp. nov. (Figs 181 –192)

Valves elliptic-lanceolate with rounded apices. Valve face flat, sharply bent (not gradually curved) at margin onto mantle. Valve length 14–17 µm, width 7–8 µm with 22–24 stria in 10 µm. Striae radiate throughout; short and long striae alternate around central area. Striae uniseriate, composed of fine, rounded to elliptic areolae, 25–30 in 10 µm. Internally, areolae positioned between thickened costae and covered with hymenes. Axial area narrow, linear, transforming into a small rounded central area. Raphe linear, externally, proximal and the distal raphe features small pores; distal raphe endings do not extend onto valve mantle (i.e. terminate on the valve face). Internally, raphe positioned on elevated sternum; both, proximal and distal raphe fissures terminate with a helictoglossa. Copulae open, with one row of pores.

Type: — CALIFORNIA, USA: Kern River, Kernville, collection date: September 13, 1993, collected by B.L. Porter (holotype! slide ANSP GC 101724b, holotype! designated here, Accession No. ANSP GC 101724b, holotype specimen = Fig. 185; isotypes: CANA 105729).

Etymology:–– The specific epithet (kernii) refers to the type locality, Kern River.

Differential diagnosis:–– Cavinula kernii most resembles C. mollicula Hustedt in valve outline and structural form (Lange-Bertalot & Metzeltin (1996, fig. 24: 10–12, fig. 114: 5). There are minor differences in valve outline (more linear in C. kernii), central area (more evident in C. kernii), and the absence of scattered areolae at the terminal nodule (scattered pores present in C. mollicula). Lange-Bertalot also proposed that Navicula orbis Carter and Navicula arenula Hohn & Hellerman are synonymous with C. mollicula, which suggests that a number of similar taxa need to be considered in a more complete examination of this group of valve forms.

C. cocconeiformis f. elliptica is also similar in valve shape and size. C. kernii is distinguished by the simple poroid (not deflected) terminal raphe fissure. In addition there is an isolated row (ca. 12 areolae) along the base of the mantle of C. kernii and no other areolae in the terminal area, in contrast to C. cocconeiformis f. elliptica which has larger areolae along the base of the mantle that continue around the margin of the valve and there are additional areolae scattered in the terminal area. The significance of these differences between C. kernii and C. cocconeiformis f. elliptica need further investigation. C. kernii also resembles the smaller valves of C. davisiae but easily differentiated by the small (versus large round in C. davisiae) central area, distal fissures not hooked (deflected in opposite direction in C. davisiae), sharp bend at the valve margin (versus more gently rounded in C. davisiae), and the lower stria density, (22–24 versus 26–32 in 10 µm in C. davisiae). Another similar taxon is C. thoroddsenii (Foged) Lange-Bertalot (see: Foged, 1974, fig. 17: 7–10). Cavinula kernii is differentiated by a smaller valve size (L=19–31 µm, W=11–13 µm in C. thoroddsenii), and the small rounded central area versus apically elongated central area in C. thoroddsenii. C. hilliardii (Figs 112–122) differs by the valve shape and the orientation of striae (for comparison also see Foged 1971, fig. 14: 18).

Distribution:— So far, this taxon (sensu stricto) was only observed in the samples from the type locality, Kern River, Kernville, California, USA. In July 1992, the pH was 8.4 with a specific conductance of 158 µS/cm.