Cavinula lapidosa Mann, sensu lato

Cavinula lapidosa (Krasske) Mann sensu lato (Figs 125, 126)

Basionym: Navicula lapidosa Krasske 1929: 354, 7

Valves elliptical, with narrowing rounded apices. Valve length 13–18 µm, width 6–7 µm. Striae punctate, parallel to weakly radiate at the apices, 18–24 in 10 µm (measurements from Krasske material). Striae radiate throughout, curved at center and straight at apices. Areolae round barely visible in LM, 20–25 in 10 um. Axial area narrow linear, central area a bow-tie fascia with shortened striae along the margins. Raphe broad, linear; proximal fissures expanded, distal fissures deflect to opposite sides of the valve.

Syntypes: –– Sachsen, Hessen (Germany), Chile. Lange-Bertalot et al. 1996, fig. 19: 22–26 (syntype).

Observations:— In the original description three syntype localities were identified from Germany and Chile. The original line drawing illustrates an elliptic lanceolate valve with straight striae and a narrow raphe (morphotype 1, from Germany) while the LM images in Lange-Bertalot et al. (1996) from Chile are more elliptical with curved striae and a broader raphe with distinct proximal raphe fissures (morphotype 2). There appears to be either a broad variation in valve form or more likely different taxa. The specimen from Krasske’s material near Hessen, Germany, deposited at BRM N14/87a (Fig. 126) matches morphotype 1, while specimens from the southern USA (Fig. 125) more closely match morphotype 2. Cavinula lapidosa sensu lato is distinguished by the straight raphe with deflected terminal raphe fissures, the strongly radiate striae from center to apex and the bow-tie shaped central area with short striae of varying length along the margins. C. lapidosa can be compared to C. weinzierlii (Schimanski) Czarnecki, but is distinguished by bow-tie shaped central area, areolae formation, and the position of the proximal raphe fissure at the edge of the central area (compared to in the center of the central area in C. weinzierlii).

Distribution:— Two records for C. lapidosa were reported in the CANA database from Ellef Ringnes Island and Axel Heiberg Island Arctic Archipelago. These specimens match morphotype 1 with an elliptic lanceolate valve and broad bow-tie shaped central fascia. In the ANSP collection, 16 sites from across the USA were identified to have C. lapidosa. The sites in the southern USA are linked to morphotype 2. As currently documented, this taxon has a wide latitudinal distribution from the north and southern hemispheres, more specifically across all of North America.

Distribution Records:— Lange-Bertalot et al. (1996, fig. 19: 22–26, syntype, Chile), Krammer & Lange-Bertalot (1986, fig. 73: 5, 6, Europe).