Cavinula davisiae Bahls, 2013

Bahls, Loren, 2013, New diatoms (Bacillariophyta) from western North America, Phytotaxa 82 (1), pp. 7-28 : 15-16

Cavinula davisiae Bahls , sp. nov. ( Figs 43–51 )

Valves elliptic-lanceolate with broadly rounded apices. Valve length 14–31 µm; valve width 7.5–9.9 µm. Axial area narrow and linear; central area orbicular and large, about 1/2 valve width. Raphe filiform and straight with distinctly expanded proximal ends. Terminal raphe fissures hooked abruptly in opposite directions some distance from each apex. Striae radiate throughout, alternately long and short around the central area, 26–32 in 10 µm. Areolae round, 26–35 in 10 µm. Areolae of striae adjacent to central area larger and somewhat elongate transapically. Internally, proximal raphe ends T-shaped and areolae occluded by hymenes.

Holotype: — USA, Washington: Pierce County, Mount Rainier National Park, Clover Lake , 46.9289 o N, 121.5925 o W, elev. 1750 m, coll. R. Davis, 18 August 2012. MDC sample 496201; holotype slide MDC 41-56 ( Figs 43–51 ) (circled holotype specimen in Fig. 48 ). MONTU!

Isotypes: —MDC slide 126-50 ( MONTU!); circled specimens on ANSP! GC 65165.

Reported as: — Navicula variostriata ( Hein 1990: 76, pl. 31, figs 7–9); Navicula cf. variostriata ( Pienitz et al. 2003: 47, pl. 14, fig. 6).

Etymology:—This species is named after Ryan Davis, volunteer with Adventurers and Scientists for Conservation and collector of the holotype sample.

Observations:—Under SEM ( Fig. 50 ), the terminal raphe ends are shown to be hooked in opposite directions well short of the apices. Internally ( Fig. 51 ), with some additional magnification, the proximal raphe ends may be seen as T-shaped. Cavinula variostriata (Krasske) D.G. Mann in Round et al. (1990: 665) has more linear valves and an even larger central area. The central area of Navicula lapidosa Krasske (1929: 354) is shaped like a bow tie, not rounded.

Distribution and Ecology: — Cavinula davisiae appears to be endemic to the Pacific Northwest, where it is widespread and locally common in circumneutral waters with low conductivity. Previously, this species had been confused with Navicula variostriata Krasske (1923: 197) . Hein (1990) reported it from Adak Island, Alaska and Pienitz et al. (2003) reported it from islands off the Pacific Coast of western British Columbia.

Family Neidiaceae Mereschkowsky 1903: 127

Genus Neidium E. Pfitzer 1871: 39

Figures

FIGURES 43–51: Cavinula davisiae from Clover Lake, Mount Rainier National Park, Washington (type locality). Figs 43–49: LM images. Fig. 48: Holotype specimen. Figs 50, 51: SEM images. Fig. 50: External valve view showing distal raphe ends hooked in opposite directions well short of the apices. Fig. 51: Internal valve view showing (with some additional magnification) T-shaped proximal raphe ends. Scale bars: 10 µm.