Navicula trilatera Bahls, 2013

Bahls, Loren, 2013, New diatoms (Bacillariophyta) from western North America, Phytotaxa 82 (1), pp. 7-28 : 20-21

Navicula trilatera Bahls , sp. nov. ( Figs 76–84 )

Valves linear-lanceolate with subrostrate apices. Valve length 17.6–26.3 µm; valve width 4.5–5.5 µm. Axial area very narrow, widens into a moderately large but irregular central area. Raphe filiform with weakly expanded and widely spaced proximal ends. Terminal raphe fissures shaped like question marks. Striae radiate near the valve center, convergent toward the apices, 15–17 in 10 µm. Striae in the central area irregularly shortened or missing. Areolae about 40 in 10 µm.

Holotype:— CANADA, Alberta: Waterton Lakes National Park , Blakiston Beaver Pond A, 49.0928 o N, 113.8864 o W, elev. 1340 m, coll. B. Johnston, 2 June 2009. MDC sample 453301; holotype slide MDC 123-91 ( Figs 76–84 ) (circled holotype specimen in Fig. 78 ). MONTU!

Isotypes: —MDC slide 40-16 (MONTU!); ANSP GC 65091.

Paratypes: — USA, Montana: Stillwater County, Horseman Flat Lake , 45.4165 o N, 109.8716 o W, elev. 1646 m, coll. C. Levine, 14 September 1993. MDC sample 132901; MDC slide P3-12-19. MONTU !— USA, Montana: Flathead County, Glacier National Park, Camas Creek, 48.6233 o N, 114.0264 o W, elev. 1146 m, coll. Montana DEQ, 26 September 2006. MDC sample 404201; MDC slides 32-51, 116-50. MONTU !— CANADA, Alberta: Waterton Lakes National Park, Sofa Wetland A, 49.0656 o N, 113.7450 o W, elev. 1524 m, coll. B. Johnston, 5 June 2009. MDC sample 454001; MDC slides 40-23, 123-98. MONTU !— CANADA, Alberta: Waterton Lakes National Park, Sofa Mountain Ponds , 49.0333 o N, 113.7536 o W, elev. 2134 m, coll. B. Johnston, 27 July 2009. MDC sample 457001; MDC slides 40-53, 124-28. MONTU !

Etymology: —This species is named for its geographical distribution in headwaters on all three sides of the Continental Divide in the northern Rocky Mountains.

Observations: —Lineate striae and distal raphe fissures hooked to the same (secondary) side of the valve are evident externally under SEM ( Fig. 83 ). Internally, a thickened raphe sternum is present along with distal raphe ends that terminate in helictoglossae ( Fig. 84 ). Navicula veneta Kützing (1844: 95) has wedge-shaped apices and a smaller central area. Unlike N. trilatera , N. veneta is typically found in waters with elevated nutrients and dissolved solids. Navicula trilatera may be distinguished from N. longicephala Hustedt (1944: 277) , N. tenelloides Hustedt (1937: 269) , and N. vilaplanii Lange-Bertalot & Sabater in Rumrich et al. (2000: 173) by the shape and larger size of its central area. Navicula trilatera has the largest central area of all these Navicula species.

Distribution and Ecology: —In addition to the type locality, Navicula trilatera has been collected from two other wetlands in Waterton Lakes National Park, from Camas Creek on the west side of Glacier National Park, and from Horseman Flat Lake in the Beartooth Mountains of southern Montana (paratypes). These waters drain three sides of the Continental Divide: north to the Saskatchewan River, west to the Columbia River, and east to the Missouri River, respectively. Navicula trilatera prefers cool waters at higher elevations with somewhat alkaline pH and low conductivity.

Family Stauroneidaceae D.G. Mann in Round et al. 1990: 662

Genus Stauroneis C.G. Ehrenberg 1843: 45

Figures

FIGURES 69–84: Navicula supleeorum, Navicula trilatera. Figs 69–75: Navicula supleeorum from Rock Creek, Valley County, Montana (type locality). Fig. 72: Holotype specimen. Figs 76–84: Navicula trilatera from Blakiston Beaver Pond A, Waterton Lakes National Park, Alberta (type locality). Figs 76–82: LM images. Fig. 78: Holotype specimen. Figs 83, 84: SEM images. Fig. 83: External valve view showing lineate striae and distal raphe ends hooked toward the same (secondary) side of the valve. Fig. 84: Internal valve view showing thickened raphe sternum and distal raphe ends terminating in helictoglossae. Scale bars: Figs 69–82: 10 µm; Figs 83, 84: 5 µm.