Navicula subwalkeri Bahls & Potapova, 2015

Bahls, Loren & Potapova, Marina, 2015, Two new species of Navicula (Bacillariophyta, Naviculales) from the Cascade Mountains of the American Northwest, Phytotaxa 218 (3), pp. 253-267 : 260

Navicula subwalkeri Bahls & Potapova , sp. nov. ( Figs 34–52 )

Valves lanceolate with subrostrate apices. Length 101–165 μm, width 17–27 μm. Valve face convex in transapical plane, gradually merging with the mantle. Axial area narrow, widening gradually from apices to central area. Central area small, rhombic. Raphe lateral and slightly bowed, concave to the primary side. Proximal raphe ends inflated and bent towards the secondary side. Distal raphe ends shaped like question marks. Striae radiate, becoming parallel, then convergent near the apices, 8–11 in 10 μm. Striae curved, alternately long and short around central area. Internally, striae partially covered by axial plate. Edges of axial plate visible in LM as longitudinal lines at about one-third distance from axial area to valve margin. Areolae apically elongated, 22–26 in 10 μm. Cells solitary with two plate-like chloroplasts lying along the girdle on each side of the valve.

Type:— USA. Oregon, Douglas County: North Umpqua River, 43.311º N, 122.155º W, 1262 m a.s.l., A. Johnson , 5 August 2011 (holotype: circled specimen on ANSP! GC 65222, illustrated in Fig. 34 . Isotypes: circled specimens on MONTU! 41-100, MDC! 126-94. Paratypes: MONTU! 11-51, MDC! T-3-14-18).

Etymology:—This species is named for its appearance as a smaller version of Navicula walkeri .

Distribution: —Clearwater and North Umpqua Rivers, Oregon; fossil in Pliocene diatomite near Chiloquin, Oregon (ANSP! GC63230, Fig. 43 ) (slide GC63230 was deposited at ANSP by A.D. Mahood and was made from the Chiloquin diatomite sample N 1020 collected in 1978 by E.P Jones; see Mahood (1981)).

Observations:— Navicula subwalkeri has frustular morphology so far described only for N. walkeri and N. jakovljevicii . All three species have an internal axial plate partially occluding the striae, with its edges visible as longitudinal lines on both sides of the axial area. N. subwalkeri is most similar to N. walkeri ( Figs 53–70 ), but is distinguished from it by its narrower valves and axial plate, protracted apices, smaller central area, curved striae, and higher density of areolae ( Table 3). Since the axial plate in N. subwalkeri is narrower than in N. walkeri , the longitudinal lines visible in LM are closer to the axial area; in N. walkeri they are closer to the valve margins ( Bahls 2011d, Kociolek et al. 1998). Another difference between the two species is the absence of marginal lamina in N. subwalkeri ( Figs 50, 51 ) and their presence in N. walkeri ( Figs 68, 69 ). Raphe structure is similar in both species: an uninterrupted internal slit ( Figs 52 , 70 ) and large terminal nodules ( Figs 51 , 69 ), although the proximal raphe ends of N. subwalkeri are smaller and not as strongly bent to one side as those of N. walkeri ( Figs 47, 49 , 65, 67 ). Although the two species are sympatric, N. walkeri has a much wider distribution than N. subwalkeri ( Table 2).

Figures

FIGURES 34–46. Navicula subwalkeri, LM. 34. Holotype specimen. 42. Close-up of central area. 45, 46. Preserved specimens with intact but somewhat degraded chloroplasts. 34, 37, 41, 45, 46. North Umpqua River, Oregon. 35, 36, 38–40, 42, 44. Clearwater River, Oregon. 43. Pliocene diatomite, Chiloquin, Oregon (ANSP! GC63230). Scale bars: Fig. 42 = 5 μm; all others = 10 μm.

FIGURES 47–52. Navicula subwalkeri, SEM, North Umpqua River, Oregon. 47–49. External valve views. 50–52. Internal valve views. Scale bars: Figs 47, 50 = 10 μm; all others = 2 μm.

FIGURES 53–64. Navicula walkeri, LM. 60. Close-up of central area of valve in 63. 61, 62. Iconotypes, Sovereign 1958. 63, 64. Same valve at different levels of focus. 53. North Umpqua River, Oregon. 54, 55, 57–59. Snow Creek, Oregon. 56. Pit River diatomite, California (ANSP! Boyer 338). 60, 63, 64. Lake Creek, Oregon.

FIGURES 65–70. Navicula walkeri, SEM. Snow Creek, Oregon. 65–67. External valve views. 68–70. Internal valve views. Scale bars: Figs 65, 68 = 10 μm; all others = 5 μm.