Naviculonema stagnora Graeff, Kociolek & S.R. Rushforth, 2013

GRAEFF, C. L., KOCIOLEK, J. P. & RUSHFORTH, S. R., 2013, New and Interesting Diatoms (Bacillariophyta) from Blue Lake Warm Springs, Tooele County, Utah, Phytotaxa 153 (1), pp. 1-38 : 14-15

Naviculonema stagnora Graeff, Kociolek & S.R. Rushforth , sp. nov. ( Figs 64–75 ; figure 67 =

holotype)

Valves linear-elliptical without protracted apices, ends rounded ( Figs 64–69 ). Length 13.0– 31.5 µm, breadth 6.0– 7.5 µm. Axial area narrow, expanded to form an irregular central area ( Figs 64, 68 ). Striae around the central area coarser than others and not infrequently having the terminal areola isolated from others in the stria ( Fig. 64 ). Raphe filiform, straight, with external proximal ends dilated slightly ( Figs 65–67 ). External distal raphe ends deflected in the same direction ( Figs 64–67 ). The distinctly punctate striae are radiate for most of the length of the valve, becoming parallel ( Figs 64–65 ) or convergent ( Figs 67–68 ) at the ends. Individual striae are slightly curved, especially at the valve center. Striae 13–15/ 10 µm.

In the SEM, the valve exterior has a straight raphe with proximal ends that are not dilated ( Fig. 72 ), and distal ends that curve in the same direction onto the mantle ( Fig. 70 ). Striae are composed of areolae with siliceous flaps that give the openings a C or lunate shape ( Figs 71–72 ). In the central area there may be isolated areolae ( Fig. 72 ). Internally the areolae are round, and the external flaps are evident ( Fig. 74 ). The raphe is simple ( Fig. 73 ). Proximal raphe ends terminate at an undifferentiated central nodule ( Fig. 75 ). Distally the raphe ends form small helictoglossae ( Fig. 74 ). Isolated areolae in the central area do not appear to penetrate the interior of the valve.

Type: — USA. Blue Lake , Tooele Co., Utah. ( COLO 439035 , holotype (= Fig. 67 ), designated here; COLO 8506 , BM 101679, isotypes) .

Etymology: —Named for its presence in the lagoon-like main basin of Blue Lake.

Distribution:— Naviculonema stagnora is most common in the main basin of Blue Lake (COLO 8506).

Observations:—Kaczmarska & Rushforth (1983) identified Naviculonema stagnora as Navicula parva (Meneghini) Cleve-Euler (1953: 130 , figs 754 a–d, 756 g), but the line drawings of the taxon are inconclusive for identification of the taxon. Pankow (1976) lists the stria density of Navicula parva var. parva as 18–20/ 10 µm and provides an illustration of a specimen with very straight striae and raphe branches that are straight at the valve apices. There are no available SEM images of the taxon to confirm the form of the areola openings ( Henderson & Reimer 2003, Gaul et al. 1993). Parlibellus Cox (1988: 19) and Dickieia Berkeley ex Kützing (1844: 119) are two coastal genera that appear similar to Naviculonema stagnora in the LM, especially Dickieia with its irregular to barely X-shaped central area ( Witkowski et al. 2000: pls 103–108). According to Round et al. (1990: 516), Parlibellus has areolae that are “small round poroids occluded by hymenes,” while N. stagnora has external flaps. Cox (1985) provides SEM images and descriptions of two taxa that have since been transferred to Dickieia: Navicula subinflata Grunow in Cleve (1883: 470) and N. ulvacea (Berkeley) Cleve (1894: 129) . She describes the areolae of the taxa as “finely poroidal, having a simple external opening and an internal occlusion” ( Cox 1985). This description excludes Naviculonema stagnora from Dickieia. Our new genus also resembles Adlafia Moser et al. (1998: 87) . With regard to the genus as typified by A. muscora (Kociolek & de Reviers) Moser et al. (1998: 89) , Naviculonema has external flaps in the areolae versus hymenate occlusions, external distal raphe ends that are more rounded than strongly hooked, helictoglossae that are indistinct, and a central nodule that is distinct and bears internal proximal raphe ends that are straight (versus a small central nodule with raphe ends that are deflected in the same direction) ( Moser et al. 1998). In other groups of diatoms, the position (internal versus external) of the pore occlusions has helped to distinguish higher levels of taxonomic hierarchy, such as orders, family and genera ( Nikolaev & Harwood 2002, 2001).

Figures

FIGURES 64–69. LM. Naviculonema stagnora. Valve views showing the size diminution series. Figure 67 is the holotype. Scale bar: 10 µm.

FIGURES 70–72. SEM. Naviculonema stagnora. External valve views of two specimens. Fig. 70, Full external valve with distal raphe ends deflected in the same direction and irregularly-shaped central area. Fig. 71, C-shaped, occluded areolae. Fig 72, Straight proximal raphe ends and an isolated areola at the central area. Scale bars: Fig. 70: 5 µm; Figs 71–72: 1 µm.

FIGURES 73–75. SEM. Naviculonema stagnora. Internal valve views of two specimens. Fig. 73, Full internal valve view showing simple raphe. Fig. 74, Internal view of the siliceous covers over the areolae. Fig. 75, Specimen with an indistinct central area and flat central nodule. Scale bars: Fig. 73: 5 µm; Figs 74–75: 1 µm.