Neidium firmum ( Kützing 1844: 92 ) P.B.Hamilton & K.Lefebvre 2015

Lefebvre, Keely E. & Hamilton, Paul B., 2015, Morphology and molecular studies on large Neidium species (Bacillariophyta) of North America, including an examination of Ehrenberg’s types, Phytotaxa 220 (3), pp. 201-223 : 211-213

Neidium firmum ( Kützing 1844: 92) P.B.Hamilton & K.Lefebvre , comb. nov. et emend. ( Fig. 21 )

Basionym : Navicula firma Kützing, Bacillarien oder Diatomeen 92, fig. 21: 10. 1844.

Emended species description (individuals examined for morphological analyses: 1, examined for molecular analyses: not available): Valve is linear-elliptical with narrow rounded apices ( Fig. 21 ). Valve length 79 μm, and width 16–17 μm. The axial area from centre to apex covering ca. 1/6 of the valve width. The central area is broad, transapically elliptical, covering 1/2 the valve width. The valve has 1, possibly up to 3 longitudinal canals of even size along each margin. In LM, the raphe appears filiform and linear-elliptical with broadly curved and deflected proximal raphe ends and terminal raphe end forms a lacinia. Striae are weakly radiate at the centre becoming weakly convergent at the apices with 17 in 10 μm. Voigt faults are present on the secondary side of the valve. The areolae are large, round to elliptical, and evenly spaced 10–11 in 10 μm. In LM, the presence of a small pore in the center of the areolae ( Fig. 21 , arrow) suggests that the areolae are within surface depressions on the valve face.

Type:— ITALY. Grosseto: San Fiore, fossil, ca. 1840, BM! 18414 (lectotype designated here: individual at microscope coordinates from the center of the type sticker over to the microscope coverslip x = - 17.49 mm, y = - 2.27 mm, illustrated here as Fig. 21 ).

Observations: Only one large Neidium valve was found on the type slide which is here shown as Navicula affine var. firma . The slide was not the original examined by Kützing, but made later from original material. The valve does not exactly match the line drawing by Kützing (1844: 21, fig. 10). The overall length matches but the line drawing presents a valve with a length to width ratio of 4:1 while the observed specimen is 5:1. In addition, the central area in the line drawing is round covering over 1/3 the valve width while the central area on the valve from the type slide is elliptical and covers 1/2 the valve width. However based on the linear lines along the margin, there appears to be only one or a couple of longitudinal canals, which agrees with the valve presented. Since this slide was the only slide from San Fiore in Kutzing’s slide collection (D.M. Williams, pers. comm.), we conclude that the observed Neidium specimen should represent the species and is here identified as the lectotype.

Neidium hitchcockii ( Ehrenberg 1843: 418) Cleve (1984: 69) emend. K.Lefebvre & P.B.Hamilton ( Figs 19 , 25 ) Basionym : Navicula hitchcockii Ehrenberg, Abhandlungen der Königlichen Akademis der Wissenschaften zu Berlin 1841: 418. 1843. Original figure: Ehrenberg, Mikrogeologie: pl. 5(III): 11. 1854.

Emended species description (individuals examined for morphological analyses: 96, examined for molecular analyses: 1): Valves are linear with triundulate margins, the ends narrow sharply forming rostrate apices ( Fig. 25 ). Valve length: 62–85 μm, width: 14–22 μm. The axial area is broad, linear and centrally expanded. In SEM, the axial area is elevated and separated from the valve face by a thickened conopeum-like ridge ( Hamilton et al. 1995: figs 14, 17, 18). Small fine poroids are present in the axial area. The central area is small and elliptical, slightly expanded from the axial area. In LM, the raphe appears filiform and linear-elliptical, in SEM the raphe is linear and the proximal ends are long and deflected (not curved) into the central area. Sometimes the terminal end of the proximal raphe fissure is forked ( Hamilton et al. 1995: fig. 17). The striae are weakly radiate at the centre to weakly convergent at the apices, 19–22 in 10 um. Areolae are large and rounded, 20–24 in 10 μm. In SEM, externally the areolae opening are occluded by fine subsurface cribra ( Hamilton et al. 1995: fig. 17). Internally, the areolae are positioned with broad surface depressions (Supplemental Plate 2). In intact specimens, the internal valve face is covered by a hymen. One large, elevated, longitudinal canal is present along each margin. The canals have some or no poroid openings to the external valve face. In SEM, internally the longitudinal canal is at the edge of the valve face mantle junction with elliptical (not round) openings (Supplemental Plate 2). Renilimbia are present around areolae along the axial area and areolae opening into the longitudinal canals ( Hamilton et al. 1995: fig. 17). Renilimbia are also found around random areolae on the internal valve face. The central helictoglossae are present on a transapically raised central nodule and form two distinct nodular thickenings weakly connected by a small ridge of silica (Supplemental Plate 2). The terminal helictoglossae are small and facing inward on a thickened apical nodule (Supplemental Plate 2). The valve wall is chambered, areolae interconnected primarily along the striae and into the longitudinal canal ( Hamilton et al. 1995: figs 19, 21). Copulae (3–4) have one to two rows of poroids along the par exterior.

Type:— UNITED STATES OF AMERICA. Massachusetts: Bridgewater, peat material, Prof. Hitchcock, ca. 1842, Ehrenberg sample no. 1769 (lectotype designated here: BHUPM! ECO-102, circled specimen, illustrated here as Fig. 19 ).

Observations: Neidium hitchcockii was first recorded by Ehrenberg from Bridgewater Massachusetts ( Fig. 19 ). The distinctive morphological shape along with size can distinguish this taxon in Ehrenberg’s original line drawings and the micas (Supplemental Plate 1, Figs a–d). A more recent LM and SEM study of N. hitchcockii ( Hamilton et al. 1995) shows distinct deflected central raphe ending sometimes forked, an elevated axial region extending from apex to apex, renilimbia around the areolae, and the presence of lacinia. These characteristics were also seen in specimens from the N. hitchcockii sample, which was sequenced ( Fig. 25 , SI 3 Fig. t). A few specimens were observed from type material and one individual has been selected as the lectotype ( Fig. 19 ). Size ranges for the observed individuals were length 46–80 μm, width 14–19 μm, and 18–21 striae in 10 μm. Positive identifications of this taxon include Patrick & Reimer 1966 (pl. 36: 2), Krammer & Lange-Bertalot (1986: 107, fig. 3), Hamilton et al. (1995: figs 1, 8–24), and Camburn & Charles (2000: 20, fig. 26). More complete comparisons with Neidium baicalense Jasnitsky (1936: 693) and N. sauramoi Mölder (1937: 30) are still required. At present, N. hitchcockii is considered to be very widespread (North America eastern and western regions, Europe, Asia, Australia & New Zealand).

Figures

FIGURES 16–21. Neidium specimens (LM) original type materials. 16. Neidium dilatatum lectotype,Andower Massachusetts (BHUPM! ECO–101). 17. Neidium amphigomphus lectotype, Bridgewater Massachusetts (BHUPM! ECO–100). 18. Neidium fossum originally identified by Ehrenberg as N. dilatatum, Stratford Connecticut. 19. Neidium hitchcockii lectotype, Bridgewater (BHUPM! ECO–102). 20. Neidium fossum originally identified by Ehrenberg as N. dilatatum, Pelham Massachusetts. 21. Neidium firma lectotype (BM! 18414). Scale bar = 20 μm.

FIGURES 22–25. 22. Neidium tumescens from Cherryfield, Maine. LM external view illustrating the whole valve. 23–24. Neidium dilatatum. LM external view illustrating the size range. 23. From CANA 93279. 24. From CANA 93281. 25. Neidium hitchcockii from CANA 100068. LM external view illustrating the whole valve. Scale bar = 20 μm.