Neidium fossum K.Lefebvre & P.B.Hamilton, 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 : 214-215

publication ID

https://doi.org/ 10.11646/phytotaxa.220.3.1

persistent identifier

https://treatment.plazi.org/id/7404878E-0910-7415-8988-F9E6DA8CFF4B

treatment provided by

Felipe

scientific name

Neidium fossum K.Lefebvre & P.B.Hamilton
status

sp. nov.

Neidium fossum K.Lefebvre & P.B.Hamilton , sp. nov. ( Figs 18, 20 View FIGURES 16–21 , 31–34 View FIGURES 26–34 , 43–47 View FIGURES 43–47 )

Individuals examined for morphological analyses: 27, examined for molecular analyses: 1. Valves are elliptic-lanceolate, with narrowing to subacute apices ( Figs 31–34 View FIGURES 26–34 ). Valve length 92–142 μm and width 22.5–34.0 μm. Central area is transapically broad and elliptical, covering 1/3 to 1/2 the valve width. The axial area from centre to apex is linear-elliptical. In LM, the raphe appears filiform and linear-elliptical, in SEM the raphe is linear. Proximal ends form hooks in opposite directions and the distal raphe ends form a lacinia ( Figs 43–47 View FIGURES 43–47 ). Striae are parallel and moderately spaced becoming weakly convergent towards the apices, 17–21 in 10 μm. Voigt faults are present on the secondary side of the valve. Areolae are regularly spaced and irregular in shape, 17–20 in 10 μm. In SEM, externally the areolae are flat to the valve surface sometimes with cribra occlusions and not in deep depressions ( Figs 43–44 View FIGURES 43–47 ). Internally, the areolae are positioned within small depressions ( Fig. 47 View FIGURES 43–47 ). One large longitudinal canal is present along each valve margin ( Figs 43–47 View FIGURES 43–47 ). Additional canals 2–3 or more may extend along the valve mantle. Externally the longitudinal canal is flat with the valve face ( Fig. 43 View FIGURES 43–47 ), internally the canal forms a bulge along the valve margin ( Fig. 46 View FIGURES 43–47 ). A single row of linear to linear-elliptical areolae open externally and internally from the canal ( Figs 45–46 View FIGURES 43–47 ). Internally, areolae are covered by a hymen ( Fig. 45 View FIGURES 43–47 ). Renilimbia are positioned around areolae along the axial area, and the region of the longitudinal canals ( Figs 45–46 View FIGURES 43–47 ). Renilimbia can also be found randomly scattered around areolae on the valve face. Areolae form chambers in the valve wall that are highly interconnected transapically ( Fig. 47 View FIGURES 43–47 , Supplemental Plate 2, Fig. f). Each proximal helictoglossa forms a double elevated ribbed nodule that is loosely connected to the adjacent helictoglossa by a thin ridge of silica ( Figs 45, 47 View FIGURES 43–47 ). The terminal helictoglossae form on small thickened nodules close to the apex ( Figs 46, 47 View FIGURES 43–47 ).

Type:— UNITED STATES OF AMERICA. New York: Adirondack Park, K. Lefebvre, 5 May 2014 (holotype: CANA! 100072, circled specimen, illustrated here as Fig. 33 View FIGURES 26–34 ).

Etymology:—The specific epithet ( fossum ), Latin meaning ditch, trench or canal, refers to the large longitudinal canal seen in N. fossum

Observations: — Neidium fossum was identified from four of Ehrenberg’s samples, (Andower MA, Bridgewater MA, Pelham MA and Stratford CT), where it had been listed under either N. dilatatum or N. amphigomphus ( Figs 18, 20 View FIGURES 16–21 , Supplemental plate 2). From the Ehrenberg samples, the size ranges of N. fossum observed were length: 90–158 μm, width: 22–40 μm and 19–26 striae in 10 μm. Within the modern samples observed in the phylogenetic study, N. fossum ( Figs 31–34 View FIGURES 26–34 ) has a similar overall shape to N. dilatatum ( Figs 23–24 View FIGURES 22–25 ), however N. fossum is much smaller than N. dilatatum with a maximum length of 160 μm. This species can be differentiated from N. amphigomphus , by its narrowly rounded ends, and longitudinal canal structure of one large and several small canals ( Figs 43–47 View FIGURES 43–47 ). It can be differentiated from N. dilatatum ( Figs 35–38 View FIGURES 35–42 ) with its large longitudinal canal, smaller overall size, more transapically elliptical central area and its straight bifurcating terminal raphe ends ( Figs 43, 46 View FIGURES 43–47 ). There is taxonomic confusion around large linear-elliptical Neidium taxa with multiple longitudinal canals extending along the valve margins. One clade which is represented by one larger canal with associated smaller canals, can be linked to N. fossum . Specimens identified as Neidium iridis sensu auct nonull.— Camburn & Charles (2000: 21, fig. 2), Metzeltin & Lange-Bertalot (2009: 93, figs 1–4, 94, figs 1–9)—and as Neidium amphigomphus —Metzetlin & Lange-Bertalot (2002: 51, fig. 1), Metzeltin & Lange-Bertalot (2007: 183, fig. 5, 188, fig. 3, 189, fig. 2), Metzeltin & Lange-Bertalot (2009: 95, figs. 1–3)—are N. fossum or closely related undescribed cryptic species. Other similar specimens identified under N. iridis include Patrick & Reimer (1966: 34, fig. 1) and Krammer & Lange-Bertalot (1986: 104, fig. 2).

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