Neidium amphigomphus ( Ehrenberg 1843: 417 ) Pfitzer (1871: 39) emend. K.Lefebvre & P.B.Hamilton

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 : 213-214

Neidium amphigomphus ( Ehrenberg 1843: 417) Pfitzer (1871: 39) emend. K.Lefebvre & P.B.Hamilton ( Figs 17 ,

26–30 , 39–42 )

Basionym : Navicula amphigomphus Ehrenberg, Abhandlungen der Königlichen Akademis der Wissenschaften zu Berlin 1841: 417. 1843.

Original figure: Ehrenberg, Mikrogeologie: pl. 2(II): 11, pl. 2(III): 8a, pl. 3(I): 6, pl. 3(II): 6, pl. 3(IV): 12, pl. 4(I): 6, pl. 4(III): 3, pl. 5(III): 15. 1854.

Emended species description (individuals examined for morphological analyses: 45, examined for molecular analyses: 11): Valves are linear to linear-elliptic with acute rounded apices ( Figs 26–30 ). Valve length 73–141 μm, and width 23–38 μm. Axial area from center to apex linear to linear-elliptical. Central area is round to elliptical covering approximately 1/3 of the valve width ( Figs 17 , 39, 41 ). In LM, the raphe appears filiform and linear-elliptical, in SEM the raphe is linear. The proximal ends form small hooks in opposite directions and the distal raphe ends form a lacinia ( Fig. 40 ). Striae are parallel to mildly oblique and loosely packed 15–19 in 10 μm. The areolae are large and regularly spaced, smaller and rounded areolae closer to the axial area, becoming larger and more elliptical towards the valve mantle with 14–20 in 10 μm ( Figs 39–40 ). In SEM, externally the areolae form depressions with smaller opening in the center which may or may not be occluded with cribra ( Figs 39, 40 , Siver et al. 2005, pl. 50, figs 2–3). 3–5 longitudinal canals are visible ( Fig. 40 ). Internally, the longitudinal canals are less evident ( Fig. 41 ) and areolae are positioned within surface depressions and barely visible under the hymen in intact valves ( Figs 41–42 ). The terminal helictoglossae form small thickened nodules close to the apex. Renilimbia are positioned around areolae across the valve face ( Figs 41–42 , Siver et al. 2005, pl. 50, figs 5–6). The valve wall is chambered and the areolae are internally interconnected both apically and transapically. Each proximal helictoglossa forms a thickened nodule on top of the central nodule and are weakly connected by a small silica ridge ( Fig. 41 ). In combination, the proximal helictoglossae are not aligned ( Fig. 41 , Siver et al. 2005, pl. 50, Fig. 4 ). The terminal helictoglossae form small thickened nodules close to the apex ( Fig. 42 ).

Type:— UNITED STATES OF AMERICA. Massachusetts:Andower, fossil, Prof. Bailey, ca. 1842, Ehrenberg sample no. 1771 (lectotype designated here: BHUPM! ECO-100, circled specimen illustrated here as Fig. 17 ).

Observations: Neidium amphigomphus was identified from eight localities in Ehrenberg’s original work ( Figs 1–8 ). All line drawings show valves with linear sides and apiculate apices. In six of the eight drawings, multiple lines are presented along the valve margins suggesting some type of unique valve formation ( Figs 1–3, 4, 6–7 ). The line drawings from Bridgewater, Andower and Boston clearly show that N. amphigomphus is smaller than N. dilatatum . Specimens observed from the micas also illustrate valves with linear margins and apiculate apices. (Supplemental Plate 1, Figs e–h). Shadowing along the margins was also observed on some of the mica specimens (Supplemental Plate 1, Figs e–f). In the current LM study, nine intact specimens from the type material showing multiple longitudinal canals were observed, and one from Bridgewater (Massachusetts) was selected as the lectotype ( Fig. 17 ). The size ranges for observed specimens from Ehrenberg’s collection were length 106–167 μm, width 26–42 μm, and 14–16 striae in 10 μm. This taxon has been commonly identified under many different concepts with only a few identifications representing N. amphigomphus sensu stricto. Examples of N. amphigomphus sensu stricto include Patrick & Reimer (1966: 34, fig. 2) and Siver et al. (2005: 49, figs 1–4, 50, figs 1–6). No specimens of N. amphigomphus were presented in Kramer & Lange-Bertalot (1986).

Within the specimens of N. amphigomphus sequenced and analysed phylogenetically, two key characteristics were evident. One, the distinct acute and apiculate apices of the valve and two, the areolae tend to become larger and more linear towards longitudinal canals ( Figs 40, 42 ). This is in contrast to the smaller rounded areolae of N. dilatatum ( Figs 23–24 , 35, 37 ) and N. fossum ( Figs 31–34 , 44–45, 47 ). Neidium amphigomphus also has a circular central area, with 3–5 longitudinal canals ( Figs 39–42 ) which contrasts with the broad central area and broad longitudinal canal with associated smaller canals in N. fossum ( Figs 43–47 ).

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 26–34. 26–30. Neidium amphigomphus. LM external view illustrating the size range of the valve. Note the straight pointed ends, small elliptical central area, and tight proximal raphe ends. 26. From CANA 93650. 27. From CANA 93279. 28. From CANA 93284. 29. From CANA 100066. 30. From CANA 100072. 31–34. Neidium fossum from CANA 100072. LM external view illustrating the size range of the valve. Note the large inner-most canal and subsequent small canals, arrow shaped ends, ovular central area and bent proximal raphe ends. 33. Neidium fossum holotype (CANA! 100072). Scale bar = 20 μm.

FIGURES 35–42. 35–36. Neidium dilatatum from CANA 93284. SEM external view of apex and central area, note tight circular central area, multiple small canals and small hooked proximal raphe ends. 37–38. Neidium dilatatum from CANA 100072. SEM internal view of apex and central area, note arrow-shaped ends with multiple small canals. Arrow indicates the fine silica ridge connecting the central helictoglossae. 39–40. Neidium amphigomphus from CANA 93284. SEM external view of apex and central area, note oblong central area and equal triangular ends. 41–42. Neidium amphigomphus from CANA 100072. SEM internal view of apex and central area, note the parallel sides and the equal triangular ends. Scale bars = 10 μm (39–42), 20 μm (35–38).

FIGURES 1–15. Extracted from Ehrenberg’s original line drawing (ECD). 1b, 2a, 3a, 4–8. Identified as Navicula amphigomphus. 1b. ECD2239 Andower.2a. ECD2238 Boston. 3a. ECDR2241 Bridgewater. 4. ECD2068 Rel del Monte.5. ECD2233 West Point.6. ECD2247 Blue Hill Pond II. 7. ECD2246 Blue Hill Pond I. 8. ECD2234 Stratford. 1a, 2b, 3b, 9–15. Identified as Navicula dilatatum. 1a. ECD2239 Andower. 2b. ECD2238 Boston. 3b. ECD2241 Bridgewater. 9. ECD2233 West Point. 10. ECD2236 Smithfield. 11. ECD2237 Pelham. 12. ECD2247 Blue Hill Pond II. 13. ECD2234 Stratford. 14. ECD2243 Wrenham. 15. ECD2246 Blue Hill Pond I. Reproduction of these images under the copyright permission of the Institute of Paleontology, Museum für Naturkunde, Humboldt University of Berlin (BHUPM).

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.

FIGURES 43–47. 43–44. Neidium fossum from CANA 100072. SEM external view of apex and central area, note ovular central area, large internal canal with smaller external canals, and long bent proximal raphe ends. 45–46. Neidium fossum from CANA 100072. SEM internal view of apex and central area. Note large internal canal. 47. Neidium fossum from CANA 100072. SEM internal view of whole valve. Note the large internal canal and oblong central area. Scale bar = 10 μm.