Neidium tumescens

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 : 207-211

Neidium tumescens (Grunow in Schmidt 1877: pl. 49, fig. 10) Cleve (1894: 70) s. str., emend. K.Lefebvre &

P.B.Hamilton ( Fig. 22 )

Basionym : Navicula ( firma var.) tumescens Grunow in Schmidt, Atlas der Diatomaceen-kunde. Aschersleben, Commissions-Verlag Von Ludwig Siever’s Buchandlung, fig. 49: 10. 1877.

Emended species description (individuals examined for morphological analyses: 15, examined for molecular analyses: 2): Valves are broadly lanceolate to elliptical with narrowly rostrate to attenuated ends ( Fig. 22 ). Valve length: 181–216 μm, width: 55–83 μm. Striae are weakly radiate at the centre changing to parallel and slightly convergent at the apices. The striae appear densely spaced, although individual stria and areola can be discerned in LM, 15–17 present in 10 μm. Voigt faults are present approximately ½ way from the margin of the central area to the apex on the secondary side of the valve. Areolae are more densely spaced closer to the axial area, 14–18 in 10 μm becoming less dense towards the valve margins 11–14 in 10 μm. Axial area is linear-elliptical from center to apex with the central area transapically expanded and rounded. Central area extends over 1/4 to 1/5 the valve width. Ten or more longitudinal canals are present along the sides of the valve. The first canal closest to the axial area is wider than other canals. In LM, the raphe appears filiform and linear-elliptical, in SEM the raphe is linear. The proximal raphe endings are tightly hooked and the distal ends terminate in a lacinia (bifurcate in appearance). Internally, the raphe is straight, the distal raphe ending forms a small helictoglossa positioned on the edge of a small silica plate at the apex. The proximal raphe fissures from the two raphe branches form narrow linear helictoglossae which are weakly connected by a fine silica ridge. Renilimbia are prominent on areolae along the axial area and the longitudinal canals. The areolae are chambered and interconnected along the striae.

Observations:— Neidium tumescens’ defining features are the very large number of canals (10+), as well as its unique shape and large size ( Fig. 22 , type locality). It is much more elliptical than other large species like N. amphigomphus ( Figs 26–30 ) or N. dilatatum ( Figs 23–24 ), with ends that are much more pinched. All the longitudinal canals internally have linear to linear-elliptical apertures ( Güttinger 1989). The first longitudinal canal is always larger and internally is raised as a small dome. The remaining longitudinal canals on the outside are flush with the valve face and internally are weakly raised. Areolae within the valve wall form a complex chambered network similar to N. dilatatum , N. amphigomphus , N. fossum , sp. nov. and N. hitchcockii . The central area helictoglossae are distinctly separated, but united by a fine silica ridge. Examples of N. tumescens in the literature include Patrick & Reimer (1966: 34, fig. 4), Metzeltin & Lange-Bertalot (2007: 180, figs 1–2), Camburn & Charles (2000: 22, fig. 4) and Güttinger (1989: 2.05.32- 1). One specimen was observed from fossil material collected at the type locality Cherryfield, Maine ( Fig. 22 ). This is a freshwater species found in acidic waters from eastern North America, not an Arctic species.

Neidium dilatatum ( Ehrenberg 1843: 418) Cleve (1894: 70) emend. K.Lefebvre & P.B.Hamilton ( Figs 16 , 23–24 , 35–38 )

Baysionym: Navicula dilatata Ehrenberg, Abhandlungen der Königlichen Akademie der Wissenschaften zu Berlin 1841: 418. 1843. Original figure: Ehrenberg, Mikrogeologie: pl. 3(II): 5, pl. 3(IV): 13, pl. 4(I): 5, pl. 4(II): 9, pl. 5(III): 1. 1854.

Emended species description (individuals examined for morphological analyses: 28, examined for molecular analyses: 6): Valves are elliptic-lanceolate with narrowing pointed apices ( Figs 23–24 ). Valve length: 174–269 μm, and width 40–55 μm. The axial area from center to apex is linear-elliptical. The central area is transapically elliptical, covering 1/2 to 1/3 the valve width ( Figs 23–24 ). The valve has many (5+) small longitudinal canals of even size along each margin ( Figs 23–24 ). In LM, the raphe appears filiform and linear-elliptical, in SEM the raphe is linear and the proximal ends tightly hook in opposite directions ( Figs 35–38 ). Striae are evenly spaced and weakly radiate at the centre becoming weakly convergent at the apices with 16–19 in 10 μm. One Voigt fault is clearly present half way between the centre and apex on the secondary side of the valve ( Figs 23–24 , 36–37 ). The areolae are small, fine rounded, and evenly spaced 14–18 in 10 μm. Externally in SEM the areolae are small round to elliptical and weakly recessed. Fine cribra are present within the areolae ( Figs 35–36 ). In LM the areolae appear as fine perforations ( Figs 23–24 ). Lacinia are clearly present externally ( Fig. 35 ). Internally, rounded elevated longitudinal canals are visible ( Fig. 38 ), and the fine rounded areolae are in tightly packed, evenly spaced striae ( Figs 37–38 ). In intact specimens the internal valve face is covered by a hymen. Renilimbia are present around areolae along the axial area and areolae opening into the longitudinal canals. Renilimbia are also present around randomly identified areolae on the internal valve face. The central helictoglossae are small elevated nodules close to the edge of the central area, they are weakly connected by a small fine silica ridge ( Fig. 38 arrow). The terminal helictoglossae are small and facing inward on a thickened apical nodule. Areolae form chambers within the valve wall and the chambers are interconnected along the striae (Supplemental Plate 2, Fig. d).

Type:— UNITED STATES OF AMERICA. Massachusetts: Andower, fossil, Prof. Bailey, ca. 1842, Ehrenberg Sample no. 1771 (lectotype designated here: BHUPM! ECO-101, isolectotype: circled specimen illustrated here as Fig. 16 ).

Observations:— Neidium dilatatum was recorded from 10 localities in Ehrenberg’s original work including living and fossil materials ( Figs 1–3, 9–15 ). All the drawings show a large linear-elliptical to elliptical valve with narrowly rounded almost apiculate apices. N. dilatatum was also shown to be larger than N. amphigomphus ( Figs 1–3 ). In eight of the drawings, multiple lines were presented along the valve margins ( Figs 1–3, 10–13, 15 ). In nine of the drawings round-elliptical central areas were drawn ( Figs 1–3, 9–12, 14–15 ). Specimens examined from Ehrenberg’s mica collection confirm the general morphological features described above (Supplemental Plate 1). However, size differences for specimens were observed between sites. The smaller valves ( Figs 9, 13, 14 ) <160 μm, from Stratford, West Port and Wrentham, also appear to have one larger longitudinal canal along the margin with associated smaller canals (see Supplemental Plate 1, Figs m–q). LM and SEM examination of possible syntype material from West Point, and Stratford confirm smaller valves with one larger longitudinal canal. In contrast the larger linear-elliptical valves (>150 μm) have many longitudinal canals of more or less the same size. Further, the smaller valves have the same size range as N. amphigomphus . Based on direct comparisons of valve size between N. amphigomphus and N. dilatatum , from Andower (Supplemental Plate 2), Boston and Bridgewater, and large valves observed from Pelham, Smithfield and Blue Hill, N. dilatatum sensu stricto is a large linear-elliptical valve with multiple longitudinal canals of even size. The size ranges for observed Ehrenberg samples were length 164–264 μm, width 39–56 μm, and 14–17 striae in 10 μm. In the past, this taxon has not been identified and used in the common taxonomic literature.

Specimens of N. dilatatum were commonly identified as N. iridis sensu auct. or sometimes N. amphigomphus sensu auct. nonnull. An example can be found in Krammer & Lange-Bertalot (1986: 104, figs 1, 4). Specimens identified as N. iridis sensu auct. nonnull. ( Camburn & Charles 2000: 21, fig. 1; Metzeltin & Lange-Bertalot 2007: 179, figs 3–5) are likely to also be N. dilatatum , given the large size range of the specimen. At the smaller end of the size range N. dilatatum can be confused with N. amphigomphus , but comparisons of the shapes and sizes of the areolae from centre to valve margin (becoming larger in N. amphigomphus ) and central area (small round in N. amphigomphus ) can assist in distinguishing the two taxa. Metzeltin & Lange-Bertalot (2007: 183, figs 1–4) show fossil specimens identified as N. amphigomphus from Florida which fit some of the characteristics of N. dilatatum such as overall shape, and areola density. However, the smaller size (118–171 μm) of these fossils falls below the extant size ranges we observed.

Within the samples analysed phylogenetically ( Table 1), N. dilatatum was long and narrow with straight to mildly elliptical sides. Based on genetic analysis, there is a large range in valve size and over all morphology (Supplemental Plate 3, Figs l–q). The ends are narrowly rounded ( Figs 23–24 , 36–37 ), which was also seen with the valves of N. fossum , sp. nov. ( Figs 31–34 , 44, 46–47 ) compared to the apiculate ends of N. amphigomphus ( Figs 40, 42 ). N. dilatatum was larger than N. fossum ( Figs 31–34 , 47 ), with a rounder central area, and very tightly hooked proximal raphe ends ( Figs 35, 38 ). Five or more evenly sized longitudinal canals are present in N. dilatatum ( Fig. 35 ) compared to N. fossum with a single large canal (Supplemental Plate 2, Fig. f, arrow) and numerous small canals ( Figs 43, 45, 47 , Supplemental Plate 2, Fig. f).

Neidium dilatatum appears to be globally distributed.

Figures

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 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 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 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 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.