Characterization of a new species in the genus Didymosphenia and of Cymbella janischii (Bacillariophyta) from Connecticut, USA

Figures & data

Figs 1–6. LM images of field collected Didymosphenia hullii. Figs 1, 5, 6: Cells attached to their stalks illustrate cell division. Scale bars = 20 μm (Figs 1, 2, 5); 10 μm (Fig. 3); 50 μm (Fig. 4); 40 μm (Fig. 6).

Figs 7–15. LM images of Didymosphenia hullii cells in valve view showing size variation. Fig. 16: LM image of D. hullii cell in girdle view. Scale bars = 10 μm.

Figs 17–25. LM images of Didymosphenia geminata cells in valve view showing size variation. Fig. 17: Courtesy of S. Spaulding, Figs 18–24: Courtesy of D. Metzeltin. Reprinted from Metzeltin & Lange-Bertalot (2014, Iconographia Diatomologica 25) with the permission of Koeltz Scientific Books. Fig. 25: D. hullii cell in valve view. Scale bars = 10 μm.

Figs 26–28. SEM images of single valves of Didymosphenia hullii retrieved after PCR reactions. Fig. 26: The valve is fractured but still identifiable. Fig. 27: High magnification image of a cell with two stigmata. Scale bars = 20 μm (Figs 26, 28); 5 μm (Fig. 27).

Fig. 29. Bayesian phylogenetic tree based the V4 region of the 18S rDNA of selected published sequences of Cymbellales, plus newly obtained sequences from three isolated single cells of Didymosphenia sp. and four sequences of Cymbella janischii (GenBank accession numbers are included in the taxon labels). The current taxonomic families are indicated. Bayesian posterior probabilities (BPP × 100) values indicate node support. Scale bar = expected number of substitutions/site.

Figs 30–38. SEM images of Didymosphenia hullii on stalks from the West Branch of the Farmington River showing bifurcated stalks with cells attached. Scale bars = 20 µm (Figs 30, 31, 34); 50 µm (Figs 32, 33, 37); 40 µm (Fig. 35); 5 µm (Fig. 36); 200 µm (Fig. 38).

Figs 39–44. SEM images of Didymosphenia hullii. Fig. 39: Internal view of the valve displaying three stigmata. Fig. 40: View of apical pore field, footpole. Figs 41, 42: Central valve view with striae, and 1 and 4 stigmata, respectively. Fig. 43: Internal view of central valve showing two stigmata and uniseriate striae. Fig. 44: External views of frustule girdle and valve morphology. Scale bars = 20 μm (Fig. 39); 5 μm (Figs 40, 43); 10 μm (Figs 41, 42); 30 μm (Fig. 44).

Table 1. Comparison of traits of selected Didymosphenia taxa and their localities. Morphology of areolae determined using images and descriptions in Metzeltin & Lange-Bertalot (1995, 2014) and Mrozińska et al. (2006).

Taxon	Length (µm)	Width (µm)	Length: Width	Striae (in 10 µm)	Stigmata number	Areolae (in 10 µm), morphology	Pole shape	Locality	References
D. clavaherculis (Ehrenberg) Metzeltin & Lange-Bertalot	130–135	33–38	3.9–3.5	8–9	3	10–12 Deep inclined walls surrounded by spine-like projections, dendritic slits below spines	Narrower foot-pole, capitate head-pole though less than D. geminata, distinct constriction of apices and central part	Northern Ireland, Mourne Mountains	Metzeltin & Lange- Bertalot (1995, 2014)
D. curvata (Skvortsov & K.I. Meyer) Metzeltin & Lange-Bertalot	53–120	28–35	1.9–3.4	8–10	1 rarely 2	11–14 Deep inclined walls and dendritic slits with no spine-like projections	Head-pole broadly rounded, foot-pole narrower though rounded	Russia – Siberia, Lake Baikal	Metzeltin & Lange- Bertalot (1995, 2014)
D. dentata (Dorogostaïsky) Skvortzow & K.I. Meyer	76–178	35–54	2.1–3.2	7–9	0	10–11 Deep inclined walls and no dendritic slits with large semicircular apertures, vimines lacking	Capitate though smaller bulbous poles, with inflated central part, distinct constriction of apices and central part	Russia – Siberia, Lake Baikal	Skvortzow & Meyer (1928)
D. geminata (Lyngbye) M. Schmidt	48–132	25–45	1.9–2.9	8–10	1–7	9–12 Deep inclined walls surrounded by spine-like projections, dendritic slits below spines	Distinct capitate head-pole, foot-pole rounded to slightly subcapitate, distinct constriction of apices and central part	Europe, Asia, and North America	Metzeltin & Lange- Bertalot (1995, 2014) Spaulding (2010)
	65–161	36–41	1.8–3.9	7–9	2–5
D. grunowii Lange-Bertalot & Metzeltin	55–85	27–35	2–2.4	10–13	1	15–17 Deep inclined walls and elongated dendritic slits with no spine-like projections	Head-pole blunt and rounded, constriction between central inflation and head-pole poorly defined, foot-pole not bulbous	Russia – Siberia, reservoir in Irkutsk	Metzeltin & Lange-Bertalot (2014)
D. hullii Khan- Bureau sp. nov.	40–60	26.5–30.5	1.5–1.9	9–11	1–4	8-10 Deep inclined walls surrounded by spine-like projections, dendritic slits below spines	Head-pole round, blunt, constriction between central inflation and head pole poorly defined, foot-pole bulb shaped	U.S.A., CT, West Branch, Farmington River	This study
D. laticollis Metzeltin & Lange-Bertalot	57–123	32–42	1.7–2.9	7–9	2–5	8–12 Deep inclined walls surrounded by spine-like projections, dendritic slits below spines	Head-pole round, blunt, constriction between central inflation and head pole poorly developed, foot-pole narrower	North European Russia, Lake Onega	Metzeltin & Lange- Bertalot (2014)
D. pumila Metzeltin & Lange-Bertalot	40–56	25–30	1.6–1.9	8–10	1–2	14 Deep inclined walls, no spine-like projections, dendroid slits nearly flush to mantle	Head-end weakly protracted from the central part, foot-poles broadly rounded	Russia – Siberia, reservoir in Irkutsk	Metzeltin & Lange- Bertalot (1995, 2014)
D. siberica (Grunow) M. Schmidt	70–85	34–40	2–2.1	10–12	1	11–12 Deep inclined walls, no spine-like projections, dendritic slits	Poles very bluntly rounded, foot-pole narrower, constriction between head-pole and central inflation poorly defined	Russia – Siberia, Jenissey River	Dawson (1973),Stoermer et al. (1986), Metzeltin & Lange- Bertalot (2014)
	75–173	33–50	2.2–3.4	10–13	1
D. tatrensis Mrozińska, Czerwik- Marcinkowska & Gradziński	60–99	28–41	2–2.4	13–14.5	1	10–13 Depressed inclined walls and dendroid apertures with no spine-like projections	Head-pole bluntly rounded, constriction between head-pole and central inflation poorly defined	Poland, Slovakia	Mrozińska et al. (2006)

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