Planothidium lagerheimii (Cleve) C.E.Wetzel & Ector

Wetzel, Carlos E. & Ector, Luc, 2014, Planothidium lagerheimii comb. nov. (Bacillariophyta, Achnanthales) a forgotten diatom from South America, Phytotaxa 188 (5), pp. 261-267 : 263

Planothidium lagerheimii (Cleve) C.E.Wetzel & Ector , comb. nov. ( Figs 1–20 )

Basionym: — Cocconeis lagerheimii Cleve, P.T., 1894 . Le Diatomiste 2(19), p. 143, plate 3, figs 21–22.

Synonyms: —= Cocconeis rudis Frenguelli 1953 , Revista del Museo de la Ciudad Eva Peron, Sec. Bot., Tomo VIII, p. 70–71, pl. 1, figs 11–12; = Achnanthes salvadoriana Hust. 1953 , Comun. Inst. Trop. Invest. Ci. Univ. El Salvador, n° 5–6, p. 132, fig. 1; = Achnantheiopsis salvadoriana (Hust.) Lange-Bert. 1997 , Arch. Protistenk., vol. 148, p. 208; = Planothidium salvadorianum (Hust.) Lange-Bert. 1999 , Iconograph. Diatomol., vol. 6, p. 285.

Type locality:— ECUADOR. San-Nicolas, Los Ríos. Freshwater ( Cleve 1894a) .

Material here analysed:— BRAZIL: Rio Grande do Sul, Santa Cruz do Sul, Preto Stream, Rio Pardo hydrographical basin (29°42’36.8”S, 52°24’27.3”W), 01/06/2004. Leg. C.E. Wetzel .

Observations:— Light microscopy ( Figs 7–11 ): Valves are wide lanceolate, with cuneate apices. Valve dimensions (n=25): length 28.0–35.5 µm, width 15.5–20.0 µm. Rapheless valve ( Figs 7, 8, 10, 11 ): Axial area wide, with irregular depressions in a linear apical direction. Central area with a wide elliptic unilateral area (cavum) reaching valve margin. The aperture of the cavum is smaller towards the valve border. Broad and short radiate striae, between 6 and 8 striae (usually 7) in 10 µm, measured at central part of the valve, opposite to the cavum. Raphe valve ( Fig. 9 ): Axial hyaline area in H-format. Fascia absent, sometimes with a striae missing in one side. Raphe branches straight with expanded, drop-like proximal raphe endings and distal ends with a distinct helictoglossae. Delicate striae with high density (between 16–21 in 10 µm, usually 19) and slightly radiate throughout entire valve.

— Scanning electron microscopy ( Figs 12–20 ): Rapheless valve: externally, multiporoid striae composed by two main rows of small irregular rounded areolae (a third smaller in the middle), not interrupted at juncture of valve and valve mantle ( Figs 12, 17 ). Valve mantle shallow, with irregular number of notches, and irregular clusters of areolae ( Fig. 12 ). The valve mantle can present a step interruption of the striae ( Fig. 17 ). Axial and central area presenting irregular deep depressions on valve surface ( Fig. 12 ). Valve interior with large cavum (“hood”) ( Figs 13, 20 ). Striae sunken between strongly silicified raised virgae ( Figs 13, 18 ). Raphe valve: External proximal raphe endings expanded ( Fig. 14 ). Distal raphe endings straight terminating on valve face by a very short T-fissure close to the border ( Figs 14 ). Striae of raphe valve consisting of uniseriate rows composed by rounded pores through the whole valve ( Fig. 14 ). Internally the areolae are occluded and circular close to the axial and central area ( Figs 15, 16 ) while more elongated close to the valve edge ( Fig. 19 ). Proximal ends of raphe not widened, thin and opposite to each other on inner valve surface ( Fig. 15 ). Helictoglossae strongly developed ( Figs 15, 16 ).

Figures

FIGURES 1–11. Planothidium lagerheimii comb. nov. Figs 1–6: Reproduction of original drawings. Figs 1–2. Cocconeis lagerheimii Cleve (1894b, pl. 3, figs 21–22). Figs 3–4. Cocconeis rudis Frenguelli (1953, pl. 1, figs 11–12). Figs 5–6. Achnanthes salvadoriana Hustedt (1953, fig. 1). Figs 7–11. LM images of Planothidium lagerheimii population from southern Brazil (Rio Grande do Sul, Santa Cruz do Sul, Preto Stream, Rio Pardo hydrographical basin).

FIGURES 12–20. SEM images of Planothidium lagerheimii comb. nov. Fig. 12. External view of rapheless valve. Fig. 13. Internal view of raphe valve. Fig. 14. External view of raphe valve. Fig. 15. Internal view of rapheless valve. Fig. 16. Detail of well-developed helictoglossa. Fig. 17. Detail of rapheless valve showing conspicuous grooves and multiseriate striae. Fig. 18. Internal detail of thick silicified virgae of rapheless valve. Fig. 19. Internal detail of uniseriate striae of raphe valve. Fig. 20. Internal detail of rapheless valve showing a well-developed cavum.