Bicudoa amazonica C.E. Wetzel, Lange-Bertalot & Ector, 2012

Wetzel, Carlos E., Lange-Bertalot, Horst, Morales, Eduardo A., Bicudo, Denise De C., Hoffmann, Lucien & Ector, Luc, 2012, Bicudoa amazonica gen. nov. et sp. nov. (Bacillariophyta) - a new freshwater diatom from the Amazon basin with a complete raphe loss in the Eunotioid lineage, Phytotaxa 75 (1), pp. 1-18 : 7-9

Bicudoa amazonica C.E. Wetzel, Lange-Bertalot & Ector sp. nov.

Diagnosis microscopio photonico: Frustula aspectu cinguli fere rectangulata. Valvae late ellipticae, lineari-ellipticae ad lineares apicibus cuneatis denique curte rostratis. Valvae dorsiventrales quia ad axem apicalem leviter ad levissime asymmetricae margine una semper convexa altera modice concava in mediis partibus quoad specimina media et maiora. Longitudo 40–120 μ m, latitudo 17–20 μ m. Area axialis (id est sternum) angustissima plerumque excentrica sita. Areae angustae marginales prope limbos adsunt. Alterae areae absunt. Systema raphidea nulla. Striae transapicales, sicut in Eunotia , subparallelae saepe plusminusve irregulariter sitae inter se, sub apices transientes distincte radiantes, 10–12 in 10 μ m, sub apices modice densius sitae usque ad 16 in 10 μ m. Interstriae comparate latiores. Areolae vix aspectabiles quia circiter 75–80 in 10 μ m. Structura chromatophorum incognita. Diagnosis microscopio electronico: Aspectus externus: Frontes valvarum fere planae cum foraminibus areolarum uniseriatis omnino comparate minimis circularibus (hic apertis) diameter circiter 0.1 μ m. Series foraminum curte interruptae sterno angustissimo et latius interruptae ad iuncturam inter frontem et limbum valvae ubi series apicalis spinarum verrucosa num est tum series continuantes in limbis. Campi porellorum absunt. Aspectus internus: Superficies interna perforata areolis circularibus crateriformibus apertis. Depressiones transapicales id est alveoli vacant. Systema raphidea ut in familia Eunotiaceae sive ut in familia Bacillariaceae nulla. Etiam rimoportulae et porelli apicales ut in familia Fragilariaceae et alteris familiis diatomearum araphidearum vacant. Cingulum frustulorum: cingulum utraeque valvae 3–10 copulis apertis vel clausis constans. Omnes copulae preditae multis areolis uniseriatis transapicaliter (vel quodammodo pervalvariter ita ut in Eunotia nec in familia Fragilariaceae vel alteris familiis araphideis).

Light microscopy observations: —Valves isopolar, moderately dorsiventral, broadly linear with slightly constricted center in large specimens; cuneate to sub-rostrate ends ( Figs 7–13 ). Dorsal margins consistently convex. Ventral margins variable, either less concave in small valves or nearly straight to concave in mediumsized and large specimens. Length 40–120 µm, width 17–20 µm. Axial area or sternum extremely narrow, sometimes displaced toward ventral side of valve ( Fig. 8 ) or centrally positioned ( Fig. 9 ). Narrow lateral area located close to the valve margins, visible in both valves and girdle view. Raphe system, helictoglossae and rimoportulae lacking. Transapical striae subparallel often irregularly spaced, 10–12 in 10 µm, becoming radiate toward the ends where they are more densely spaced (up to 16 in 10 µm) ( Fig. 12 ). Costae comparatively much wider. Areolae observable in LM. Plastids unknown. Frustules rectangular in girdle view ( Fig. 14 ). Cells forming band-like colonies (no more than 4 joined cells observed).

Scanning electron microscope observations: —In external view, valve face slightly curved with a shallow longitudinal depression near the valve center ( Fig. 21 ). Striae uniseriate situated both on valve face and mantle, interrupted by lateral area developing on the junction between valve face and mantle ( Figs 22–25 ). Areolae small, circular with foramina ca. 0.1 µm in diameter ( Fig. 22 ). Each foramen lies in a shallow depression visible in oblique view ( Figs 23–25 ). Valve face showing wart-like growths and siliceous thickenings, which allow the connection between contiguous valves ( Fig. 25 ). Sternum narrow, sometimes displaced toward the ventral side of the valve. Apical pore fields absent. The cingulum is composed of 3–10 open copulae that are perforated by pervalvar multiporoid striae arranged in discernible rows ( Fig. 27 ). Girdle band areolae density 75–80 in 10 µm. A small linear depression is present near the apex at the junction between valve face and mantle. In both external and internal view, rimoportulae are always absent. Internally, but never in external view, one raphe slit vestige is present in some specimens ( Figs 28, 30–31 ), but in most cases it is completely lacking ( Figs 28 and 32 ).

Type: — BRAZIL. Amazonas: Rio Negro basin, Alto Rio Negro , 0° 30’ 43’’ S, 64°49’45’’W, 11 March 2005; Wetzel C. E. & Ector L., sample n° 265; Holotype here designated SP –400.480, depicted here in Fig. 8 , deposited at the ‘ Herbário Científico do Estado Maria Eneyda P. Kauffmann Fidalgo’( SP), São Paulo, Brazil. Sample from feces of an adult specimen of the freshwater turtle Podocnemis erythrocephala Spix (1824) . Isotypes: slide BR –4167 (Meise) and slide BM –101392 (London).

Etymology: —The new genus is dedicated to Prof. Dr. Carlos Eduardo de Mattos Bicudo at the ‘Instituto de Botânica de São Paulo’ for his pioneering work on freshwater microalgae in Brazil and for the relevant role on the formation of Brazilian phycologists; ‘ amazonica’ refers to the type locality.

Additional material examined: — BRAZIL. Amazonas : Rio Negro basin, Alto Rio Negro, 03 March 2005; Wetzel C . E . & Ector L ., phytoplankton, sample n° 82; SP–400.297; BRAZIL. Amazonas : Rio Negro basin, Alto Rio Negro, 04 March 2005; Wetzel C . E . & Ector L ., periphytic biofilm growing on submerged Arecaceae palm tree, sample n° 104; SP–400.319; BRAZIL. Amazonas : Rio Negro basin, Alto Rio Negro, 04 March 2005; Wetzel C . E . & Ector L ., phytoplankton, sample n° 106; SP–400.321; BRAZIL. Amazonas : Rio Negro basin, Alto Rio Negro, 04 March 2005; Wetzel C . E . & Ector L ., periphytic biofilm growing on a submerged trunk, sample n° 116; SP–400.331; BRAZIL. Amazonas : Rio Negro basin, Alto Rio Negro, 04 March 2005; Wetzel C . E . & Ector L ., phytoplankton, sample n° 117; SP–400.332; BRAZIL. Amazonas : Rio Negro basin, Alto Rio Negro, 11 March 2005; Wetzel C . E . & Ector L ., phytoplankton, sample n° 260; SP–400.475; BRAZIL. Amazonas : Rio Negro basin, Alto Rio Negro, 11 March 2005; Wetzel C . E . & Ector L ., phytoplankton, sample n° 261; SP–400.476.

Figures

FIGURES 7–20. LM micrographs (bright field optics) of Bicudoa amazonica (Figs 7–14). Holotype population from the Rio Negro hydrographical basin, Brazil (SP–400.477). Fig. 7 Large cell showing slight dorsiventrality and irregular pattern of striae; Fig. 8 Holotype specimen; Figs 7–13 Micrographs illustrating size reduction series in the type population; Fig. 14 Two cells in connective view; Figs 15–17 Three Eunotia species similar in size and shape: Fig. 15 Eunotia pileus var. guianense (Ehrenberg) E. Reichardt; Fig. 16 Eunotia coringii Metzeltin & Lange-Bertalot; Fig. 17 Eunotia ventriosa R.M. Patrick. Note the helictoglossae present and visible on all Eunotia species (black arrow); Figs 18–20 Size reduction series of Fragilariforma hamiltonii Metzeltin & Lange-Bertalot. All specimens from the Rio Negro basin. Scale bar: 10 µm.

FIGURES 21–27. SEM micrographs of Bicudoa amazonica in external view. Fig. 21 Whole frustule in valvar view showing irregular silica deposition along the central part of the valve; central valve face with somewhat concentrated silica deposition at the apical axis; Fig. 22 Valve face apex detail showing the complete absence of raphe aperture system; small foramina forming the striae; Figs 23–24 Detail of both extremities showing reduced slightly radiate striae; note the absence of apical pore fields and external raphe openings on the mantle; axial area narrow, more or less eccentric; Fig. 25 Apex detail with small wart-like silicate on the valve edges (arrow); Fig. 26 Detail of apical valve outline in oblique view; Fig. 27 Detail of one valve and the cingulum in girdle view showing perforated Eunotia-like open copulae (white arrows) with multiporoid striae. Note the numerous open connective bands. Scale bars: Fig. 21: 10 µm; Figs 22–25: 2 µm; Figs 26–27: 5 µm.

FIGURES 28–32. SEM micrographs of Bicudoa amazonica in internal view. Apices details showing the absence of structures typical of Eunotiophycideae (raphe, helictoglossae and rimoportulae). Fig. 28 Valve with vestigial raphe at both extremities (arrows); Fig. 29 Detail of apex with no vestigial raphe; Figs 30–32 Vestigial slit (Figs 30–31) until the complete raphe loss (Fig. 32) in different individuals of the type population. Raphe slits rarely found. Striae interrupted and misaligned near the ventral margin. Scale bars: Figs 28–29: 10 µm; Figs 30–32: 5 µm.