Brachysira neoacuta

Lange-Bert. in Lange-Bert. and Gerd Moser 1994      Category: Symmetrical biraphid

REPORTED AS: Anomoeoneis serians var. acuta (Patrick & Reimer 1966, pg. 378, pl. 33, fig. 2) 

Brachysira microcephala


Brachysira ocalanensis

LM scalebar = 10 µm = 80 pixels.


Contributor: Paul Hamilton - December 2010
Length Range: 31-51 µm
Width Range: 6.5-9 µm
Striae in 10 µm: 24-26


Valves are rhombic-lanceolate with straight margins and acute, narrow, rounded apices. Striae are radiate throughout; striae along the center contain two to five areolae and striae at the apices with a single areola. The axial area is straight. The central area is asymmetrically rounded, barely wider than the axial area. The raphe is positioned within two ribs on the external valve face. The ribs terminate within the central area and at the apices. The raphe is straight, curving weakly at the proximal and distal ends.The proximal raphe ends are straight and the distal fissures have T-shaped endings. Areolae are elongated box-like slits with rounded ends, oriented to the transapical axis. Spaces between the areolae give the appearance of longitudinal undulations. A thickened rib is present along the valve margin (except at the apices) separating the valve face from the mantle. The mantle possesses a single row of elongated pores. One or two Voigt discontinuities are present on the secondary side of each valve. Valve face papillae, if present, are small.

In SEM, the internal proximal raphes terminate at small helictoglossae. Areolae are covered internally by hymenes.

Original Description

Author: Lange-Bert. in Lange-Bert. and Gerd Moser 1994
Length Range: 40-65 µm
Width Range: 6-9 µm
Striae in 10 µm: 24-26

Original Description

Valvae lanceolatae apicibus acute rotundatis marginibus ad apices modice concavis (non rectis nec convexis), 40-65 μm longae, 6-9 μm latae. Raphe modice arcuata fissuris internis/externis minime lateralibus. Area axialis modice angusta, area centralis satis parva (numquam ampla) plusminusve rhombica ad instar. Striae transapicales magnopere radiantes usque ad apices, 24-26 in 10 μm. Inordinatio Voigtii distincta. Structurae submicroscopicae: Papillae in fronte adsunt. Alia signa typica submicroscopica vide in Fig. 18:3,4.

Schalen im Umriβ ähnlicher B. wygaschii als B. serians s. str., aber schmaler lanzettlich mit länger vorgezogenen, noch spitzer gerundeten Enden. Die Schalenränder vor den Enden sind schwach konkav und nicht konvex. Länge 40-65 μm, Breite 6-9 μm. Raphe, Axial- und Zentralarea ähnlich B. wygaschii, Zentralarea tendenziell etwas kleiner. Streifen durchweg stark radial, 24-26/10 μm, Voigt-Diskordanz deutlich. REM: Weitgehend Übereinstimmung mit B. wygaschii, aber mit kleinen Wärzchen auf der Schalenoberfläche.

Original Images

Cite This Page:
Hamilton, P. (2010). Brachysira neoacuta. In Diatoms of the United States. Retrieved April 22, 2018, from

Species: Brachysira neoacuta

Contributor: Paul Hamilton

Reviewer: Sarah Spaulding


Lange-Bertalot, H. and Moser, G. (1994). Brachysira Monographie der Gattung. Bibliotheca Diatomologica 29: 1-212.

Shayler, H.A. and Siver, P.A. (2004). Description of a new species of the diatom genus Brachysira (Bacillariophyta), Brachysira gravida sp. nov. from the Ocala National Forest, Florida, U.S.A. Nova Hedwigia 78: 399-409.

Siver, P.A. and Hamilton, P.B. (2011). Diatoms of North America: The Freshwater Flora of Waterbodies on the Atlantic Coastal Plain. Iconographia Diatomologica 22.

Links & ID's

Index Nominum Algarum (INA)

California Academy of Sciences (CAS)

Brachysira neoacuta CAS

North American Diatom Ecological Database (NADED)


Autecology Discussion