Frustulia capitata

Graeff and Kociolek 2011      Category: Symmetrical biraphid

REPORTED AS: Frustulia weinholdii (Patrick and Reimer 1966) 

Frustulia bahlsii


Frustulia crassinervia

LM scalebar = 10 µm = 80 pixels.


Contributor: Carrie Graeff - October 2011
Length Range: 26-43 µm
Width Range: 7.0-8.5 µm
Striae in 10 µm: 34-36 at the center, 35-38 at the ends


The valves are linear-lanceolate with capitate to subcapitate apices. The striae are parallel or slightly radiate at the valve center, parallel along the length of the valve, and convergent at the ends of the valve. Areolae comprising the striae are round or oval. At the central area, the striae give the central area a relatively linear appearance, though one or a few areolae can extend onto the central area. Internally, the longitudinal ribs terminate well before both the helictoglossae. The longitudinal ribs are complete only on the side of the valve to which the proximal raphe ends are deflected.

F. capitata is a species that has been separated from the broad taxon concept of F. weinholdii established by Patrick and Reimer (1966) where they described the apices of F. weinholdii as round to capitate. At least two additional species have since been separated from F. weinholdii, including those populations with relatively round or slightly rostrate apices. Under the broad concept of the taxon, reports of F. weinholdii have been numerous in the United States.

Original Description

Author: Graeff and Kociolek 2011
Length Range: 26.0-43.0 µm
Width Range: 7.0-8.5 µm
Striae in 10 µm: 34-36 at the center, 35-38 at the ends

Original Description

Valves are linear or linear-lanceolate with subcapitate or sometimes slightly capitate apices. In some specimens, the protracted portion of the valve apices is bent. Striae are slightly radiate, or less commonly parallel at the valve center, parallel towards the poles, and convergent at the poles. Most areolae comprising the striae are round or oval, but elongated areolae are common, especially at the apices. The majority of the areolae at the apices are relatively small and round compared to areolae on the rest of the valve. The central area is relatively linear. Internally, areolae are occluded. The dorsal longitudinal rib is interrupted in the center and tapers before reaching the central nodule, but the ventral longitudinal rib is either continuous or interrupted by an areola. External distal raphe ends terminate in a shallow transverse depression, and the external proximal raphe ends curve unilaterally. The cingulum is comprised of an ornamented closed valvocopula and a few open girdle bands, each with at least one row of poroids. One distal end of the girdle band can be significantly wider than the majority of the girdle band.

Original Images

Cite This Page:
Graeff, C. (2011). Frustulia capitata. In Diatoms of the United States. Retrieved April 26, 2018, from

Species: Frustulia capitata

Contributor: Carrie Graeff

Reviewer: Sarah Spaulding


Graeff, C.L. and Kociolek, J.P. (2011). Investigations of the Frustulia weinholdii species complex with descriptions of three new species, F. capitata, F. latita, and F. soror from South Carolina and Hawaii. Proceedings of the Academy of Natural Sciences of Philadelphia 161: 43-59.

Wallace, J. (1960). New and variable diatoms. Notulae Naturae 331: 1-8.

Links & ID's

Index Nominum Algarum (INA)

California Academy of Sciences (CAS)

North American Diatom Ecological Database (NADED)


Autecology Discussion