Eupodiscus radiatus

J.W.Bailey 1851      Category: Centric
SYNONYM(S): Aulacodiscus radiatus (J.W.Bailey) Brightw. | Roperia radiata (J.W.Bailey) Kuntze 

Eunotia zasuminensis


Fallacia latelongitudinalis

LM scalebar = 10 µm = 20 pixels.


Contributor: Emily Nodine - June 2011
Diameter: 60-208, usually 80-120 µm
Mantle Height: 10-17 µm
Rows of areolae in 10 µm: 3-4


Valves are circular with hexagonal areolae uniformly distributed on the valve face, 3-4 in 10 µm. The valve surface is flat or slightly concave and the central valve is not distinguished. Four (although sometimes 3-6) prominent ocelli are evenly spaced on the margin of the valve face, along a narrow ridge formed by a slightly scalloped edge. The valve face/mantle transition otherwise appears smoothly rounded. Areolae continue beyond the transition onto the mantle, where they are slightly smaller, usually 5-6 in 10 µm. Areolae are arranged in a radiate pattern from center of the valve, although they are sometimes irregularly organized. Diameter of the ocelli ranges from 3.5-10 µm and is roughly proportional to valve diameter. Rimoportulae are present at the valve/mantle transition and are interspersed between the ocelli, with one or two rimoportulae between each pair of adjacent ocelli. External openings of rimoportulae are flush with the valve face and therefore difficult to detect; on the inside of the valve rimoportulae are visible under SEM at the valve-mantle junction. The rimoportulae are small and in many specimens these are not preserved. Mantle margins are variously ornamented and often form a slight circumferential ridge.

Original Description

Author: J.W.Bailey 1851
Diameter: µm
Rows of areolae in 10 µm:

Original Description

In form, size, and reticulation resembling the Coscinodiscus radiatus of Ehrenberg but having four (or more?) foot-like projections near the margin. A common form in the Southern States.

Original Images

Cite This Page:
Nodine, E. (2011). Eupodiscus radiatus. In Diatoms of the United States. Retrieved April 21, 2018, from

Species: Eupodiscus radiatus

Contributor: Emily Nodine

Reviewer: Sarah Spaulding


Bailey, J.W. (1851). Microscopical observations made in South Carolina, Georgia, and Florida . Smithsonian Contributions to Knowledge 2(8): 1-48.

Fernandes, L.F. (2003). New observations on frustule morphology of Eupodiscus radiatus Bailey and Fryxelliella floridana Prasad. Brazilian Journal of Biology 63(3): 411-421.

Foged, N. (1986). Diatoms in Gambia. Bibliotheca Diatomologica 12. J. Cramer, Berlin.

Hendey, N.I. (1964). An Introductory Account of the Smaller Algae of British Coastal Waters. Her Majesty’s Stationery Office, London.

Navarro, J.N. (1981). A survey of the marine diatoms of Puerto Rico II. Suborder Biddulphiineae: Families Biddulphiaceae, Lithodesmiaceae and Eupodiscaceae. Botanica Marina 24: 615-630.

Prasad, A.K.S.K. and Nienow, J.A. (1988). Rimoportulae in Eupodiscus radiatus (Bacillariophyceae) from the Northeastern Gulf of Mexico. Journal of Phycology 24: 120-123.

Round, F.E., Crawford, R.M. and Mann, D.G. (1990). The Diatoms. Biology and Morphology of the Genera. Cambridge University Press, Cambridge, 747 pp.

Sullivan, M.J. (1986). A light and scanning electron microscope study of Eupodiscus radiatus Bailey (Eupodiscaceae). In Ricard, M. (Ed.) Proceedings of the Eighth International Diatom Symposium, Paris, 1984, Otto Koeltz, Koenigstein, pp. 113-123.

Sullivan, M.J. and Porguen, V. (1990). A new species of Eupodiscus closely related to the generitype E. radiatus (Eupodiscaceae). . In Simola, H. (Ed.) Proceedings of the Tenth International Diatom Symposium, 1988, O. Koeltz, Koenigstein, pp. 117-126.

Van Heurck, H. (1881). Synopsis des Diatomées de Belgique. Atlas. Ducaju & Cie., Anvers. pls 31-77.

Links & ID's

Index Nominum Algarum (INA)

Original INA

California Academy of Sciences (CAS)

Eupodiscus radiatus CAS

North American Diatom Ecological Database (NADED)


Autecology Discussion

Eupodiscus radiatus was collected in a water sample from Charlotte Harbor, on Florida’s west coast in Charlotte County, Florida. It is also common in sediment cores from Charlotte Harbor and Florida Bay, Monroe County, Florida. It occurs in marine to brackish habitats, but it remains unclear whether the species is epiphytic, planktonic, or benthic as there are few records of living cells. It has previously been identified as a co-dominant species in phytoplankton of the northeastern Gulf of Mexico off Florida’s north coast (Prasad and Nienow 1988) and described as common off the American coast, particularly in southern states (Bailey 1851, Hendey 1964). Prasad and Nienow (1988) found it frequently in plankton samples collected in November, January, and February, but it was absent in April collections. The Charlotte Harbor water sample was collected in June 2010, when salinity was approximately 19.6 ppt. Eupodiscus radiatus was absent from sediment samples taken concurrently.

Other distributional records include the Indian Ocean (van Heurck 1896), the southwestern coast of the British Isles (Hendey 1964), coastal Gambia (Foged 1986), estuaries of Southern Brazil (Fernandes 2003), and elsewhere in the Caribbean (e.g., Navarro 1981).


Eupodiscus radiatus from Florida Bay sediment core

Credit/Source: Image by Anna Wachnicka