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Figure 1. Cleaned cell of Cerataulus smithii in girdle view. Image captured using a light microscope.

Figure 2. Cleaned cell of Cerataulus smithii in valve view. Image captured using a light microscope.

Figure 3. Cerataulus smithii seen in valve view. Image captured using a scanning electron microscope (SEM). Total diameter of the cell is 30 µm.

Figure 4. Cerataulus smithii seen in valve view. Image captured using SEM. Total diameter of the cell is 70 µm.

Figure 5. Detailed view of ocellus of Cerataulus smithii. Image captured using SEM.

Figure 6. Oblique girdle view of Cerataulus smithii. Image captured using SEM. Total diameter of the cell is 32 µm.

Species Name: Cerataulus smithii Ralfs in Pritchard, 1861
Common Name: Diatom
Synonymy: Cerataulus smithi

    Kingdom Phylum/Division Class: Order: Family: Genus:
    Protista Bacillariophyta Mediophyceae     Cerataulus

    Use your mouse to rollover the terms in purple for their definitions. If this feature is not supported by your browser, please refer to the accompanying glossary for terminology.

    Species Description

    When living, cells of this diatom are normally observed in girdle (side) view, appearing drum-shaped (Figure 1). However, cleaned and slide-mounted cells are often viewed from the circular, valve-view perspective (Figure 2).

    Both valves of the siliceous (silica-comprised) shell, called a frustule, bear two prominent projections and two less conspicuous spines (Figure 1). By using a scanning electron microscope (SEM) to view the diatom, the larger projections are revealed to be ocelli, each containing an area of very fine pores surrounded by a rim of silica on the top surface of the projection (Figure 5). The two ocelli are approximately 180 degrees apart near the valve margin. Also oriented 180 degrees apart and 90 degrees from the ocelli are the two smaller spines (Figures 3 & 4). Hollow and cylindrical, these spines form the external part of the rimoportulae.

    Numerous 10-µm areolae are arranged across each valve, with approximately six on the valve surface and 7-8 near the margin. In addition to these pores, the valve is granulated in a random pattern near the center. Each valve of the diatom is bordered by several bands, which together are known as the cingulum. Individual bands bear a double or triple row of 12-16 10-µm pores (Figure 6). When both valves are fitted together as a completed frustule, these bordering bands form a portion of the connective zone called the girdle.

    Living cells are filled with chloroplasts and are often coated with small organic particles called detritus, obscuring the structures used to identify the species.

    Potentially Misidentified Species

    The systematics, or classification, of C. smithii is confused, with the species often appearing in the scientific literature as Cerataulus radiatus. Some speculation also exists that the organism may be misplaced in the genus Cerataulus (Round et al. 1990) because the key characteristics of members of this genus differ from those of C. smithii in two major ways:

    (1) the ocelli do not point in opposite directions; and
    (2) the foramina - perforations on the surface of the valve that are connected through the valve to the larger holes on the opposing surface, called loculate areolae - are located on the exterior of the valve rather than the interior.



    Considered a benthic species (bottom-dwelling or surface-attached), C. smithii occurs only occasionally as plankton suspended in the water column. The diatom secretes mucilage through the ocelli, which it uses as an adhesive to attach to sand grains.

    Regional Occurrence & IRL Distribution

    C. smithii has a worldwide distribution in temperate and tropical shallow waters, including the Indian River Lagoon. 



    In valve view, the circular surfaces of each valve range from 28 µm to 120 µm in diameter.


    Although C. smithii is found throughout the IRL at most times of the year, it is never considered abundant.


    C. wailesii is subject to parasitic infections by the nanoflagellate Pirsonia diadema, which is at least partly specific to this diatom (Kuehn 1998). Fatal infections by the bacterium Alteromonas sp. are also known (Nagai & Imai 1998). It is likely other pathogens exist.


    No information is available at this time


    No information is available at this time


    No information is available at this time


    Hargraves, PE. 2002. Diatoms of the Indian River Lagoon, Florida: an annotated account. Fla. Sci. 65: 225-244.

    Round, FE, Crawford, RM & DG Mann. 1990. The Diatoms: Biology & Morphology of the Genera. Cambridge University Press, Cambridge. 747 pp.

    Tomas, CR. 1997. Identifying Marine Phytoplankton. Academic Press, San Diego.

Unless otherwise noted, all images and text by PE Hargraves
Editing and page maintenance by LH Sweat
For questions, comments or contributions, please contact us at:
Page last updated: 10 October 2011


Regularly repeated perforations through the cell wall.


Tube-like openings through the cell wall, each with an internal flattened tube or lip-like slit; also called labiate processes.


Groups of small pores surrounded by thickened hyaline rims and raised from the surface of the valve.

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