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Figure 1.

Figure 2.

Figure 3.

Figure 4.

Species Name: Cerataulina bicornis (Ehrenberg) Hasle
Common Name: None
Synonymy: None

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

    Species Description

    The cells are chain-forming (Fig. 1) with individual cells forming elongated cylinders, the length (pervalvar axis) mostly 3-10 times the diameter (apical axis). Valves are round and have two wing-like projections on opposite margins with pointed tips (Fig. 2, arrow) that fit into furrows on adjacent valves, and ribbed ocelli near the bases of the projections (Hasle & Syvertsen 1980). Location of the projections varies among adjacent cells so that one valve may appear in broad girdle view and the other in “narrow” girdle view, so that the chain appears twisted (Fig. 1). There is a rimoportula near the margin that is only visible in valve view. Girdle bands are numerous. There are many small chloroplasts distributed around the cell periphery (Fig. 2, LM phase contrast, from a crude culture). The resting spore is quite distinctive (Fig. 3, LM phase contrast). It is heavily siliceous, with two elevations with spines on the primary valve reminiscent of the vegetative cell, between which is a shorter tube that is probably the external part of a rimoportula (Fig. 4, SEM). The secondary valve is elongate, ending in a single pointed process.  This spore was originally described as a distinct genus and species from fossil deposits (Syringodium bicorne, Hasle & Sims 1985).

    Literature records report a range of 5-75µm in diameter, and up to 200µm in pervalvar axis. It has a global distribution in subtropical and tropical coastal waters, but its similar appearance to C. pelagica suggests the likelihood of misidentification. For example, Saunders (1968) described the resting spore as C. pelagica and gave detailed distribution in Florida waters. They are difficult to differentiate, but C. pelagica has a central rimoportula, inconspicuous girdle bands, smaller marginal wing-like elevations, lacks resting spores, and is more common in temperate and boreal waters. Hustedt (1930) also illustrated the spore, but attributed it to C. bergonii, which is a synonym of C. pelagica. Both C. pelagica and C. bicornis are found in the IRL, sometimes in great abundance.


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    Hasle GR, Sims PA. 1985. The morphology of the diatom resting spores Syringidium bicorne and Syringidium simplex. Brit Phycol J 20:219-225.

    Hasle GR, Syvertsen EE. 1980. The diatom genus Cerataulina: Morphology and taxonomy. Bacillaria3:79-113.

    Saunders RP. 1968. Cerataulina pelagica. Florida Board Conserv Mar Res Lab. Leaflet Series Vol 1, Pt 2 (Diatoms) No. 5:1-11.

Unless otherwise noted, all images and text by PE Hargraves
Editing and page maintenance by LH Sweat
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Page last updated: 28 April 2015

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