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Diatom Glossary


Species Name: 

Triceratium bicorne

   
Common Name:      None

 

I.  TAXONOMY

KINGDOM DIVISION CLASS GENUS
Protista
Bacillariophyta Mediophyceae Triceratium

     


Figure 1.


Figure 2.

 

SPECIES NAME: 
Triceratium bicorne Cleve

COMMON NAME:
None

SPECIES DESCRIPTION:
There has been considerable confusion about this species, and it is often subsumed into Triceratium dubium Brightwell, which has a very similar construction but is mostly 6-sided.  This confusion is a common situation in the phenotypic taxonomy of the genus, and there is no consensus as to the genus or species limits of many taxa within the family Triceratiaceae. 

The valves of T. bicorne are quadrate (Fig. 1, SEM) with ocelli at two of the corners and external tubes of the rimoportulae at the other two corners (Fig. 1 and Fig. 2, SEM detail of Fig. 1, arrow).  The valve surface is slightly convex and composed of pseudoloculi enclosing clusters of areolae that are more or less radially arranged.  Minute spines are scattered over the pseudoloculus walls (Fig. 2).  These features are shared with T. dubium (Fernandes et al. 2001).  Although it seems rational to include T. bicorne with T. dubium, a recent study has documented distinct genetic differences between the two (Ashworth et al. 2013; MP Ashworth, personal communication, 9 Feb 2015).

Because T. bicorne was only seen once, nothing can be said about its distribution and abundance; it is clearly a rare species.  It would be useful to look at morphological variation within a population to discern phenotypic support (e.g. Cox 2014) for genetic distance between the two similar species.

 

REFERENCES

Ashworth MP, Nakov T, Theriot EC. 2013. Revisiting Ross and Sims (1971): Toward a molecular phylogeny of Biddulphiaceae and Eupodiscaceae (Bacillariophyceae). J Phycol 49:1207-1222.

Cox EJ. 2014. Diatom identification in the face of changing species concepts and evidence of phenotypic plasticity. J Micropal 33:111-120.

Fernandes LF, Sousa-Mosimann RM. 2001. Triceratium moreirae sp. nov. and Triceratium dubium (Triceratiaceae – Bacillariophyta) from estuarine environments of southern Brazil, with comments on the genus Triceratium CgG. Ehrenberg. Rev Brasil Biol 61(1):159-170.

 

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