Tetracyclus
Ralfs 1843 Category: Araphid
TYPE SPECIES: Tetracyclus lacustris Ralfs
Smallest to largest - 3 taxa sorted by maximum length
Image Credit: Gene Stoermer, Ian Bishop
CLASS: Fragilariophyceae
ORDER: Tabellariales
FAMILY: Tabellareaceae
- Striae pattern scattered or less regular at sternum
- Valve mantle with prominent hyaline step
- Copulae with multiple ornamented pattern
Frustules of Tetracyclus are heavily silicified. Valves are isopolar, with a flat surface. The valve mantle is relatively deep and possesses a prominent hyaline step. The valve face may be elliptical to elongate (some taxa are even circular) and the apicies are often capitate. Primary internal transapical ribs are present, and some species may possess secondary and tertiary transapical ribs. The valve margin may be expanded centrally. Striae are uniseriate. The striae are parallel to slightly radiate, and extend over the mantle. At the sternum, the stria pattern is scattered, or less regular than other parts of the valve. That is, the axial area has indefinite margins. Apical pore fields are present. The cingulum is composed of several open bands. Valves may have up to two rimoportulae (in some cases more than two rimoportulae). The rimoportulae are positioned near the valve center or in the mantle area, making them difficult to see using LM. Cells form zig-zag colonies joined by mucilage pads. Alternatively, there are species which have valve face to face colonies joined by what appear to be very small spines.
According to Williams (1987), the only extant species that possess rimoportulae are T. emarginatus and T. rupestris.
Tetracyclus is considered a close relative of Tabellaria. Extinct species of Tetracyclus occur in the fossil lacustrine deposits of western North America. In cold water habitats of the Northern Hemisphere, the species T. glans, T. emarginatus and T. rupestris occur in high latitude and high altitude oliotrophic lakes and in moss habitats.
Cite This Page:
Spaulding, S., and Edlund, M. (2008). Tetracyclus. In Diatoms of the United States. Retrieved September 30, 2016, from http://westerndiatoms.colorado.edu/taxa/genus/Tetracyclus
Contributor: Sarah Spaulding | Mark Edlund - December 2008
Citations
Williams, D.M. (1985). Morphology, taxonomy and inter-relationships of the ribbed araphid diatoms from the genera Diatoma and Meridion (Diatomaceae: Bacillariophyta). Bibliotheca Diatomologica 8: 1-228.
Williams, D.M. (1987). Observations on the genus Tetracyclus Ralfs (Bacillariophyta) I. Valve and girdle structure of the extant species. British Phycological Journal 22: 383-399. 10.1080/00071618700650451
Williams, D.M. (1989). Observations on the genus Tetracyclus Ralfs (Bacillariophyta) II. Morphology and taxonomy of some fossil species previously classified in Stylobium Ehrenberg. British Phycological Journal 24: 317-327.
Williams, D.M. (1990). Cladistic analysis of some freshwater araphid diatoms (Bacillariophyta) with particular reference to Diatoma and Meridion. Plant Systematics and Evolution 171: 1615-6110.
Williams, D.M. (1990). Distrionella D.M. Williams, nov. gen., a new araphid diatom (Bacillariophyta) genus closely related to Diatoma Bory. Archiv für Protistenkunde 138: 171-177.
Williams, D.M. (1990). Examination of auxospore valves in Tetracyclus from fossil specimens and the establishment of their identity. Diatom Research 5: 198-194.
Williams, D.M. (1996). Fossil species of the diatom genus Tetracyclus (Bacillariophyta, ‘Ellipticus’ species group): Morphology, interrelationships and the relevance of ontogeny. Philosophical Transactions of the Royal Society of London, B, 351:1 759-1782. 10.1098/rstb.1996.0156
Williams, D.M. and Li, J. (1990). Observations on the diatom genus Tetracyclus Ralfs (Bacillariophyta) III. Description of two new species from Chinese fossil deposits. British Phycological Journal 25: 335-338.
Links
Index Nominum Algarum (INA)
California Academy of Sciences (CAS)
August 19th, 2013 - Correction to genus description
The guide points and text describing the features of the genus was corrected to conform more to the work of Williams (1987). - S. Spaulding