Corethron

From Frustule

GENUS Corethron
Castracane (1886)
Taxonomic Information Generitype: Not designated. [Corethron criophilum Castracane, 1886, by construction.] Genus Description: The new forms upon which this genus is established are exclusively Antarctic. They have a more or less cylindrical form, and are terminated by hemispherical surfaces, the base being surrounded by a corona of awns, which are more or less thick and long, and are smooth or thorny. Although from the rarity of these interesting organisms it was not possible to determine their siliceous or non-siliceous character by means of acids, this determination was made by the application of strong heat for a protracted period. This produced no visible change on their form, so that their diatomaceous nature could not be doubted.

List of Species belonging to the Genus Corethron

General Remarks

Remarks:

The name that has been proposed for the genus has reference to the `broom'-like appearance of the frustules, and the following generic definition may be given: Frustula cylindrica, libera (?); valvis convexis, setarum radiantium corona cinctis. According to the character of the connecting zone and awns this genus may be divided into two sections, embracing A. Forms with simple smooth connecting zones and smooth awns. B. Forms with complex annulate connecting zones and echinated awns.

Differentiation:

Although the presence of long awns radiating round the valves might affiliate the present organisms to the genus Bacteriastrum, the two groups of forms differ very notably in other respects. Thus in the former there is as yet no proof that the frustules are arranged in series, while their general form is cylindrical or cylindroidal - one axis being much longer than the other - and the awns are never tortuous or dichotomous. But these characteristics are not wanting in the genus Bacteriastrum, hence the new series of forms, which unquestionably have certain affinities to Chaetoceros, must be regarded as forming a transition to the tubulate Rhizosoleniae.

Useful References

• Castracane, F., 1886. The voyage of the H.M.S. Challenger, Report on the Diatomaceae. In Murray, J. (ed.), Report on the Scientific Results of the Voyage of H.M.S. Challenger during the years 1873-1876, Botany. Her Majesty's Stationery Office, London, 2:1-178.