Diatoms: Biology and Morphology of the Genera by F. E. Round & R. M. Crawford & D. G. Mann

Author:F. E. Round & R. M. Crawford & D. G. Mann [Round, F. E.]
Language: eng
Format: azw3
Publisher: Cambridge University Press
Published: 1990-05-25T04:00:00+00:00

Toxarium J. W. Bailey 1854. Smithsonian Contrib. Knowl. 7 (3): 15

T: T. undalatum Bailey

Cells needle-likea–c in valve and girdle view, sometimes curved or undulate. Plastids unrecorded. Growing attached or perhaps only intermingled with other epiphytes on marine algae and angiosperms. Common, especially in tropical/subtropical waters.

Valves up to 1 mm long, slightly expanded at both apices and at the centre;b slightly curved or with undulate margins.j Valve face flat; mantles distinct but shallow. No distinct sternum.a, d, f Areolae scattered over much of the valve face but in fairly well-defined rows along the edge of the valve face and on the mantle; simple and round internally and externally. Vela are present deep within the areolae, but we have no detail of their structure. There is no rimoportula nor any apical pore plate but a slight development of a flange (septum?) at the apices of T. hennedyanum. Copulae of T. hennedyanum of two distinct types: valvocopula narrow with a single row of pores next to the valve edge; second band broader and thinner with similar row of pores next to the valvocopula and then a broad area bearing rows of pores which run towards the opposite edge of the band. Occasionally pores are joined to form ‘tears’ in the band.

This genus was placed in Synedra soon after its initial description and Hustedt (1927–66) was not prepared to recognise it as a separate genus. In fact it probably has little relationship to Synedra: Hustedt was not aware, of course, of the absence of rimoportulae (Round, 1979a) although he noted the absence of a sternum. This latter is a rather rare condition in pennate genera and coupled with it is a distinctive semi-circular arrangement of the areolae at the apices. The only species other than the type is the non-undulate T. hennedyanum but taxa in VanLandingham (1978) need checking. ‘Synedra reinboldii’ was also placed in Toxarium by Mills (1933–5) but this has a very distinct rimoportula and cribra (see p. 428) – it has been placed in a new genus Trichotoxon (Reid & Round, 1987).

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