Taxonomy and nomenclature

The genus Trimastix was first described in 1880 by the English protistologist W. Saville Kent. The description is found on pp. 310-315 in the first volume of his 3-volume treatise, Manual of the Infusoria. The genus name is derived from Latin words meaning "three" and "thread", and refers to Kent's observation of three flagella, one anterior, one lateral, and one posterior, in these cells. Since it is difficult even for modern workers to see the two lateral flagella in living cells, it is assumed today that Kent missed one of the four flagella that are present. Since Trimastix was the first name to be applied to these organisms, it is retained (in the language of the Codes of Nomenclature for living things, it "has priority") even though it is an inaccurate description of the species in the genus.

Kent placed a single species in the genus, T. marina Kent, 1880. This is therefore the "type" species, the principal reference point used by taxonomists to decide whether a particular species belongs in one genus or another (see below for an example of how this works).

A second species was added by A. Hollande. This species, T. convexa Hollande in Grassé, 1952, is described (in French) on p. 705 of vol. 1 of the multivolume Traité de Zoologie [Treatise on Zoology], edited by P.-P. Grassé and published in 1952.

The species Trimastix pyriformis (Klebs, 1893) Bernard, Simpson and Patterson, 1999 was first described by the German protistologist G. Klebs (in a lengthy article entitled "Flagellatenstudien" [Studies on Flagellates], published in the Zeitschrift für wissenschaftlichen Zoologie [Zoology Research Journal] in 1893). Klebs named it Tetramitus pyriformis. As Tetramitus pyriformis, it has not infrequently been named as a protozoon of sewage and sewage treatment systems. Bernard et al. (confirmed by O'Kelly et al.) found that this species more closely resembles the type species of Trimastix, T. marina, than the type species of Tetramitus, T. rostratus Perty, 1852. This observation resulted in the name change.

Provisional key to the species of Trimastix

  • 1. Cells to 30 micrometres in length; anterior flagellum tapering, thickest at the base; differentiated ingestion apparatus present; usually associated with marine habitats but also recently found in brackish and fresh waters
    .......................................... T. marina Kent, 1880
  • 1. Cells to 20 micrometres in length; anterior flagellum not tapering, of uniform thickness throughout; differentiated ingestion apparatus absent
    ...................................... T. pyriformis complex; 2.

    For information on the classification of Tetramitus, see the Classification page.

    For lookalike taxa see Similar genera.

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