world of amoeboid organisms

Microcometes palludosa
after Lee et al., 2005

Microcometes paludosa  Cienkowski, 1876

Observations: This genus is of uncertain affinities. Organisms with cell body 5-7 µm in diameter living in a lorica measuring 10-13 µm in diameter, the lorica organic, becoming brown with age, presumably due to accumulated metal salts. Fine, occasionally branching pseudopodia with small granules emerge from 4-8 collared apertures. With two short relatively inactive cilia that are hard to see except in cells that have settled recently and are without lorica or with a transparent lorica. With contractile vacuole, nucleus with round nucleolus.

Ecology: Freshwater. Extremely common, from Carlisle beach and Carlton River, Tasmania.

Remarks: This genus was first described by Cienkowski (1876) as an amoeba of uncertain affinities. It has been reported infrequently from Northern Europe and America (e.g. Leidy 1879, Penard 1902). It is not surprising that this organism was mistaken for an amoeba, given the difficulty of observing the cilia in all but recently settled cells. The genus has similarities with naked amoebo-ciliates having fine pseudopodia such as Massisteria (Larsen and Patterson 1990, Patterson and Fenchel 1990) and Gymnophrys (Mikrjukov and Mylnikov 1995) – but ultrastructural or molecular studies will be required to establish if Microcometes is closely related to either of these. This species has not previously been reported from Australia.

Lee, W.J., Simpson, A. G. B. and Patterson, D. J.: Free-living Heterotrophic ciliates from Freshwater Sites in Tasmania (Australia), a Field Survey Acta Protozool. (2005) 44: 321 – 350.

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