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Massisteria spec. Fresh water; cilia are arrowed

Genus Massisteria Patterson & Fenchel, 1990

Diagnosis: small body, usually under 5 µm, which in trophic organisms emits curving, sometimes branched fine pseudopodia with extrusomes, and have two cilia lying inactive over the body surface. Under some circumstances, the arms may be resorbed and the organism will swim actively. Trophont does not move actively, feeds usually on bacteria. Multicellular forms are encountered.

Type species: Massisteria marina Larsen and Patterson, 1990

Remarks: This genus has only been reported from marine sites all over the world, but recently (2012) I found specimens in moist-chamber-mounts from fresh water samples (see the photomicrographs here) which closely resemble Massisteria. These specimens seem to live inside a kind of shell which is hard to detect light microscopically. Probably they represent a Microcometes species. The resemblance between Massisteria and Microcometes has also been noted by Lee et al (2005). The only difference at light microscopic level is the presence of a shell in Microcometes.
Specimens of Massisteria are light microscopically very similar to Limnofila. The only distinction seems to be the presence or absence of the two cilia.

Massisteria marina Larsen and Patterson 1990

Diagnosis: Organism with an irregular star-shaped body from which radiate thin pseudopodia with extrusomes. There are 2 inactive flagella. The organism is normally sedentary but, under adverse conditions, the arms are resorbed, the flagella become active, and the organism becomes a motile non-feeding flagellate.

Remarks: This small phagotrophic protist is associated with sediment particles and with suspended detrital material in littoral and oceanic marine waters. It has been found at sites around the world.

Literature: Patterson, D. J. and Fenchel, T.: Massisteria marina Larsen and Patterson 1990, a widespread and abundant bacterivorous protist associated with marine detritus. – Marine ecology progress series. Oldendorf  Vol. 62, no. 1-2, pp. 11-19. 1990.

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