Family Mesofilidae Cavalier-Smith and Bass 2009

Diagnosis: Biciliate amoeboflagellates with numerous extremely long branching filopodia that in contrast to Heliomorphidae (Tetradimorpha and Heliomorpha — usually known by the invalid names Dimorpha or Dimorphiella) do not radiate in three dimensions from a centrosome but are appressed to the substratum during feeding. Filopodia and long cilia can be present simultaneously or each on their own, depending on the growth phase.

Type genus Mesofila Cavalier-Smith and Bass 2012

Diagnosis as for family Mesofilidae.

Mesofila limnetica Cavalier-Smith and Bass 2009

Diagnosis: With amoeboid and ciliate phases. Amoeboid cells circular to slightly polygonal, with uneven/pitted surface; 9—14 µm in diameter. Central nucleus about a quarter of cell body diameter, with conspicuous central nucleolus. Branching filopodia issue from all around the cell, sometimes with slightly thicker filopodia emerging bipolarly. Filopodia long, up to 10x cell diameter; or more. Cell body and filopodia remain in contact with the substrate; immotile, except in motile ciliate stage. Filopodia carry evenly and closely spaced prominent granules, and sometimes appear to anastomose. The ovoid ciliate, cell length 8 µm) has two cilia, the posterior trailing and 2-2.5x cell length, the anterior 0.5-1x body length beats vigorously, often curving round on it self. Gliding erratic and swift, with the (thicker) posterior end of the cell raised off the substrate. Ciliate also swims rapidly with a helical motion. Cysts spherical, smooth, refractive; ca. 10 µm diameter. Can grow very densely, especially when bacterial density high, and bacteria accumulate and obscure the cellbody.

Type locality: hotspring with rich organic mud from stream, Palm Canyon, California, United States.

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