Limnofila

Clathrulina elegans
Limnofila spec., 11 µm, peat bog.
Genus Limnofila Cavalier-Smith and Bass, 2009

Diagnosis: trophic phase a small, often globular cell; cilia if present generally not visible in the light microscope; with branched regularly granular and very slender, exceedingly thin thread-like filopodia. Bacterivorous. Freshwater.
Type spe­cies Limnofila borokensis Cavalier-Smith and Brass, 2009.

Remarks: ultrastructurally studied species (borokensis and mylnikovi) have flat mitochondrial cristae, bundles of 2—6 microtubules supporting the filopodia, complex concentric-structured extrusomes, two ciliary stubs with transverse plate at the base of the transitional region but no 9+2 axoneme, no obvious paranuclear microbody, no prominent centrosome (unlike Heliomonadida), and no large granules in the distal centriolar matrix. Nuclear division closed pleuromitosis with extranuclear spindle.

Five known species:

Limnofila borokensis Cavalier-Smith and Bass, 2009

Diagnosis: three distinct forms in addition to smooth spherical cysts (2.5-3.5 µm diameter); stationary feeding stage with central cell body (5-7 µm) and 2-13 radiating, extremely slender branching filopodia (0.15 µm thick) with extrusomes along their length (3-4 x cell body); creeping stage polarised, with lobopodia at the leading edge and sparse trailing filopodia; brief non-feeding flagellate phase (13-15 µm x 3-4 µm) with no pseudopodia and very few extrusomes has a short motile laterally beating anterior cilium and 13-15µm trailing cilium; several contractile vacuoles in cell body.

Limnofila mylnikovi Cavalier-Smith and Bass, 2009

Diagnosis: cell body 5-6.6 µm, branched filopodia 1-4 x body length; unlike L. borokensis lacks swimming biflagellate stage or mobile lobopodia-driven amoeboid stage and cysts in cultures; single contractile vacuole; forms cell clusters in rows.

Limnofila oxoniensis Bass and Cavalier-Smith, 2009

Diagnosis: cell bodies (7-25 µm) roughly elliptical or often irregular with polygonal outline; often in pairs or small clusters, or aligned longitudinally, connected (or apparently so) via filopodia; extremely slender filopodia extend from the cell, often most prominently from the longitudinal apices, sometimes radiate more evenly though not so regularly as to confer radial symmetry. Filopodia several to 10 x body length; attached to substrate; often branched, sometimes apparently anastomosing, granular, often heavily; granules often motionless but can move slowly along them. Filopodia decrease in thickness and visibility with increasing distance from the cell body; distally -0.1 µm wide, visible only under excellent optics; movement of cell bodies across substrate very rare or indiscernible. No flagellate phase or cysts.

Limnofila anglica Bass and Cavalier-Smith, 2009

Diagnosis: Cells roughly ovoid to circular, usually with a slightly angular outline, 5-7 µm in diameter, 6-10 branching filopodia of varying lengths (2-8 times cell diameter) emerge from the cell body, sometimes but not always at radially regular intervals and extend along the substrate. Filopodia carry large granules, evenly spaced at intervals usually less than cell diameter; no anastomosis. Cell and filopodia in contact with substrate. Cells immotile and solitary; no flagellate stage or cysts seen.

Limnofila longa Bass and Cavalier-Smith, 2009

Diagnosis: Cells roughly ovoid to circular, usually with a slightly angular outline, 6-12 µm in diameter. 2/3-5 long filopodia of varying lengths (5-20 times cell diameter) emerge from the cell body, sometimes at radially regular intervals; branch more than in L. anglica; no anastomosis. Filopodial granules not as evenly spaced as in L. anglica; can differ strongly in density- spacing often at intervals equal to or greater than cell diameter. Cell and filopodia remain in contact with substrate; immotile and solitary; no flagellate stage or cysts seen.