Subfamily of flagellates
Thecamonadinae is a subfamily of heterotrophic protists. It is a monophyletic group, or clade, of apusomonads, a group of protozoa with two flagella closely related to the eukaryotic supergroup Opisthokonta. The subfamily contains two genera "Chelonemonas" and "Thecamonas", which are found in marine habitats.
Morphology.
Thecamonadinae are unicellular eukaryotes, exhibiting cells smaller than 10 μm, and an ""Amastigomonas"-type" cell body shape: plastic, oval to oblong, with a prominent proboscis that measures around ¼ of the cell body length. They have a rigid "tusk" of between 200 and 250 nm in diameter, that arises to the right of the anterior flagellum and extends around 0.5–1.0 μm. This tusk can be visible under optimal conditions of light microscopy. Aside from the flagella, they often present thin pseudopodia trailing behind the moving cell.
Systematics.
History of taxonomy.
Thecamonadinae was initially a family-level taxon, Thecamonadidae, described in 1990 by Jacob Larsen and David J. Patterson. At the time, it was composed exclusively of the genus "Thecamonas", described by the same authors. Members of this family were characterized by a mobile anterior "snout" (or "tusk"), which is superficially resembling of the flagellate "Rhynchomonas". However, their ultrastructure resembled "Apusomonas" in the pliable dorsal theca. Posterior phylogenetic analyses showed that this family branched within Apusomonadidae, and the taxon fell out of use. In 2015, Aaron A. Heiss and collaborators co-opted this taxon as a subfamily within Apusomonadidae to designate the clade uniting "Chelonemonas" and "Thecamonas". This clade is supported by multiple phylogenetic analyses and accepted as a valid taxon.
Classification.
As of 2022, the subfamily contains two genera, "Chelonemonas" and "Thecamonas", and a total of 7 species.
*"C. dolani" Torruella, Galindo et al., 2022
*"C. geobuk" Heiss, Lee, Ishida &amp; Simpson, 2015
*"C. masanensis" Heiss, Lee, Ishida &amp; Simpson, 2015
*"T. filosa" Larsen &amp; Patterson, 1990= "Amastigomonas filosa" (Larsen &amp; Patterson, 1990) Molina &amp; Nerad, 1991
*"T. muscula" (Mylnikov, 1999) Cavalier-Smith, 2010= "Amastigomonas muscula" Mylnikov, 1999
*"T. mutabilis" (Griessmann, 1913) Larsen &amp; Patterson, 1990= "Rhynchomonas mutabilis" Griessmann 1913= "Amastigomonas mutabilis" (Griessmann, 1913) Patterson &amp; Zölffel, 1993
*"T. trahens" Larsen &amp; Patterson, 1990= "Amastigomonas trahens" (Larsen &amp; Patterson, 1990) Molina &amp; Nerad, 1991
References.
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