Thecamonadinae

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.^[2][3]

Thecamonadinae
Scientific classification
Domain:	Eukaryota
Clade:	Amorphea
Class:	Thecomonadea
Order:	Apusomonadida
Family:	Apusomonadidae
Subfamily:	Thecamonadinae Larsen & Patterson, 1990[1] stat. nov. Heiss et al., 2015[2]
Type genus
Thecamonas Larsen & Patterson, 1990[1]
Genera
Chelonemonas Thecamonas
Synonyms
Thecamonadidae Larsen & Patterson, 1990[1]

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.^[2]

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.^[1] Posterior phylogenetic analyses showed that this family branched within Apusomonadidae, and the taxon fell out of use.^[4] 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.^[2]

Classification

As of 2022, the subfamily contains two genera, Chelonemonas and Thecamonas, and a total of 7 species.

• Chelonemonas Heiss, Lee, Ishida & Simpson, 2015^[2]

• C. dolani Torruella, Galindo et al., 2022^[3]
• C. geobuk Heiss, Lee, Ishida & Simpson, 2015^[2]
• C. masanensis Heiss, Lee, Ishida & Simpson, 2015^[2]

• Thecamonas Larsen & Patterson 1990^[1]

• T. filosa Larsen & Patterson, 1990^[1]
  = Amastigomonas filosa (Larsen & Patterson, 1990) Molina & Nerad, 1991
• T. muscula (Mylnikov, 1999) Cavalier-Smith, 2010^[4]
  = Amastigomonas muscula Mylnikov, 1999
• T. mutabilis (Griessmann, 1913) Larsen & Patterson, 1990^[3]
  = Rhynchomonas mutabilis Griessmann 1913
  = Amastigomonas mutabilis (Griessmann, 1913) Patterson & Zölffel, 1993
• T. trahens Larsen & Patterson, 1990^[3]
  = Amastigomonas trahens (Larsen & Patterson, 1990) Molina & Nerad, 1991