The glissomonads are a group of bacterivorousglidingflagellated protists that compose the orderGlissomonadida, in the amoeboflagellate phylum Cercozoa.[1] They comprise a vast, largely undescribed diversity of soil and freshwater organisms.[3] They are the sister group to cercomonads; the two orders form a solid clade of gliding soil-dwelling flagellates called Pediglissa.[2]
Morphology
External appearance
Glissomonads are zooflagellates that aren't strongly amoeboid, and are only covered by a plasma membrane. Their common ancestor is thought to be a biflagellate, with a short anteriorflagellum and a long posterior flagellum, that glided on the substrate by moving their posterior flagellum. In gliding descendants, the cell's posterior zone is usually rounded, giving the cell an ovoid shape. Some species may temporarily extend a protoplasmic tail, that unlike most cercomonads doesn't trail along the posterior flagellum.[1] At least two genera, Orciraptor and Viridiraptor, are capable of transforming into a distinctly amoeboid state attached to the surface.[4]
The group also includes descendants that have lost their gliding, mainly Proleptomonas. This genus has another exception to the group: an anterior flagellum that is longer than the posterior, while the posterior is adherent to the cell and not used for gliding.[1]
Internal structure
Most species lack obvious morphological specializations: there is no cytopharynx, deep flagellar groove, or pocket evident. Apart from Proleptomonas, which is exceptionally elongated and has a modified cytoskeleton, the nucleus is usually anterior and attached to the kinetid (= flagellar apparatus) through well-developed fibrous roots. There are typically two posterior and one anterior microtubularcentriolar roots. A contractile vacuole is usually seen in the cell's posterior area. The mitochondria have tubular cristae. There is a microbody attached to the posterior side of the nucleus, except in Proleptomonas. The Golgi apparatus is usually seen associated with the nucleus, which doesn't happen in all cercozoans.[1]
Both flagella have the same thickness and are simple, without a paraxonemal rod, hairs or scales, sometimes acronematic (= with an acroneme). Unlike in cercomonads, the ciliary transition zone has a dense transverse plate at the distal end. The anterior flagellum beats like a cilium towards the left, as seen in cercomonads, and is sometimes reduced to a short stub without an axoneme.[1]
^ abHowe AT, Bass D, Chao EE, Cavalier-Smith T (2011). "New Genera, Species, and Improved Phylogeny of Glissomonadida (Cercozoa)". Protist. 162 (5): 710–722. doi:10.1016/j.protis.2011.06.002. ISSN1434-4610.
^Hess S, Melkonian M (2013). "The Mystery of Clade X: Orciraptor gen. nov. and Viridiraptor gen. nov. are Highly Specialised, Algivorous Amoeboflagellates (Glissomonadida, Cercozoa)". Protist. 164 (5): 706–747. doi:10.1016/j.protis.2013.07.003. ISSN1434-4610.
^ abFeng, Jian-Ju; He, Chen-Yang; Jiang, Shu-Hua; Zhang, Tao; Yu, Li-Yan (2021). "Saccharomycomorpha psychra n. g., n. sp., a Novel Member of Glissmonadida (Cercozoa) Isolated from Arctic and Antarctica". Journal of Eukaryotic Microbiology. 68 (3). doi:10.1111/jeu.12840.