| Rigifila | |
|---|---|
Scientific classification | |
| Clade: | CRuMs |
| Class: | Hilomonadea |
| Order: | Rigifilida |
| Family: | Rigifilidae Yabuki & Cavalier-Smith 2012 |
| Genus: | Rigifila Yabuki & Cavalier-Smith 2012 |
| Species: | R. ramosa |
| Binomial name | |
| Rigifila ramosa Yabuki & Cavalier-Smith 2012[1] | |
Rigifila (from Latin rigidus 'stiff' and filum 'thread') is agenus of free-livingsingle-celledeukaryotes, orprotists, containing the solespeciesRigifila ramosa (from Latin ramosus 'branched'). It is classified within the monotypic familyRigifilidae. Along withMicronucleariidae, it is a member ofRigifilida, an order ofbasal eukaryotes within theCRuMs clade. It differs fromMicronuclearia by having two proteic layers surrounding theircytoplasm instead of a single one, and having more irregularmitochondrial cristae, among other morphological differences.
The name of this genus is derived from Latin rigidus 'stiff', referring to the rigid thecell body due to their submembrane proteic layers, andfilum 'thread', referring to thefilopodia (thin thread-likepseudopodia). The speciesepithet is derived from Latin ramosus 'branched', referring to the branched filopodia exhibited by the organism.[1]
The speciesRigifila ramosa was described in 2012 by biologists Akinori Yabuki, Ken-Ichiro Ishida andThomas Cavalier-Smith from freshwater amoebae isolated in anIndianpaddy field water sample. Although they presented a similar structure toMicronuclearia, unique morphological differences and phylogenetic position of these newly discovered amoebae led to the creation of a separate genus,Rigifila, and a separate family,Rigifilidae.[1]
In addition, a new orderRigifilida was described to group the two similar organisms,Rigifila andMicronuclearia. This order was placed withinHilomonadea, a class which previously includedPlanomonadida but wasemended to only include Rigifilida.[1][2] Hilomonadea is currently considered one of the three clades ofCRuMs, a basal eukaryotic clade closely related toAmorphea, the clade containingAmoebozoa andOpisthokonta.[3]
Rigifila areunicellularprotozoa. As all members ofRigifilida, they lackcilia, but generate slender branchingfilopodia that can attach to the substrate. These filopodia lack anymicrotubules orextrusomes, and arise from the ventral side of the cell through a common filopodial stem, which is surrounded by an aperture. Under the cell membrane, they present a double-layeredproteinaceous lamina (or pellicle) that covers the whole cell body, making it rigid except for the ventral aperture. They have onenucleus on the dorsal side of the cell.[1]
Rigifila, and by extension all of Rigifilidae, differs fromMicronucleariidae by having two pellicular dense layers, as opposed to a single-layered pellicle. In addition, they exhibit several broad microtubular bands, of around 20 microtubules each, underneath the dorsal and lateral pellicle,[1] whileMicronuclearia lost all cytoplasmic microtubules.Mitochondrial cristae are completely flat inMicronuclearia, but partially flat and partially inflated inRigifila.[2]
Rigifila are free-livingphagotrophic organisms. They feed onbacteria, which they collect with theirfilopodia and ingest at the base of a ventral collar or aperture that surrounds the base of the filopodial stem.[1]