| Symbiontida | |
|---|---|
.jpg) | |
| Calkinsia aurea | |
Scientific classification | |
| Domain: | Eukaryota |
| Clade: | Discoba |
| Phylum: | Euglenozoa |
| Class: | Symbiontida Yubukiet al., 2009[1] |
| Genera | |
| Synonyms | |
| |
Symbiontida is abasalclass offlagellateEuglenozoa.[2][3] As euglenozoans may be basaleukaryotes, the Symbiontida may be key to studying the evolution ofeukaryotes, including the incorporation of eukaryotic traits such as the incorporation ofalphaproteobacterialmitochondrialendosymbionts.
Euglenozoa are a large group offlagellateDiscoba. They include a variety of common free-living species, as well as a few important parasites, some of which infect humans. Euglenozoa are represented by four major classes,i.e.,Kinetoplastea,Diplonemea,Euglenida, and Symbiontida. Euglenozoa are unicellular, mostly around 15–40 μm (0.00059–0.00157 in) in size, although some euglenids get up to 500 μm (0.020 in) long.[4]
Euglenozoa are characterized by the ultrastructure of theflagella. In addition to the normal supporting microtubules oraxoneme, each contains a rod (calledparaxonemal), which has a tubular structure in one flagellum and a latticed structure in the other. Based on this, two smaller groups are included: thediplonemids andPostgaardi.[5]
Symbiontida is a third deep-branching euglenozoanclade that may be a sister to Euglenoida but does not branch within them orGlycomonada on the evolutionary most realistic sequence trees presented in the next three sections, contrary to some poorly resolved earlier trees. They were placed in the new subphylum Postgaardia as class Postgaardea because they are radically different ultrastructurally from both euglenoids and glycomonads.[2]
Symbiontida arebiciliate free-living anaerobes covered in epibiotic bacteria in longitudinal rows are the diagnosis. A highly contractile pellicle with multiple evenly spaced microtubules and no morphogenetic pairs that are specifically distinguished. Without cytostomal or reservoir encircling fibers, cemented jaw supports, or hard longitudinal straight cemented rods, thecytopharynx is simplified. Symbiontida is the lone included class in etymology.[2]
Reconstructions of FA ultrastructure inPostgaardi andCalkinsia confirmed that they were fundamentally similar and deserved to be classified together as a distinct order Postgaardida and class Postgaardea, as both genera share six finger-like projections.[2]
According to Cavalier-Smith (2017):[6]
According to Kostygovet al. (2023):[3]
