DESCRIPTION OF THE KINGDOM EUEXCAVATAE1
| EUKARYA> EXCAVATA> EUEXCAVATAE |
KINGDOM EUEXCAVATAE LINKS
| Euexcavatae (u-eks-ka-VA-te) is made of one Greek and two Latin roots which mean true (eu -ευ); from (ex); a cavity (cavus). The reference is to those organisms that have or are related to taxa which have a special feeding groove called an excavate. |
| INTRODUCTION TO THE KINGDOM EUEXCAVATAE The Kingdom Euexcavatae is one of two kingdoms within the Supergroup Excavata (defined as a higher level group by Cavalier-Smith 2002). These organisms are primarily unicellular, motile and range from animal symbiotes to free-living taxa. I derived this taxonomic system as a reflection of the systems of Simpson (2003) and Cavalier-Smith (2002 and 2003), both of whom group the parabasalids, metamonads, diplomonads, oxymonads, jakobids, and carpediemonads together with the discicristates. We have done that, too, but we treat both groups as kingdom-level clades that together make up the Supergroup Excavata. The synapomorphic characters that define this kingdom include multiple flagella associated with nuclei and a feeding groove, the excavate, in the cell associated with the flagellar insertions. We derived the name, Euexcavatae, meaning the “true excavates”, to describe those organisms with a depression or feeding groove located on the cell surface and associated with one or more flagella. Formerly, the major taxa in this kingdom (parabasalids, metamonads, diplomonads, and oxymonads) were considered to be among the most basal of the eukaryotes. They figured prominently in the Archezoa Hypothesis (Cavalier-Smith 1983 and Roger 1999), a view that the basal eukaryotes evolved before the acquisition of particular lines of mitochondria (platy-, disco-, and tubulocristate mitochondrial lines). Discoveries of related taxa with mitochondria and degenerate mitochondria in amitochondriate taxa helped to put the Archaezoa Hypothesis to rest. Furthermore, that almost all of the amitochondriate taxa were animal gut parasites or commensals further called into question their apparent primitive natures. Thus, the deep branching of taxa like Giardia was artifactual. When multiple tree analyses (called supergroup analyses) were produced (e.g. Baldauf 2003a), the base and crown of the eukaryotic tree disappeared and what remained was a branching pattern that resembled the petals of a flower. Furthermore, the supergroup analyses helped to resolve orphaned taxa like the free-living Jakobids and the recently-discovered Carpediemonas. Figure 1 is a cladogram that uses information from Lara et al. (2006), Kolisko et al. (2008), and Malik et al. (2011). The kingdom shows separation between the symbiotic/parasitic taxa (Eopharyngia, Parabasala, and Metamonadea) and the free-living taxa (Carpediemonada and Jakobada). |
FIGURE 1. A cladogram showing the relationships between the phyla of the Euexcavatae. The cladogram is a consensus view from Lara et al. (2006), Kolisko et al. (2008), and Malik et al. (2011).
| PHYLA OF THE KINGDOM EUEXCAVATAE |
CARPEDIEMONADA (Cavalier-Smith 2003)
JAKOBADA (Cavalier-Smith 1993)
EOPHARYNGIA (Cavalier-Smith 1993)
METAMONADA (Grasse 1952)
PARABASALA (Honigberg 1973)
| 1. We used this name to distinguish the taxa from those with discoid mitochondria within the supergroup, Excavata. The name Metamonada has been used, but it leads to confusion. |
| LITERATURE CITED Baldauf, S. L. 2003a. The deep roots of eukaryotes. Science. 300 (5626): 1701-1703. Cavalier-Smith, T. 1983. A six-kingdom classification and a unified phylogeny. In: Schenk, H. E. A. and W. S. Schwemmler, eds. Endocytobiology II. de Gruyter, Berlin. pp. 1027-1034. Cavalier-Smith, T. 2002a. The phagotrophic origin of eukaryotes and phylogenetic classification of Protozoa: International Journal of Systematic Evolutionary Microbiology. 52:297–354. Cavalier-Smith, T. 2003a. Protist phylogeny and the high-level classification of Protozoa. European Journal of Protistology. 39:338-348. Grasse´, P. P. 1952. Classe des Zooflagellata ou Zoomastigina. In: Grasse´, P. P., ed. Traite´ de zoologie, vol I (1). Masson. Paris. Honigberg, B. M. 1973. Remarks upon trichomonad affinities of certain parasitic protozoa. In Progress in Protozoology: Abstracts of Papers Read at the 4th International Congress of Protozoology, Clermont-Ferrand, 2–10 September 1973, p. 187. Edited by P. De Puytorac & J. Grain. Clermont-Ferrand: Universite´ de Clermont. Kolisko, M., I. Cepicka, V. Hampl, J. Leigh, A. J. Roger, J. Kulda, A. G. B. Simpson, and J. Flegr. 2008. Molecular phylogeny of diplomonads and enteromonads based on SSU rRNA, alpha-tubulin and HSP990 genes: implications for the evolutionary history of the double karyomastigont of diplomonads. BMC Evolutionary Biology. 8: 205 doi: 10.1186/1471-2148-8-205 Lara, E., A. Chatzinotas, and A. G. B. Simpson. 2006. Andalucia (n. gen.) – the deepest branch within jacobids (Jacobida: Excavata), based on morphological and molecular study of a new flagellate from soil. Journal of Eukayotic Microbiology. (53(2): 112-120. Malik, S-B., C. D. Brochu, I. Bilic, J. Yuan, M. Hess, J. M. Logsdon, and J. M. Carlton. 2011. Phylogeny of parasitic Parabasalia and free-living relatives inferred from conventional markers vs. Rpb1, a single-copy gene. PLoS ONE. 6(6): e20774. doi:10.1371/journal.pone.0020774 Roger, A. J. 1999. Reconstructing early events in eukaryotic evolution: American Naturalist. 154(supplement): S146–S163. Simpson, A. G. 2003. Cytoskeletal organization, phylogenetic affinities and systematics in the contentious taxon Excavata (Eukaryota). International Journal of Systematic and Evolutionary Microbiology. 53: 1759-1777. |
| By Jack R. Holt. Last revised: 02/17/2015 |
