DESCRIPTION OF THE KINGDOM DISCICRISTATAE (CAVALIER-SMITH 1998)
| EUKARYA> EXCAVATA> DISCICRISTATAE |
KINGDOM DICICRISTATAE LINKS
| Discicristatae (dis-ke-kris-TA-tee) is derived from the combination of two roots, one Greek and one Latin, that mean “discoid” (diskoides -δισκοειδής ) and “crest” (crista). The reference is to the disk-like internal crest-like membranes in the mitochondrion. |
| INTRODUCTION TO THE KINGDOM DISCICRISTATAE This taxonomic system groups the kinetoplastids, euglenoids, amoeboflagellates, stephanopogonids, and some of the cellular slime molds together in one kingdom within the supergroup Excavata. Molecular and ultrastructural data suggest that these occupy a single clade and should be grouped together as a coherent lineage (e.g. Baldauf 2003a). Taxa in this kingdom have mitochondria with distinctive discoid cristae, and the basal bodies (kinetosomes) are paired and parallel. Although many produce asexual structures and have variable forms through elaborate life cycles, they do not undergo sexual reproduction. They are sisters to the Kingdom Euexcavata and share the Supergroup Excavata in that some taxa possess the excavate feeding groove. The kinetoplastids and euglenoids have long been recognized to bear clear synapomorphies (Margulis and Schwartz 1998; Sleigh et al. 1984, Vickerman 1990b; Lee and Hunter 1985; Patterson 1999; and Taylor 1999). They all have an anteriorly-directed crypt from whose base emerges the flagella (usually 2 that are heteromorphic and heterodynamic). The anteriorly-directed flagellum is tinsel and has a paraflagellar rod that lies next to the 9+2 microtubular array. Patterson (1999) indicates that the paraflagellar rod is tubular and that the other flagellum has a lattice-like structure. The cell covering is a complex vesiculate pellicle. Cavalier-Smith (1981) refers to the clade that includes Euglenida, Diplonemea, and Kinetoplastea as the Euglenozoa. Though the three groups together seem to be monophyletic, relationships between the taxa are unclear and every possible topology of the three taxa has been proposed (von der Heyden et al. 2004; Marin et al. 2003; Simpson and Patterson 2006; Preisfeld et al. 2001; see Figure 1) This system represents a modification of Margulis and Schwartz (1998), Patterson (1999), Taylor (1999), and Cavalier-Smith (2003a). More recent interpretations of molecular and ultrastructural evidences suggest that some of the jakobids might belong in this kingdom. Furthermore, the supergroup analyses hint at an association with the cryptomonads and haptomonads (Baldauf 2003a). Thus, we consider this system as a work in progress. |
FIGURE 1. A. Cladograms of the phyla in the Discicristatae (taxa in shaded box). EZ is the Euglenozoa clade with a topology defined by the analyses of Von der Heyden et al. (2004) and Marin et al. (2003). B. A cladogram showing the taxa of the Euglenozoa clade in a topology suggested by the work of Simpson and Patterson (2006). C. Topology of the Euglenozoa clade according to Preisfeld et al. (2001).
| PHYLA OF THE KINGDOM DISCICRISTATAE |
PSEUDOCILIATA (Cavalier-Smith 1993)
HETEROLOBOSEA (Page and Blanton 1985)- CLADE EUGLENOZOA (Cavalier-Smith 1981)
- EUGLENIDA (Butschli 1884)
DIPLONEMEA (Cavalier-Smith 1993)
KINETOPLASTEA (Honigberg 1963)
| LITERATURE CITED Baldauf, S. L. 2003a. The deep roots of eukaryotes. Science. 300 (5626): 1701-1703. Cavalier-Smith, T. 2003a. Protist phylogeny and the high-level classification of Protozoa. European Journal of Protistology. 39:338-348. Lee, J. J. and S. H. Hunter. 1985. Kinetoplastida. In: Lee, J.J., S.H. Hunter, and E.C. Bovee, eds. An Illustrated Guide to the Protozoa. Allen Press. Lawrence, Kansas. pp. 141-155. Margulis, L. and K. Schwartz. 1998. Five kingdoms, an illustrated guide to the phyla of life on earth. 3rd Edition. W. H. Freeman and Company. New York. Page, F. C. and R. L. Blanton. 1985. The Heterolobosea (Sarcodina: Rhizopoda), a new class uniting Schizopyrenida and the Acrasidae (Acrasida). Protostologica. 21:121-132. Patterson, D. J. 1999. The diversity of eukaryotes. American Naturalist. 154 (Suppl.): S96–S124. Sleigh, M. A., J. D. Dodge and D. J. Patterson. 1984. Kingdom Protista. In: Barnes, R.K.S., ed. A Synoptic Classification of Living Organisms. Sinauer Associates, Inc. Sunderland , Mass. Taylor, F. J. R. 1999. Ultrastructure as a control for protistan molecular phylogeny. The American Naturalist. 154(supplement): S125-S136. Vickerman, K. 1990b. Kinetoplastida. In: Margulis, L., J. O. Corliss, M. Melkonian, and D. J. Chapman, eds. 1990. Handbook of the Protoctista; the structure, cultivation, habits and life histories of the eukaryotic microorganisms and their descendants exclusive of animals, plants and fungi. Jones and Bartlett Publishers. Boston. pp. 218-238. |
| By Jack R. Holt. Last revised: 02/12/2014 |
