TAXA OF LIFE

DISCICRISTATAE-ICON.gif (51231 bytes)
 EXCAVATA

KINGDOM DISCICRISTATAE

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 are parallel.  Although many produce asexual structures and 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.   

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, I present this system as a work in progress.

For a discussion of the relationship between the discicristates and the other kingdoms of the Eukarya, go to the Domain Eukarya Page.

PHYLA OF THE DISCICRISTATAE

EUGLENOIDA

DIPLONEMIDA

KINETOPLASTA

HETEROLOBOSA

PSEUDOCILIATA

A photomicrograph of Euglena taken at 400X with a DIC microscope.

A more complete taxonomy (to the ordinal level) of the Kingdom Discicristatae.

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.

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: 02/15/2009