EUEXCAVATAE

SYSTEMATIC BIOLOGY					THE EUEXCAVATAE
HOME	SYLLABUS	WEEKLY ASSIGNMENTS	J. SYSTEMATIC BIOLOGY	TAXA OF LIFE
PHYLUM EOPHYRINGA

INTRODUCTION TO THE EOPHYRINGA

Eophyringa (e-o-fi-RIN-ga) is made from a Greek and a Sanskrit word meaning before (eos -έως) and syphilis (phyringa a Sanskrit word).

The eophyringids include Giardia and Chilomastix (Figures A-C), taxa that are of some economic importance. Giardiasis is among the most common diseases from drinking contaminated water in the United States. In high rates of infection, Giardia can coat the mucosa of the small intestine and inhibit the absorption of certain nutrients like vitamin B-12. Most of the known members of this phylum are parasites or commensals, though some are free-living. All members are amitochondriate and motile with four to six flagella, one of which is recurrent and associated with the excavate. Part of their success as parasites comes from their ability to reproduce (asexually) by producing a resistant cyst.

A. High magnification micrograph of a Giardia trophozoite from a fecal sample.

B. An SEM micrograph of two Giardia trophozoites attached to intestinal mucosa.

C. Chilomastix trophozoite.

Images taken from:
A: http://www.biosci.ohio-state.edu/~parasite/giardia.html
B: http://www.uiowa.edu/~cemrf/archive/sem/large/Giardia.gif
C: http://microscope.mbl.edu/baypaul/microscope/images/t_imgAZ/chilomastix_atw.jpg

SYNOPTIC DESCRIPTION OF THE EOPHYRINGA

The following descriptions come from Vickerman (1990), Brugerolle and Mignot (1990), Dyer (1990d), Lee et al. (1985), Grell (1976), Kudo (1966), Patterson (1999), Taylor (1999), and Cavalier-Smith (2003).

I. SYNONYMS: diplomonads, retortomonads.

II. NUMBER: likely no more than 100 species.

III. PHYLUM CHARACTERISTICS:

A. Structure and Physiology

Cell Form: Unicellular.

Flagella: Occur in groups of four or six; usually one of which is recurrent. Flagella inserted anterior to excavate feeding groove, when present. Recurrent flagella without vanes.

Basal Bodies: Basal bodies cruciate; rootlets from the basal bodies form bundles passing into the cytoplasm, and microtubular and/or striated roots connect the basal bodies to the nucleus thus forming a karyomastigont unit.

Cell Covering: Naked but pellicular microtubules may be present and support edges of the feeding groove. The groove in some is pronounced and forms a deep crypt or pocket. In many taxa, the karyomastigonts and grooves are doubled (thus the name diplomonad).

Chloroplasts: Not present.

Food Reserves: ?

Mitochondria: Not present.

Golgi: Present in retortomonads only, but no particular association with the nucleus or the flagellar roots.

Nucleus: Connected to basal bodies via basal body roots to form a karyomastigont unit; four or six flagellar basal bodies associated with a nucleus.

Centrioles: Not reported.

Inclusions and Ejectile Organelles:Food vacuoles.

B. Mitosis, Meiosis and Life History

MITOSIS: Intranuclear spindle.

MEIOSIS: Presumed.

SEXUAL REPRODUCTION AND LIFE HISTORY: ?

C. Ecology: Mostly commensals and parasites of animal digestive tracts. Some free-living.

SYSTEMATICS OF THE EOPHYRINGA

The eophyringids include Giardia and Chilomastix (Figures A-C), taxa with very deep branching when compared with other eukaryotes using single gene or small ribosomal RNA comparisons. Thus, those taxa and their related genera seemed to be among the most primitive of all living eukaryotes. The main problem with such a scenario is that eophyringids like Giardia and Chilomastix inhabit the gut. Secondary simplification and loss of mitochondria seem to be common in such lines. Supergroup analyses of the type presented by Baldauf (2003), however, showed that members of this group were not diffuse up a eukaryotic tree of life but part of a coherent branch called the excavates that included trichomonads, parabasalids, jakobids, and metamonads.

HIERARCHICAL CLASSIFICATION OF THE EOPHYRINGA

The general organization of the following taxonomy was influenced by Cavalier-Smith (2003), Patterson (1999), and Taylor (1999).

CLASS TREPOMONADEA

Mainly diplomonads (paired karyomastigonts and feeding grooves); no golgi; some with cytoplasmic suckers and internal ribbon-like microtubular flagellar roots.

ORDER DISTOMONATIDA

Cytostomes lateral or posterior.

Trepomonas, Hexamita, Spironucleus.

ORDER GIARIIDA

Cytostomes absent.

Giardia, Octomitus.

ORDER ENTEROMONADIDA

Karyomastigonts not in pairs, cytostome in anterior part of cell.

Enteromonas, Trimitus, Caviomonas.

CLASS RETORTOMONADEA

Four or six flagella inserted at the apical end of the cell; basal bodies directly associated with the surface of the nucleus. Recurrent flagellum lies in apical groove that is deep and pouch-like. A single order (RETORTOMONADIDA).

Chilomastix, Retortomonas, Cochlosoma.

This page is maintained by Jack R. Holt. Last revised 02/07/2008.