DIVERSITY OF LIFE

DESCRIPTION OF THE PHYLUM METAMONADA (GRASSE/ 1952)

EUKARYA>EXCAVATA>EUEXCAVATA>METAMONADA

Metamonada (me-ta-mo-NA-da) is made from two Latin roots that mean change (meta); and unit (monus).  The reference is to the variation in form that some cells can exhibit.

 

INTRODUCTION TO THE METAMONADA

The metamonads occupy a large group of multiflagellated cells which are parasites or commensals of the guts of insects.  Their flagella occur in groups of four, usually with 3 directed anteriorly and the fourth directed posteriorly (recurrent).  The metamonads are made of 2 major groups.  The trimastigids, represented by Trimastix (Figure 1), have only one set of flagella while the oxymonads have multiple sets of flagella and most have an anterior proboscis (Figure 2).  Both groups have a longitudinal internal cable made of the microtubular flagellar roots woven into an elongate axostyle

We defined the metamonads as those organisms having one to many karyomastigonts without parabasal bodies as did Margulis and Schwartz (1988) and Sleigh et al. (1984) who considered the organisms to be a coherent group.  The taxonomy of this group has been in flux for many years.   Lee et al. (1985) lumped the metamonads together with the parabasalids (and other flagellated unicells) as did Margulis and Schwartz (1988) and Margulis et al. (1990) who regarded the metamonads as part of a large, heterogeneous collection of flagellated organisms called the "Zoomastigina".  Later, Margulis and Schwartz (1998) grouped these with other amitochondriates in a large, diverse phylum called Archaeprotista. Earlier, Sleigh et al. (1984) raised the classes of the "Zoomastigina" to the phylum level in recognition of their disparity in structure.  Taylor (1976) showed that the metamonads were allied with the parabasalids all of which he supposed had a loose association with the chrysophytes.   Tudge (2000) considered this phylum to arise from the very base of the Eukaryote Domain.  This view was supported by the Roger (1999) modification of the Archezoa Hypothesis.  However work summarized by Baldauf (2003a, 2008) presents a consensus view based on molecular and ultrastructural characters in which this group is no longer considered primitive.  In this system, the metamonads (trimastigids and pyrsonymphids; Figures 1 and 2) are considered part of a natural group called the excavates which includes the parabasalids.  

The phylum as it is defined here is a modification of Cavalier-Smith (2003a and 2003b) and Simpson (2003).  Figure 3 shows the metamonads as part of a clade of symbiotic unicells.  The basal position is tentative and our interpretation of Lara et al. (2006), Kolisko et al. (2008), and Malik et al. (2011).


FIGURE 1


FIGURE 2

 

FIGURE 3. A cladogram showing the relationships between the phyla of the Euexcavatae (taxa in bold).  The metamonads (in the shaded box) are part of the symbiotic clade.  The relationships given here have been inferred from Lara et al. (2006), Kolisko et al. (2008), and Malik et al. (2011).

 

 
FURTHER READING:

DISCOVERY OF THE DOMAINS OF LIFE

INTRODUCTION TO THE DOMAIN EUKARYA

 

LITERATURE CITED

Baldauf, S. L. 2003a. The deep roots of eukaryotes. Science. 300 (5626): 1701-1703.

Baldauf, S. 2008. An overview of the phylogeny and diversity of eukaryotes. Journal of Systematics and Evolution. 46(3): 263-273.

Brugerolle, G., and J. P. Mignot. 1990. Retortamonadida. 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. 259-265.

Cavalier-Smith, T. 2003a. Protist phylogeny and the high-level classification of Protozoa. European Journal of Protistology. 39:338-348.

Cavalier-Smith, T. 2003b. The excavate protozoan phyla Metamonada Grasse emend. (Anaeromonadea, Parabasalia, Carpediemonas, Eopharyngia) and Loukozoa emend. (Jakobea, Malawimonas): their evolutionary affinities and new higher taxa. International Journal of Systematic and Evolutionary Microbiology. 53:1741-1758.

 Dyer, B. D. 1990c. Parabasalia. 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. 252-258. 

Grasse´, P. P. 1952. Classe des Zooflagellata ou Zoomastigina. In: Grasse´, P. P., ed. Traite´ de zoologie, vol I (1). Masson. Paris.

Grell, K. G. 1973. Protozoology. Springer-Verlag. New York.

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

Kudo, R.R. 1966. Protozoology. 5th ed. Charles C. Thomas Publisher. Springfield.

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.

Lee, J. J. 1985. Order Retortamonadida. In: Lee, J.J., S.H. Hunter, and E.C. Bovee, eds. An Illustrated Guide to the Protozoa. Allen Press.  Lawrence , Kansas. pp. 118-119.

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

Margulis, L. and K. Schwartz. 1988. Five kingdoms, an illustrated guide to the phyla of life on earth. 2nd Edition. W.H. Freeman and Co.  New York. 

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.

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. 

Patterson, D. J. 1999. The diversity of eukaryotes. American Naturalist. 154 (Suppl.): S96–S124.,

Simpson, A. G. B. 2003. Cytoskeletal organization, phylogenetic affinities and systematics in the contentious taxon Excavata (Eukaryota). International Journal of Systematic and Evolutionary Microbiology. 53: 1759-1777.

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. 1990a. Diplomonadida. 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. 200-210.

 

By Jack R. Holt.  Last revised: 02/17/2014