DESCRIPTION OF THE PHYLUM PSEUDOCILIATA (CAVALIER-SMITH 1993)
| EUKARYA> EXCAVATA> DISCICRISTATAE> PSEUDOCILIATA |
PSEUDOCILIATA LINKS
| Pseudociliata (su-do-sil-i-A-ta) is made of two roots, one Greek and the other Latin that mean false (pseudos -ψευδής) and eyelash ( cilium (text with tooltip) Cilia are eukaryotic flagella that operate by coordinated beats relative to each other. Structurally, cilia and flagella are identical (i.e. 9+2 axoneme from a basal body with associated flagellar roots). Usually cilia are shorter and more numerous than typical flagella. Also, they have an underlying structure of flagellar roots (kineties) that allow for coordination of the flagella. ). The reference here is to a cell covered by small coordinated flagella (cilia), but unrelated to the Chromalveolate group called the Ciliophora. |
| INTRODUCTION TO THE PSEUDOCILIATA This “phylum” includes a single genus, Stephanopogon, with only 4 species. These cells superficially resemble ciliates, and thus they are called Pseudociliates. Like the ciliates, they are covered with flagella that are arranged in rows of furrows or kineties (text with tooltip) Kineties (kinety) provide the underlying structure of flagellar roots found in ciliates (and others like the pseudociliata) and allow for coordination of the flagella. (Figures 1 and 2), but the flagella are not paired. They have a large apical cytostome (text with tooltip) Cytostome (literally cell mouth) is a permanent opening into the cell into which food particles move and are incorporated into food vacuoles. (Figure 1) that sometimes has associated barbs. They can be found swimming and feeding among debris in marine benthic environments. From the time of its discovery, Stephanopogon was considered to be a gymnostome ciliate (Corliss 1990). Then, the stephanopogonid ciliate affiliation began to be questioned because they had only a single type of nucleus and ultrastructural studies (Lipscomb and Corliss 1982) showed that they did not have any of the signature ciliate ultrastructural characters. However, the occurrence of discoid cristae began to link it with euglenoids, a most unexpected result. Patterson and Brugerolle (1988) examined the “ciliate-like flagellar structures and their placement in interconnected rows or kineties. Each isolated flagellar base (the flagella do not come in pairs) has a basal body that is connected by a microtubular conical basket to bands that underlie the cell surface (Patterson 1999). Cavalier-Smith (2003a) grouped the stephanopogonids together with the Heterolobosa, an action that seems more likely given the analysis of Panek et al. (2011) who show the pseudociliates emerging within a clade that includes Percolomonas (see Figure 5 of the Phylum Heterolobosa). Tentatively, we have kept the group separate with uncertain affiliations within the Kingdom Discicristatae. We treat is as a basal group within the Discicristatae (see Figure 3). |
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| FIGURE 1. A DIC micrograph of Stephanopogon. Image from http://microscope.mbl.edu/scripts/microscope.php?func=imgDetail&imageID=779 | FIGURE 2. An SEM micrograph of Stephanopogon showing the cytostome and longitudinal grooves from which the flagella emerge. Image from http://cgdc3.igmors.u-psud.fr/microbiologie/pseudocilies_fichiers/image002.jpg |
 | FIGURE 3. Cladogram of the phyla in the Discicristatae that highlights the Pseudociliata (taxon 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). |
| LITERATURE CITED Cavalier-Smith, T. 2003a. Protist phylogeny and the high-level classification of Protozoa. European Journal of Protistology. 39:338-348. Corliss, J. O. 1990. Opalinta. 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. 239-245. Lipscomb, D. L. and J. O. Corliss. 1982. Stephanopogon, a phylogenetically important “ciliate,” shown by ultrastructural studies to be a flagellate. Science. 215(4530): 303 – 304. Patterson, D. J. 1999. The diversity of eukaryotes. American Naturalist. 154 (Suppl.): S96–S124. [C,L] |
| By Jack R. Holt. Last revised: 02/17/2014 |
