ALVEOLATAE

Ciliata (si-le-A-ta) is derived from the Latin word for eyelash (cilium). The reference is to a cell that has short, eyelash-like flagella rather than long whip-like flagella.

The ciliates are very common and highly diverse microscopic heterotrophs in nearly all environments with liquid water (Figures A-S). Some of them are symbionts and parasites of animals. As their name implies, the ciliates bear cilia, numerous small, paired flagella with an underlying structure of basal bodies and flagellar roots (called kineties) that allow for coordinated motion of the flagella (Figure T). Almost all of them have a cytostome, and most classification systems are based on specialized ciliary and other structures associated with the cytostome (called peristomal apparatus). Most of the free-living taxa, like Paramecium (Figures O and T) feed on bacteria and have specialized ciliary regions that concentrate bacteria at the cytostome. However, some, like Dileptus (Figure F) and Bursaria (Figure K), eat whole ciliates or other things. Dileptus is particularly interesting in that it waves its proboscis about until it strikes a larger organism, which could include small animals. The proboscis has toxicysts, which can lyse cells and tissues, on its leading edge. I have watched Dileptus surround small planarians and slice them to oblivion.

A number of ciliates have become adapted to a sessile lifestyle. Some of the most common in still freshwater habitats are Vorticella and its relatives. The cell body sits atop an attached stalk and feeds as a filter-feeder. When disturbed, the myoneme in many taxa contracts and pulls the cell body to the substrate. They can release and swim away in search of food, etc. Many other taxa also are sessile and filter-feeders including Spirochona (Figure H) and Trichodina (Figure R). Suctorians (Figure H) although ciliates, do not display cilia when attached. Rather, they elaborate tentacles that have feeding disks at their ends (suctorial tentacles). When a prey item like a small ciliate contacts the disk, it stops moving and its cytoplasm is taken into the cell body of the suctorian through the tentacle. Because they have no flagella in the attached form, suctorians divide and release ciliated swarmer cells for dispersal and as gametes.

Ichthiophtherius, which literally means fish louse, lives its life as a parasite under the skin of certain fish. During that time, the lesion caused by the ciliate swells and looks like a grain of salt. Fish show discomfort and distress when infested and try to rub themselves against the bottom rocks, plants, etc. When mature, the ciliate emerges as a trophozoite and swims to the bottom where it covers itself with mucilage and divides into hundreds of offspring. The emergent tomites can swim for up to 3 days in searching for another host fish. It is during this brief free-swimming stage that they are susceptible to treatment.

Ciliates exhibit a characteristic nuclear dimorphism with diploid micronuclei and polyploid macronuclei in most vegetative cells. The macronucleus seems to operate as the nucleus in charge during most of the vegetative growth of the cell. However, the micronucleus takes over in anticipation of sexual reproduction and undergoes meiosis to form gamete nuclei. Some of the taxa, like suctorians, have more elaborate life cycles, but most conjugate and exchange haploid nuclei. The fusion product remains diploid and divides to form a macronucleus, which becomes polyploid. When cells undergo mitosis, both nuclei divide and segregate appropriately during cytokinesis.

*A. Stentor, a very large heterotrich ciliate can attach and assume the shape of a long funnel. Note the open membranelle ring around the broad cytostomal region.*	*B. Euplotes, is flattened dorsoventrally and has a terminal oral region. The cell generally is naked with irregular regions of cirri.*	*C. A lorica of Tintinnopsis,* which is made of particles glued together by the sessile ciliate. The cell attaches itself inside the lorica.**		*D. Urostyla* has cirri in zig-zag rows and a subapical oral region.**	*E. Halteria* is a planktonic cell that moves by its oral cirri. The cell mainly is naked otherwise with a few bristle-like cilia or thin cirri.**
F. Dileptus is a swan-shaped cell, the body of which is holotrichous and creeps over the substrate. The proboscis is lined with toxicysts that lyse cells, which are engulfed by a cytostome at the base of the proboscis.	*G. Balantidium* is an intestinal parasite of humans and other vertebrates. The cell is holotrichous.**	*H. Spirochona* is a sessile cell with a thin winding row of cilia on the edge of membranous flange. They reproduce by budding.**		I. A suctorian, a sessile cell that has suctorial tentacles rather than cytostomes for feeding. They reproduce by budding and form ciliated swarmer cells.	*J. Nassula* is a holotrichous cell with pronounced tubular feeding structure called cyrtos.**
*K. Bursaria* is a large holotrichous cell with a deep cytostomal cleft, along its left side is a long oral membranelle. This species feeds on other ciliates like Paramecium.**	*L. Colpoda* is an oval cell with an obvious small cytostome about midway down the cell. The cytostome has rows of small membranelles.**	*M. Prorodon* is an almost spherical cell with a terminal cytostome (at top).**		*N. Plagiopyla* is a species of anaerobic habitats. The cell is uniformly covered with monokinetids with rows of dikinetids surrounding the cytostome.**	*O. Paramecium* is a common holotrichous cell. The cytostome is found in the base of a long groove in the slipper-shaped cell.**
P. Urozona is unusual in its order in that its somatic ciliature is reduced to a central girdle. It has a trailing thigmotactic tail-like cilium.	*Q. Ichthiophtherius,* the cause of the fish disease called ich, lives under the skin of host fish and emerges as swarmer cells.**	*R. Trichodina* is a surface symbiont/parasite of fish. It has a broad oral disk surrounded by membranelles and an adhesive base.**		S. Vorticella is an attached peritrich with an oral region like that of Trichodina; however, this species has a stalk with a contractile myoneme. Note that the two cells in the center have contracted.	*T. An SEM micrograph of the somatic ciliature of Paramecium. Note the rows or kineties that wind down the cell.*
Images taken from: A,F,O: From the Systematic Biology Biodiversity Collection B&C: http://biodidac.bio.uottawa.ca/Thumbnails/ D&E,J: http://protist.i.hosei.ac.jp/PDB/Images/Ciliophora/ G: http://www.umanitoba.ca/faculties/science/zoology/faculty/dick/z346/balanhome.html H: http://www.uni-bielefeld.de/biologie/Didaktik/Zoologie/html I: http://microscope.mbl.edu/scripts/			K-N: http://microscope.mbl.edu/baypaul/microscope/ P: http://microscope.mbl.edu/scripts/microscope.php?func=imgDetail&imageID=12007 Q: http://www.vet.cornell.edu/Public/FishDisease/AquaticProg/highlights/Ich/ICH2.JPG R: http://www.uq.edu.au/nanoworld/images/mystery10t.gif S: http://www.college.ucla.edu/webproject/micro7/studentprojects7/Rader/conval_2.jpg T: Kessel and Shih (1974)

The origin of the ciliates has been equally shrouded in mystery. Corliss (1979) proposes that the gymnostome ciliates evolved from an unknown group of flagellates. Taylor (1976) suggests a strong relationship between the dinoflagellates and the ciliates. More recent evidence (Gajadhar et al. 1991; Cavalier-Smith 1993; Patterson 1999; and Taylor 1999) supports a common origin of the ciliates, Dinoflagellata, and Apicomplexata in the "supergroup" called the alveolates. The tree produced by Baldauf (2003) suggests that the ciliates are among the most primitive of the alveolates.

The systematics of the ciliates has been based on gross morphology (Margulis and Schwartz 1988 and 1998; Kudo 1966; and Grell 1976) for a very long time. More recently, some taxonomic schemes like those of Corliss (1979), Small and Lynn (1985), Sleigh et al. (1984), and Lynn and Small (1990 and 2000) differ significantly as they try to incorporate ultrastructural evidence, mainly the organization of the infraciliature and the cytostomal apparatus. The ultrastructure-based systems have grown to become almost unwieldy. The one below is taken from Lynn and Small (2000) which contains two subphyla and 10 classes. A comprehensive check on the ultrastructure is needed in this group. Because, although ultrastructure does give important fundamental similarities, at present, it is unclear whether those similarities are synapomorphies or symplesiomorphies. With that warning, I offer the system of Lynn and Small (2000).

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