INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

PROTISTS - PROTISTA

PROTOZOANS (PROTOZOA)

ALVEOLATES

PHYLUM CILIATED PROTOZOA, OR CILIATES (CILIOPHORA)

CLASS POLYHYMENOPHOREA

Polyhymenophoreans are characterized by a clockwise-coiled adoral membranelle zone leading to the cytostome. In addition, they possess cilia that either uniformly cover the entire body or form various cirri located predominantly on the ventral side of The Cell.

The order Heterotrichida is characterized by Two Types of cilia: fine cilia covering the entire body and large ones grouped into membranelles forming an adoral zone. These are free-living, predominantly planktonic forms, less commonly sessile or benthic. This group includes quite large Ciliates reaching 2-3 mm in size, such as the trumpet animalcule (Stentor), which has a funnel-shaped body with a stalk at the posterior end that allows the animal to temporarily attach to the substrate (Fig. 31, g), as well as the oval Bursaria truncatella and worm-like species of the genus Spirostomum (Fig. 31, d, e). All of them feed on Bacteria. Sessile species (genus Eufolliculina, etc.) inhabit specialized loricae made of organic matter secreted by their Cells.

The order Hypotrichida comprises ciliates with a dorsoventrally flattened cell. Robust cirri are located on the ventral side of the cell, enabling it to "crawl" along the substrate. There is also an adoral membranelle zone around the cytostome and small dorsal cilia. This order includes, for example, the fairly large (0.3 mm) freshwater Ciliate Stylonichia mytilus, which feeds on bacteria and small Protozoans (Fig. 31, e).

Ciliates occupy an important place in ecosystems. In aquatic environments, they play a major role in food webs as consumers of bacteria and certain Algae, while serving as food for numerous invertebrates and fish fry. Soil ciliates secrete substances that stimulate the reproduction of bacteria, including nitrogen-fixing ones, thereby contributing to increased soil fertility. Many ciliate species have transitioned to exo- or endobiosis (living on the body surface or within the Internal Organs of a host). However, most of them feed primarily on bacteria rather than host Tissues. The number of species that are true parasites is negligible.