The Phyllopharyngea are a class of

ciliate The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagellum, eukaryotic flagella, but are in general shorter and present in much larger numbers, with a ...

s, some of which are extremely specialized. Motile cells typically have cilia restricted to the ventral surface, or some part thereof, arising from monokinetids with a characteristic ultrastructure. In both chonotrichs and suctoria, however, only newly formed cells are motile and the sessile adults have undergone considerable modifications of form and appearance. Chonotrichs, found mainly on

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s, are vase-shaped, with cilia restricted to a funnel leading down into the mouth. Mature suctorians lack cilia altogether, and initially were not classified as ciliates. The mouths of Phyllopharyngea are characteristically surrounded by

microtubular Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nanometer, nm and have an inner diameter bet ...

ribbons, called ''phyllae''. Nematodesmata, rods found in several other classes of ciliates, occur among the subclass Phyllopharyngia, most of which are free-living. In others, the mouth is often modified to form an extensible tentacle, with toxic extrusomes at the tip. These are especially characteristic of the suctoria, which feed upon other ciliates, and are unique among them in having multiple mouths on each cell. They are also found in many rhynchodids which are mostly parasites of

bivalve Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...

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Further reading