Subphylum 2. INTRAMACRONUCLEATA: Class 4. PHYLLOPHARYNGEA — Diverse in Form, Related in Structure

Abstract

Phyllopharyngeans are divided into four subclasses, only one of which is dominated by free-living forms. The Subclass Cyrtophoria includes common members of biofi lm communities, from sea ice in Antarctica to waste water treatment plants. The Chonotrichia, Rhynchodia, and Suctoria are typically found as symbionts: chonotrichs are sessile ectocommensals on the appendages of crustaceans; rhynchodians are ectoparasites on the gills of bivalves; and suctorians are epibionts on metazoans, from crustaceans to turtles. The cyrtophorians and chonotrichs have heteromerous macronuclei, which suggests that they might be united into a larger tax-on, and this is supported by small subunit rRNA gene sequences. The somatic kinetid is a monoki-netid with a distinctly shaped and laterally directed kinetodesmal fi bril, and is underlain by sub kinetal microtubules. The cytopharyngeal apparatus is lined by microtubular ribbons, called phyllae, from which the class derives its name. Cyrtophorians and chonotrichs feed on bacteria and small algae. Rhynchodians use a single sucker to ingest cytoplasm of host cells, while suctorians typically have multiple sucking tentacles to catch primarily other ciliates. Division in cyrtophorians is characterized as merotelokinetal, but in chonotrichs and suctori-ans is characterized by specialized forms of budding. The macronuclear DNA is apparently highly fragmented, and as in the spirotrichs, differentiates after the formation of polytene chromosomes.