Subphylum 2. INTRAMACRONUCLEATA: Class 3. LITOSTOMATEA – Simple Ciliates but Highly Derived

Abstract

The ciliates in this class are divided into two major assemblages, represented by the Subclass Haptoria and Subclass Trichostomatia. The haptorians are predatory ciliates that are commonly found in a variety of habitats, feeding on flagellates and other ciliates, which they immobilize and kill with extrusomes called toxicysts. An exception to this rule is the marine planktonic haptorian Myrionecta rubra, which harbors a cryptophyte endosymbiont and which produce red tides that contribute up to 70% of the primary production. The trichostomes have lost toxicysts and are all endosymbionts in a variety of metazoans, ranging from fish to humans. In fact, the only ciliate known to be pathogenic to humankind is the trichostome Balantidium, which can be an intestinal parasite. The somatic monokinetid of litostomes is unique in possessing two transverse microtubular ribbons, T1 and T2 - a strong synapomorphy for the class. Oral structures are typically simple, hence the name litos (Gr.) for simple. Haptorians typically have either circumoral dikinetids or oralized monokinetids. Trichostomes show more diversity: some forms, like Balantidium, have a vestibulum with extensions of densely packed somatic kineties lining it, while the entodiniomorphids have polybrachykineties, more complex assemblages of short kinetofragments. Stomatogenesis is characterized as telokinetal, but there is a range of types from holotelokinetal to cryptotelokinetal