MORPHOGENETIC AND ULTRASTRUCTURAL INVESTIGATION IN THE HYPOTRICHIDA (CILIOPHORA, PROTOZOA): IMPLICATIONS IN CILIATE EVOLUTION
Hypotrichs represent a highly diverse species ensemble displaying a wide range of form and function that reflects extensive radiation in a wide variety of habitats. Because of their constancy through time, particular habitats such as marine sands harbor forms that may have persisted with little change for hundreds of millions of years and, hence, may hold clues to help unravel mysteries of ciliate evolution. Using light optical microscopy and both scanning and transmission electron microscopy, I examine cortical morphogenesis through cell division and interphase ultrastructure of several species of marine ciliates. Using this information I propose phylogenetic relationships within the Hypotrichida, suggest homologies between hypotrichs and other ciliates, discuss the adaptive significance of ciliate microtubular organelles, and explore the evolution of cellular complexity in general. I described morphogenesis, ultrastructure, and polymorphism in Discocephalus ehrenbergi as well as structure and morphogenesis in Psammocephalus borrori (n.gen., n.sp.), Psammocephalus faurei (n.comb.), and Amphisiella marioni. D. ehrenbergi is ultrastructurally and developmentally divergent from that of other hypotrichs. Psammocephalus is structurally and developmentally similar to Discocephalus but different from Amphisiella and serves as an intermediate in an evolutionary series that demonstrates a trend in the Discocephalina (n.subord.) toward increased cytoskeletal complexity, cirral reduction and hypertrophy, and ovoid cell shape. In Certesia, postciliary microtubules from membranellar kinetosomes line the buccal cavity and separate parallel arrays of pharyngeal discs; alveolar plates and lasiosomes are present. During morphogenesis microtubular bundles appear beside (later attached to) developing frontal anlagen. These microtubules may be involved in mediating placement of cortical structures during morphogenesis. The morphogenetic pattern of Thigmokeronopsis jahodai (n.gen.,n.sp.) is of the Urostyline type, while ultrastructural and developmental specializations of Epiclintes justify erection of the Epiclintina (n.subord.).
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