Phylum CILIOPHORA – Conjugating, Ciliated Protists with Nuclear Dualism

Abstract

The ciliated protozoa are a distinct group of protists characterized by (1) the presence of cilia derived from kinetosomes with three fi brillar associates; (2) nuclear dimorphism; and (3) conjugation as a sexual process. They are exceedingly diverse in shape and size, and may have evolved over 2 billion years ago. The ciliate body form likely evolved from a fl agellate that proliferated kinetids near its oral apparatus, and these kinetids became fi rst the ciliate paroral, which itself replicated to provide somatic kineties and fi nally the adoral kinetids. Ciliates are now divided into two subphyla and 11 classes based on features of nuclear division and the pattern of fi brillar associates in their somatic kinetids. They are found in a diversity of microhabitats, with the majority of species likely cosmopolitan. However, endemism appears to be characteristic of perhaps as many as 30% of the species. Ciliates are important components of the microbial loop, often responsible for consuming the majority of primary production and bacterial production in certain habitats. Their development is complex since the kinetid patterns of the somatic and oral cortex are themselves complex. This complexity has made them useful models for developmental biologists while different taxa to each other. The life cycles of cili-ates are also complex and clearly separate sexual processes from asexual reproduction. Sexual process , conjugation, occurs in the context of a breeding strategy, ranging from an inbreeding one to an outbreeding one. A new macronucleus typically develops at each conjugation cycle through a complicated set of processes of DNA fragmentation, diminution, and replication. However, this process likely occurs at each cell cycle in karyorelictean ciliates whose macronuclei do not divide.