Structural and ultrastructural observations of the ciliate Phacodinium metchnicoffi certes, 1891 (Heterotrichea, Phacodiniida)

Abstract

This work points out several specific ultrastructural characteristics of the ciliate Phacodinium metchnicoffi. The somatic infraciliature consists of several segments of aciliferous or partially ciliferous monokinetids or alignments of kinetosomes with a particular structuration. All alignments of kinetosomes in double rows are associated with striated kinetodesmal fibers and to a ribbon of postciliary microtubules. The transverse fibers are observed only from monokinetids showing also kinetosomes associated with a 1-2 ribbon of transverse microtubules. However, only the anterior kinetosome of the monokinetid presents a ribbon of transverse fibers and an isolated microtubule next to triplet 5. The somatic kinetosomes located in the zones surrounding the buccal area are clearly associated with a noded microfibrillar network and with nemadesmata on the remaining part of the cortex. The kinetosomes of adorai organelles show 1-2 transverse microtubules. Each organelle is provided with 4 rows of kinetosomes and on each organelle, the kinetosomes of the anterior row bear postciliary microtubules directed towards the front part of the membranelle. The kinetosomes of the left row are associated with 1 or 2 transverse microtubules (T2) as are the kinetosomes of the other rows. The paroral organelle consists of an internal row of kinetosomes accompanied by a succession of parallel small rows each consisting most often of 3 kinetosomes. Only the kinetosomes of the internal row bear postciliary microtubules and prepostciliary microtubules and also show a noded microfibrillar network connecting their proximal zones. Lastly, the taxonomic relationships between Transitella and Phacodinium are discussed.