Cell-division pattern and phylogenetic position of a new ciliate genus Parasincirra n. g. (Protista, Ciliophora, Hypotrichia), with report of a new soil species, P. sinica n. sp. found from northwest China

Abstract

Ciliated species, unicellular eukaryotes, are extremely diverse and occupy a very broad spectrum of ecological niches. Even though there is a growing recognition that enormous ciliates associates with key ecosystem processes in different niches, their diversity is not well understood. One reason is that ciliates are very tiny and may often be overlooked in routine biodiversity survey. Furthermore, the morphological and genetic diversity of ciliates per se is vast and dwarfs that among other multicellular eukaryotes. Here, we present the study of a new stichotrichid ciliate, Parasincirra sinica n. g., n. sp. based on classical living morphology, infraciliature, ontogenesis analyses and a comprehensive phylogenetic study, and enhance understanding of ciliates diversity in sludge soil. This new, monotypic genus is defined by having a bipartite adoral zone of membranelles, three frontal cirri, an amphisiellid median cirral row about as long as, or slightly longer than, the adoral zone, one short frontoventral cirral row, cirrus III/2 and transverse cirri present, buccal cirrus and caudal cirri absent, three dorsal kineties. The main morphogenetic features are: (1) five frontoventral-transverse cirral anlagen (excluding undulating membranes anlage) are formed in primary mode; (2) the amphisiellid median cirral row is formed by anlagen V and VI, while the frontoventral row is generated from anlage IV; (3) cirral streaks IV to VI generate one transverse cirrus each; (4) frontoventral-transverse cirral anlage II generates one or two cirri, while the posterior one will be absorbed in late stages, that is, no buccal cirrus is formed; (5) the posterior part of the parental adoral zone of membranelles is renewed; (6) dorsal morphogenesis follows a typical Gonostomum -pattern. Based on the SSU rDNA information, analyses of the phylogenetic relationship inferred from Bayesian inference and maximum likelihood analyses were unable to outline the exact position of this new form among some other species of related genera which are generally assigned in the family Amphisiellida . The morphological/ morphogenetical differences between the new genus/species and Uroleptoides / Parabistichella , as well as other amphisiellids, clearly support the validity of the establishment of this new genus Parasincirra .