Morphology, morphogenesis and phylogeny of the new soil ciliate, Bistichella granulifera n. sp. (Protista, Ciliophora)

Abstract

Background: Hypotrichous ciliates are showing extremely morphological diverse and complicated morphogenesis. However, many hypotrichs are still unknown/poorly-known and need to be explored. Recently, Foissner (2016) reassigned the species in Bistichella and Parabistichella. Due to lack of morphological and morphogenetic information, some problems were overlooked. In present work, a new species, Bistichella granulifera n. sp., was found in northern China. Based on its infraciliature, ontogenesis analyses and phylogenetic study, the phylogenetic position of Bistichella was discussed.Results: Bistichella granulifera n. sp. was characterized by having elongated oval body, two macronuclear nodules, cortical granules present, three frontal and three or four buccal cirri, three frontal rows with seven to ten cirri, usually two frontoventral rows with the left one usually terminates at 90% down length of body and no breaks in the right one. The main morphogenetic features of the novel species were as follows: (1) the posterior part of the old adoral membranelles is renewed; (2) frontoventral-transverse cirral anlagen III to V each form a frontal row, and anlagen VI to n each produce a frontoventral row; (3) both marginal rows and dorsal kineties develop intrakinetally; (4) the macronuclear nodules fuse to form a single mass. The gene sequence of Bistichella was investigated for the first time. Phylogenetic analyses based on the SSU rDNA sequences showed that the Bistichella groups with the non-dorsomarginalian hypotrichs.Conclusions: Morphology, morphogenesis and phylogenetic position of Bistichella granulifera n. sp., was investigated. Each frontoventral row originates from one anlage and only three bipolar dorsal kineties are present in the new species, which means it should belong to non-Dorsomarginalia rather than Amphisiellidae. Even though Bistichella has a close relationship with amphisiellids, due to the limited gene sequence, the phylogenetic position of Bistichella needs more data to be fully understood.