Hypotrichidium tisiae(Gelei,1929)Gelei,1954:a unique hypotrichid ciliate having a highly specialized developmental pattern during binary division

In sharp contrast to their pelagic relatives,the oligotrichs,the overwhelming majority of hypotrich ciliates inhabit the benthos.Only a few species,including those of the genus Hypotrichidium Ilowaisky,1921,have adapted to a planktonic lifestyle.The ontogenetic mode of the highly differentiated ciliate,Hypotrichidium tisiae(Gelei,1929)Gelei,1954,is unknown.In this study,the interphase morphology and the ontogenetic process of this species are investigated.Accordingly,the previously unidentified ciliary pattern of Hypotrichidium is redefined.The main morphogenetic features are as follows:(1)The parental adoral zone of membranelles is inherited completely by the proter and the oral primordium of the opisthe arises in a deep pouch.(2)Five frontoventral cirral anlagen(FVA)are formed:FVA I contributes to the single frontal cirrus,FVA II–IV generate three frontoventral cirral rows,FVA V migrates and forms postoral ventral cirri.(3)All marginal cirral row anlagen develop de novo:each of the two left anlagen forms a single cirral row,while the single right anlage fragments into anterior and posterior parts.(4)Two dorsal kinety anlagen occur de novo,with the right one fragmenting to form kineties 2 and 3.(5)Two long caudal cirral rows are formed at the ends of dorsal kineties 1 and 3.On the basis of the morphogenetic features and phylogenetic analyses,the assignment of Hypotrichidium to the family Spirofilidae Gelei,1929 within Postoralida is supported.The establishment of separate families for the slender“tubicolous”spirofilids and the highly helical spirofilids is also validated.

A new contribution to the taxonomy and phylogeny of the ciliate genus Spirostomum(Alveolata,Ciliophora,Heterotrichea),with comprehensive descriptions of two species from wetlands in China

Species of the ciliate genus Spirostomum Ehrenberg,1834 are distributed worldwide and have a research history spanning more than two centuries.However,species delimitation and phylogenetic relationships within this genus are still uncertain due to the paucity of stable morphologic characters for species separation and the unavailability of accompanying morphological data for most molecular sequences in public databases.In the present study,S.yagiui Shigenaka,1959(three populations)and S.caudatum(Müller,1786)Delphy,1939(one population)were investigated using morphological and molecular methods for the first time in China.Detailed morphological data for the two species were documented,and improved diagnoses were supplied based on a combination of previous studies and the current work.It should be highlighted that there were three different atypical morphotypes identified in a Ningbo population of S.yagiui which may represent various stages in conjugative reproduction.Molecular phylogenies based on 18S,ITS1-5.8S-ITS2,and 28S rRNA gene sequences show that the genus Spirostomum is monophyletic,however,the internal relationships inferred from different genes were poorly resolved but suggest that the species with a moniliform macronucleus comprise an early-diverging clade within this genus.Finally,the global distribution of Spirostomum is summarized based on previous and present studies.