European Journal of PROTISTOLOGY European Journal of Protistology 44 (2008) 254–262 Phylogeny of some systematically uncertain urostyloids – Apokeronopsis, Metaurostylopsis, Thigmokeronopsis (Ciliophora, Stichotrichia) estimated with small subunit rRNA gene sequence information: Discrepancies and agreements with morphological data Zhenzhen Yi a , Weibo Song a,Ã , Chen Shao a , Alan Warren b , Khaled A.S. Al-Rasheid c , David McL. Roberts b , Miao Miao a , Saleh A. Al-Quraishy c , Zigui Chen a a Laboratory of Protozoology, KLM, Ocean University of China, Qingdao 266003, China b Department of Zoology, the Natural History Museum, Cromwell Road, SW7 5BD, UK c Zoology Department, King Saud University, P. O. Box 2455, Riyadh 11451, Saudi Arabia Received 2 November 2007; received in revised form 19 December 2007; accepted 22 December 2007 Abstract The small subunit rRNA (SSrRNA) genes of seven species of urostyloids representing four genera were sequenced. These were: Apokeronopsis crassa, A. bergeri, Anteholosticha sp-QD-1, Metaurostylopsis sp-QD-1, M. sp-QD-2, M. sp- QD-3 and Thigmokeronopsis sp-QD-1. Gene trees were constructed in order to investigate their phylogenetic relationships. The results indicate that: (1) Apokeronopsis, Thigmokeronopsis and Metaurostylopsis form a well- supported, clearly isolated, monophyletic group; (2) Metaurostylopsis species analysed consistently group together indicating that it is a well-outlined genus; (3) the validity of the genus Apokeronopsis is supported; (4) the separation of Holosticha and Anteholosticha is supported although Anteholosticha species exhibit a high molecular diversity; (5) Pseudokeronopsis and Thigmokeronopsis, which have been considered closely related, may not share a recent common ancestor, casting doubt on the monophyly of the family Pseudokeronopsidae. r 2008 Elsevier GmbH. All rights reserved. Keywords: Urostylids; Urostyloidea; Hypotrichs; Ciliates; Taxonomy; Phylogeny Introduction The urostyloids are mainly defined by the possession of a zig-zag pattern of midventral cirri which differ- entiates during division from a longitudinal field of oblique FVT-streaks (Borror 1979; Borror and Wicklow 1983). Several different classification schemes of the urostyloids based on morphological data have been suggested (e.g. Berger 2006; Borror 1972, 1979; Corliss 1979; Lynn and Small 2002), of which that proposed by Berger (2006) is the most detailed. He included 154 valid species within the urostyloids, and assigned most species to four groups (Holostichidae, Bakuellidae, Urostylidae and Epiclintidae) using the frontal ciliature and the midventral complex as the main features. Small subunit rRNA (SSrRNA) gene sequences of at least 20 species are available in the GenBank database, but analyses based on morphological vs. molecular data have usually resulted in conflicting conclusions in terms of the placement of the Urostyloidea (Foissner et al. 2004). Combining the morphological and molecular data, ARTICLE IN PRESS www.elsevier.de/ejop 0932-4739/$ - see front matter r 2008 Elsevier GmbH. All rights reserved. doi:10.1016/j.ejop.2007.12.002 Ã Corresponding author. Tel.: +86 532 8203 2283. E-mail address: wsong@ouc.edu.cn (W. Song).