Phylogenetic relationships of freshwater bryozoans (Ectoprocta, Phylactolaemata) inferred from mitochondrial ribosomal DNA sequences

Authors

  • Makiko Okuyama,

  • Hiroshi Wada,

  • Teruhisa Ishii


Makiko Okuyama, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan. E-mail: m_okyma@yahoo.co.jp

Hiroshi Wada, University of Tsukuba, Tsukuba, Ibaraki 305–8572, Japan. E-mail: hwada@biol.tsukuba.ac.jp

Teruhisa Ishii, Division of Biology, Department of Natural and Environmental Sciences, Akita University, Akita 010-8502, Japan. E-mail: tishii@ipc.akita-u.ac.jp

Abstract

Most species of freshwater bryozoans (Ectoprocta: Phylactolaemata) have few morphological distinctions, and within phylactolaemates, the morphology of the statoblast has been used to determine evolutionary relationships. Here, two controversial phylogenies have been proposed for phylactolaemates with regard to the relationship of Lophopodidae to other families. Two plumatellid genera, Gelatinella and Hyalinella, are candidates for the ancestral type of lophopodids. In addition, the coexistence of spines on the surfaces of the statoblast has led to the suggestion that lophopodids are closely related to the family Cristatellidae. In this study, we analysed mitochondrial DNA sequences of the 12S and 16S rDNA genes of 10 phylactolaemate species. Our results suggest that plumatellids may not be a direct ancestral group of lophopodids and that cristatellids are not a sister group of lophopodids. Fredericella, which was previously thought to be an ancestral group, was revealed to be derived. In addition, our results suggest that Stephanella is the most basal phylactolaemate. Mapping morphological characteristics onto the sequence-based phylogenetic tree revealed convergent evolution of statoblast characters.

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