Phylogenetic analysis of a fish tapeworm, Proteocephalus exiguus, based on the small subunit rRNA gene

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Within Platyhelminthes, phylogenetic trees based on the total small subunit ribosomal RNA gene (SSU rRNA) sequences have been constructed only for the aspidogastrean Lobatostoma manteri, the monogenean Gyrodactylus salaris and some digenetic trematodes, mainly schistosomes [1–5]. Besides these data, partial sequences of SSU rRNA genes of some other helminths have been described. However, no complete sequences of the rRNA gene of any cestode have been published and only that of the cyclophyllidean Echinococcus granulosus is available in the GenBankTM (Picon et al., unpublished results). Herein, the complete sequence of SSU rRNA of Proteocephalus exiguus La Rue, 1911 (Cestoda: Proteocephalidae) is presented and the phylogenetic position of this parasite is determined. The SSU rRNA sequence of P. exiguus was aligned with the other eukaryotic SSU rRNA sequences [6] using the DCSE sequence editor [7]. An evolutionary tree was constructed by the neighbor-joining method and bootstrap analysis, involving the computation of 500 trees from resampled data, was performed using the software package TREECON for Windows [8]. Maximum likelihood [9] and maximum parsimony [10] methods were used to construct alternative trees. The evolutionary trees based on the neighborjoining and maximum likelihood methods (Figs. 1 * Corresponding author. Tel.: +42 38 817, ext. 428; fax: +42 38 47743; e-mail: jula@paru.cas.cz 1 Note: Nucleotide sequence data reported in this paper will appear in the EMBL, GenBankTM and DDBJ Nucleotide Sequence Databases under the accession number X99976. 2 Permanent address: Institute of Parasitology, Slovak Academy of Sciences, Hlinkova 3, 040 01, Kos' ice, Slovakia.