Based on a near-complete mitochondrial DNA sequence, the phylogenetic status of a lung fluke collected in the Philippines was evaluated. The lung fluke from Leyte Island, Philippines, resembles Paragonimus westermani morphologically and is sometimes regarded as a subspecies, P westermani filipinus. In this study, all mitochondrial genes of the Leyte form were sequenced : 12 subunits of mitochondrial enzymes, 2 ribosomal RNA genes and 21 transfer RNAs. The gene order is the same as that of the previously-published P. westermani from Korea. All genes are transcribed in the same direction. The sequence from Leyte was 88.8% identical to the previously-published sequence (accession No. AF219379). This is further evidence that the Philippine form should be regarded as specifically distinct from the form in East Asia (China, Japan and Korea). This conclusion is strengthened by the observation that the molluscan host of the Philippine form is of a different family from that of the East Asian form.

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The Schistosoma japonicum group and S. sinensium utilize intermediate snail hosts belonging to the genera Oncomelania and Tricula (Gastropoda : Pomatiopsidae). In the present study, partial sequences of the mitochondrial 12S rRNA gene from 7 subspecies of O. hupensis, two species of Tricula (T bollingi and T humida) and O. minima were examined to infer a phylogeny for these. Nucleotide differences among subspecies of O. hupensis were less than 6.5% and among species from different genera, 10-12%. The phylogenetic tree obtained in this study indicates that O. hupensis subspecies fell into four distinct clades ; thatis, O. h. quadrasi from the Philippines, O. h. lindoensis from Indonesia, O. h. hupensis from Yunnan, China and the remaining 5 subspecies (O. h. hupensis from other parts of China, O. h. robertsoni from China, O. h. formosana from Taiwan, O. h. chiui from Taiwan and O. h. nosophora from Japan). The phylogenetic tree also showed that O. minima was placed as sister to all of the subspecies of O. hupensis. Possible evolutionary relationships amongthe snail hosts were discussed.

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