MOLECULAR PHYLOGENETICS OF P. PSEUDOHETEROTREMUS Vol 39 No. 2 March 2008 217 Correspondence: Jitra Waikagul, Department of Helminthology, Faculty of Tropical Medicine, 420/6 Ratchawithi Road, Bangkok 10400, Thailand. E-mail: tmjwk@mahidol.ac.th INTRODUCTION The genus Paragonimus Braun, 1899 contains more than 40 species, which are di- vided into two main groups. One group con- sists of P. westermani and P. siamensis and the other all the remaining species from Asia and America (Blair et al, 1998). The latter group shows P. skrjabini and P. macrorchis are well separated (Blair et al, 1999). P. skrjabini is very closely related to P. miyazakii from Japan (Blair et al, 1997) and this relationship is called P. skrjabini complex (Blair et al , 2005). P. hokuoensis was proposed as a sister species to P. skrjabini complex. The P. ohirai group consists of P. iloktsuenensis and P. sadoensis. P. harinasutai is closely related to P. ohirai (Blair et al, 1998). Although Euparagonimus ceno- copiosus has been recognized as a distinct taxon, it seems that this species should not be placed in a distinct genus as E. ceno- copiosus is nested among species assigned to the genus Paragonimus and Pagumogo- nimus (Blair et al, 1999). Recently, a new species of Paragonimus similar to Paragonimus heterotremus has been described as Paragonimus pseudohetero- tremus (Waikagul, 2007). The adult worm is similar to P. heterotremus in morphology of the ovary and testes, and in the ratio of suckers and spination. However, it is distinctly differ- ent to P. heterotremus in the sizes of meta- cercariae and adults in the definitive hosts. P. pseudoheterotremus metacercaria is smaller in size and has a thicker cyst wall. The adult is smaller but the integument spines are big- ger. The rat is considered a definitive host, while P. heterotremus is unable to become fully mature in the rat (Waikagul, 2007). In this pa- per, partial cytochrome c oxidase subunit I (COI) gene and the nuclear ribosomal DNA second internal transcribed spacer 2 (ITS2) DNA sequences of P. pseudoheterotremus were analyzed and compared with P. heterotremus to determine the phylogenetic position of P. pseudoheterotremus within the genus Paragonimus. RESEARCH NOTE MOLECULAR PHYLOGENETIC RELATIONSHIP OF PARAGONIMUS PSEUDOHETEROTREMUS Urusa Thaenkham and Jitra Waikagul Department of Helminthology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand Abstract. A part of the mitochondrial cytochrome c oxidase subunit I (COI) gene and the nuclear ribosomal DNA second internal transcribed spacer 2 (ITS2) of a newly described lung fluke, Paragonimus pseudoheterotremus, were sequenced and compared with P. heterotremus, the species with a similar morphology. Pairwise distance of COI sequences revealed a genetic difference between P. heterotremus and P. pseudoheterotremus with a nucleotide difference of COI sequences between these two species of 10.6%. The constructed phylogenic tree with high bootstrap proportion suggested that P. pseudoheterotremus is a sister species of P. heterotremus.