Phylogenetic relationships of Spiruromorpha from birds of prey based on 18S rDNA M. Honisch* and O. Krone Leibniz Institute for Zoo and Wildlife Research, PO Box 601103, Berlin D-10252, Germany Abstract A total of 153 free-ranging birds from Germany belonging to 15 species were examined for nematodes in their digestive and respiratory tracts. In 51.7% of the birds 14 different nematode species were found: the intestinal ascarids Porrocaecum depressum and P. angusticolle, the strongylid Hovorkonema variegatum, which inhabits the trachea and bronchi, the hairworms Eucoleus dispar and Capillaria tenuissima isolated from the digestive system, the spirurid nematodes Cyrnea leptoptera, C. mansioni, C. seurati, Microtetrameres cloacitectus, Physaloptera alata, P. apivori, Synhimantus hamatus and S. laticeps, which inhabit the proventriculus and gizzard of the raptors, and the spirurid nematode Serratospiculum tendo, which lives in the air sacs. To revise their systematic positions the ribosomal 18S gene regions of the nematode species were analysed and a phylogenetic tree was constructed. The molecular data confirmed the morphological systematics, except the spirurid family Physalopteridae, which grouped together with the Acuariidae. Introduction Historically, the systematics of nematodes were based on host specificity, life cycle and morphological features such as the digestive tract, mouth capsule or reproductive organs (Durette-Desset et al., 1994). The difficult structure of morphological traits, together with a high level of homoplasy and a lack of information about life traits of many species, led to problems in determining phyloge- netic relationships of nematodes (Chilton et al., 1997). Moreover, phylogenetic reconstructions were hindered by the extremely high number of species of these ecologically diverse helminths (Dorris et al., 1999). In general, the morphological identification of closely related nematodes species is difficult (Blaxter, 2003). For this reason molecular techniques were introduced in addition to morphological traits for species identification independent of developmental stages (Gasser, 2001). In recent years ribosomal DNA has been used most extensively for investigating phylogenetic relationships of nematode species (Blouin, 2002). Besides the highly variable, non-coding internal transcribed spacer regions (ITS-1, ITS-2), which are commonly used to distinguish between closely related species (Gasser & Newton, 2000) or for detecting cryptic species (Chilton et al., 1995), the slowly evolving 18S (small subunit, SSU) gene region is a useful tool for the analysis of distantly related taxa (Meldal et al., 2007). The results of the molecular analyses led to a fundamental revision of nematode phylogeny. Since Blaxter et al. (1998) analysed the phylogenetic relation- ships of 53 nematode species based on 53 SSU sequences, actually more than 300 SSU sequences of nematode taxa, including parasitic and free-living nematode species, are now known (Blaxter, 2003). The main focus of most studies was on investigating economically or medically important species, primarily of humans or domestic animals (Lukes et al., 2005). Hence some areas of nematode phylogeny are still underrepresented, especially the species-rich infraorder Spiruromorpha, which includes a heterogeneous group of, mainly parasitic, nematodes. The former order Spirurida has been reclassified several times recently. The division in the suborder Camallanina, which was divided in two superfamilies, and the suborder Spirurina, which was divided into ten superfamilies (Anderson & Bain, 1975, *E-mail: honisch@izw-berlin.de Journal of Helminthology (2008) 82, 129–133 doi: 10.1017/S0022149X08912359