Morphological and molecular analyses of the spiruroid nematode, Falcaustra araxiana Massino, 1924 (= Spironoura araxiana) from the European pond turtle (Emys orbicularis)

There is little information on the phylogenetic position and life cycle of family Kathlaniidae. Falcaustra araxiana is a member of this family which infects the large intestine of the European pond turtle (Emys orbicularis). In the present study, morphological data and molecular analyses based on the 18S rDNA were performed on different types of F. araxiana originating from the large intestine and gastric nodules in the turtle. Morphological data revealed both larvae and adult stages in the gastric nodules. In addition, all nematodes recovered in the large intestine were adult worms. GenBank accession numbers KM200715 and KM200716 were provided for adult F. araxiana located in the intestine and stomach, respectively, of E. orbicularis. The results of sequencing proved that these two types are completely similar. Accordingly, it can be hypothesized that nodule formation is a part of the life cycle of the parasite or a survival strategy. Furthermore, F. araxiana develops to the adult stage in the gastric mucosa prior to migrating to the large intestine. Phylogenetic analysis revealed that F. araxiana unexpectedly branched away from other members of the superfamily Seuratoidea (Truttaedacnitis truttae, Cucullanus robustus and C. baylisi) and showed a closer relationship with Paraquimperia africana, a member of the Ascaridoidea. It seems that phylogenetic reconstruction for the present parasite needs more detailed morphology, life cycle and molecular studies.