Abstract
Redclaw crayfish (Cherax quadricarinatus) is a decapod species originating from Australian freshwater. For more than two decades, these crayfish have been re-distributing to environments in many countries, including Thailand. Moreover, they can carry endosymbionts and/or ectosymbionts into new environments. The aim of this study was to introduce a morphological description of Pseudolevinseniella anenteron as a metacercaria of the endoparasites of redclaw crayfish collected from natural water sources in Thailand. The occurrence of two ectosymbiotic temnocephalans (Diceratocephala boschmai and Temnosewellia sp.) in C. quadricarinatus was also reported. The internal morphology of P. anenteron, D. boschmai and Temnosewellia were described and discussed. The surface ultrastructure of the multidentate spines on the body and the metacercarial cyst wall of P. anenteron was investigated by scanning electron microscopy (SEM). By performing a search of the GenBank nucleotide database of partial sequences of 18S, 28S rDNA and cytochrome c oxidase subunit I (cox1), P. anenteron was found to be related to Maritrema, and Temnosewellia was found to be related to T. fasciata. However, according to the cox1 gene, Temnosewellia was found to be similar to T. minor. These results reveal that redclaw crayfish that inhabit natural freshwaters in Thailand may harbour endoparasites and ecto- and endosymbionts. Furthermore, these findings may be able to monitor invasive or non-invasive species in an ecosystem.