Observations on temnocephalid (Platyhelminthes) ectosymbionts in Australian freshwater crayfish (Cherax destructor Clark) introduced into northern Italy

In 1996, freshwater crayfish (Cherax destructor Clark, 1936) were imported to Italy from Australia in order to explore their potential for aquaculture. Ten dead and moribund specimens were examined after arrival at our laboratory and 10 live specimens were kept in a tank during the period from June to December. Temnocephalid platyhelminths were detected on the external surfaces (exoskeleton and gills) of all crayfish. Strongly adherent temnocephalid eggs were also found on the cuticle and gills. Morphological features of the temnocephalid worms were examined by electron microscopy. General morphology, number of tentacles and size of the sucker indicated that the examined specimens were Temnocephala minor Hanswell, 1887. Other crayfish such as Austropotamobius pallipes (Lereboullet, 1858), Orconectes limosus (Rafinesque, 1817) and Procambarus clarkii(Girard, 1852), were infested by the worms when placed in the same tank. The health of all observed crayfish species, whether Australian, American or European, was not visibly affected by the infestation. The effect of these parasites on the well-being of European host species is unknown.