First Record of . Looss, 1899 (Digenea: Acanthocolpidae) Metacercariae Parasitising the Pleasure Oyster (Hertlein) from the Mexican Pacific Coast.

The aim of this investigation was to identify the parasites present in the largely understudied pleasure oyster in Sinaloa state in the northwestern Mexican Pacific coast. Inspection of twenty-eight oysters collected on "Ceuta" lagoon revealed the presence of the digenean . (Digenea: Acanthocolpidae) cysts. Metacercariae were found encapsulated and embedded in the digestive gland and mantle tissue of oysters. The prevalence of infection revealed that 84.6 % were infected, the abundance was 13.62, with a mean intensity of 16.09 per host. The members of this genus are characterized by a double crown of spines in the cephalic region surrounding the buccal opening of the worm. Significantly, we report the first incidence of the digenean sp of the family Acanthocolpidae parasitizing . Further we report that this bivalve is now considered a new intermediate host, and the northwestern Mexican Pacific coast is a new geographical distribution area for this digenean. The findings contribute to our understanding of the biology, biodiversity and host preference of these parasites, with implications for health risks posed by human consumption of the pleasure oyster.