First record of the nematode Echinocephalus pseudouncinatus (Gnathostomatidae, Spirurida) in an edible, commercial host, the pen shell Atrina maura (Bivalvia: Pinnidae).

We describe a nematode infestation of the Atrina maura, the most valuable pen shell fished in Mexico, for the first time. Observations by Mexican authorities indicated that parasites were found encysted in pen shell gonads. The aims of this study included: (i) to identify the parasite morphologically; (ii) to quantify the infestation in different tissues of the pen shell; and (iii) to establish the seasonal variation in gonadal development.