Presence and Histopathological Effects of the Copepod Pseudomyicola spinosus in Mytilus galloprovincialis and Mytilus californianus.

The copepod Pseudomyicola spinosus (Cyclopoidea, Myicolidae) was found in the mantle, gills, intestine, stomach, and connective tissue of the digestive gland of the blue mussel Mytilus galloprovincialis and the California mussel Mytilus californianus from Baja California, northwestern Mexico. The copepod can move from the mantle and gills to the digestive gland and vice versa. In M. galloprovincialis, copepod prevalence was 93% and its number ranged from 0 to 20 (mean, 5) in the mantle and gills and from 0 to 5 (mean, 1.1) in the digestive gland. In M. californianus, copepod prevalence was 43% and its number ranged from 0 to 2 (mean, 0.4) in the mantle and gills and from 0 to 1 (mean, 0.1) in the digestive gland. In the epithelium of the stomach and intestine of both mussel species studied, the appendages of P. spinosus may produce a loss of epithelial cells. Occasionally there was a light increase of hemocytes at the basal region of the stomach and intestinal epithelia where copepod was attached. In the lumen of the stomach and intestine copepods may be surrounded by mucus. P. spinosus was also found among the connective tissue of the digestive gland, apparently as a result of penetration through the wall of the stomach or other digestive organs. A granuloma-like structure engulfing the copepod in the connective tissue of the digestive gland was found. This is the first description of histopathological effects of P. spinosus in mussels.