The marine mites Hyadesia sp. and Copidognathus sp. Associated with the mussel Mytilus galloprovincialis.

Two species of marine mites belonging to the families Hyadesiidae and Halacaridae, Hyadesia sp. and Copidognathus sp., respectively, were found associated with the mussel Mytilus galloprovincialis from Baja California in NW México. The first species was found inside the mussel gut with an intensity ranging from one to six mites per mussel and their prevalence was from 20.0 to 46.7%; this species was also found living free in the sediment at a density of 0.7 mite/100 ml. The second species was found on the mantle and gills of the host with an intensity ranging from one to three mites per host and their prevalence was from 3.3 to 6.7%; this species was abundant (4.5 mites/100 ml) and living free in the sediment around mussel clumps. Hyadesia sp. was found alive and attached in the gut of the mussel. A histological analysis revealed this species in the lumen of intestine surrounded by mucus and attached to the epithelial cells of the intestine, where some disorder of epithelial cells was associated. Moreover, this mite may be encapsulated by hemocytes inside the digestive diverticulum, the reproductive follicle, or the connective tissue surrounding the diverticulum. No damages to branches or gills resulting from the presence of Copidognathus sp. were observed. The results suggest that these mites are occasional invaders of mussels; however, as a result of this infestation, Hyadesia sp. may produce damage in the host's tissues. This is the first record of marine mites inside the gut, reproductive follicles, branches, and mantle of a marine bivalve.