Pseudomyicola spinosus is a parasitic copepod that is found in more than 50 species of bivalves around the world, ranging from clams to mussels to scallops. It dwells in the mantle cavity of the bivalve, where it grazes on mucus produced by the host. This copepod has a pair of hook-like attachment appendages that allow it to cling to the host tissue and avoid being swept away by the constant water flow that passes through the mantle cavity. In large numbers, they can cause considerable tissue damage to the host - the constant attachment and reattachment of the copepod (which can be highly mobile within the host's body cavity) aggravate host tissue, causing epithelial erosion and induce over-production of mucus. At lower infection levels, the tissue damage caused by the copepod is almost negligible, but it does have a more subtle effect on its host. It has been found that infection with just a few P. spinosus is associated with higher levels of infections by metcercarial cysts of echinostomatid trematodes such as Curtuteria australis and Acanthoparyphium. Once again, this is possibly due to the effects of the copepod's attachment appendages, which damage the epidermis in such a way that facilitates subsequent invasion by trematode cercariae.
Cáceres-Martínez, J. and Vásquez-Yeomans, R. (1997). Presence and histopathological effects of the copepod Pseudomyicola spinosus in Mytilus galloprovincialis and Mytilus californianus. Journal of Invertebrate Pathology 70, 150–155.
Leung, T. L. F. and Poulin, R. (2007). Interactions between parasites of the cockle Austrovenus stutchburyi: Hitch-hikers, resident-cleaners, and habitat-facilitators. Parasitology 134, 247–255.
Post and image by Tommy Leung.