THE TURBELLARIAN URASTOMA-CYPRINAE FROM EDIBLE MUSSELS MYTILUS-GALLOPROVINCIALIS AND MYTILUS-CALIFORNIANUS IN BAJA-CALIFORNIA, NW MEXICO

The turbellarian Urastoma cyprinae (Graff, 1913) was found in the mant le cavity of Mytilus galloprovincialis Lamarck and Mytilus californian us Conrad, on the Pacific coast of Baja California NW Mexico. This is the first record of this turbellarian for bivalves from the Pacific co ast of North America. In M. galloprovincialis from an exposed rocky sh ore, prevalence ranged from 10 to 87% and mean number of turbellarians per infested mussel was 1.9; in a culture area prevalence ranged from 57 to 100% and the mean number of turbellarians per infested mussel w as 7.4. In the protected and polluted areas U. cyprinae was scarce or absent, prevalence ranging from 0 to 15% and the mean number of turbel larian per infested mussel being 0.07. The prevalence and the mean num ber of turbellarians per M. californianus in the exposed rocky shore f rom 20 to 100% and 5.1, respectively. There were more worms in the lar ger mussels. Demibranches of M. galloprovincialis and M. californianus may be injured by the presence of turbellarians. An infiltration of h emocyte cells around the turbellarians was observed in both species an d the blood sinuses in the infected area were engorged. Recorded damag e was not related to a negative effect on the condition index of musse ls. (C) 1998 Academic Press.