Parasite and symbiont fauna of Japanese littlenecks, Tapes philippinarum (Adams and Reeve, 1850), in British Columbia.
No infectious diseases were detected in 994 accidentally introduced Japanese littlenecks (also known as Manila clams) (T. philippinarum) from 21 localities in British Columbia, Canada. However, parasites or symbionts consisting of intracellular bacteria, protozoa, and metazoa were observed. Some of these organisms were thought to be enzootic to the Manila clams. These were: intracellular bacteria in the cytoplasm of the epithelial cells of the gills (at 10 localities, mean prevalence of 11.8%) and the digestive gland tubules (at 20 localities, mean prevalence 27.7%); Trichodina sp. along the surface of the siphons and mantle (at 18 localities, mean prevalence 46.3%); Rhynchodida ciliates attached to the gills (at 14 localities, mean prevalence 9.6%); Rhabdocoela turbellaria in the gut lumen (at 19 localities, mean prevalence 24.7%); and parasitic copepods, Mytilicola orientalis in the gut lumen (at 9 localities, mean prevalence 3.9%) and Pseudomyicola ostreae attached to the gills (at 4 localities, mean prevalence 2.5%). The other organisms found in the Manila clams are thought to have strayed from other molluscan hosts native to British Columbia. These were: Nematopsis-like apicomplexan spores usually in the connective tissue of the gills (at all localities, mean prevalence 40.7%); 2 different apicomplexans associated with the gut, (1) a gregarine-like Apicomplexa (at one locality, 33% infected) and (2) a coccidia-like Apicomplexa (at one locality, 15% infected); metacercariae of several species including members of the family Echinostomatidae and Derogenes varicus (family Hemiuridae), and parasitic cysts apparently consisting of a successful host response surrounding a degenerating metacercaria, all in the connective tissue of the body (at 13 localities, mean prevalence 8.6%); and pea crabs (Pinnixa faba, Pinnixa littoralis, and Fabia subquadrata) in the mantle cavity (at 10 localities, mean prevalence 13.7%). It is thought that some of the unidentified species of Trichodina and Rhynchodida may also be native to North America and may therefore represent new invaders of the Manila clam.