The facultatively parasitic ciliated protozoan, Tetrahymena glochidiophila (Lynn, 2018), causes a reduction in viability of freshwater mussel glochidia.

This study investigated the effect of a previously uncharacterized species of ciliated protozoan, Tetrahymena glochidiophila, on the viability of glochidia from three species of freshwater mussel (Lampsilis siliquoidea, Lampsilis fasciola, and Lampsilis cardium). Over the course of 72 h, the viability of glochidia exposed to T. glochidiophila declined by >60% while the decline in the viability of uninfected glochidia was <10%. The density of T. glochidiophila increased >1000-fold during the experiment in treatments with infected glochidia. Lampsilis cardium glochidia were also either exposed to gill rinsate or gill contents from infected gravid female L. siliquoidea for the purpose of elucidating the location of the greatest density of ciliates within infected mussels. Glochidia exposed to gill contents declined significantly (p < 0.05) more than glochidia exposed to gill rinsate. Finally, a clone of ciliates was isolated from infected glochidia and cultured on bacterized medium. The clonal culture was then used to expose uninfected glochidia for the purpose of further confirming a parasitic relationship between glochidia and T. glochidiophila. The viability of glochidia exposed to T. glochidiophila from the clonal culture declined significantly relative to uninfected glochidia but not to the extent of glochidia exposed to ciliates from the gills of infected L. siliquoidea.