Ophryoglena hemophaga n. sp. (Ciliophora: Ophryoglenidae): A parasite of the digestive gland of zebra mussels Dreissena polymorpha

Abstract

Ophryoglena hemophaga n. sp. is described from a freshwater Dreissena polymorpha population in the Rhine delta of the Netherlands. This is the first ophryoglenine species (order Hymenostomatida, suborder Ophryoglenina) recorded as a molluscan parasite. As is typical of ciliates in the suborder Ophryoglenina, O. hemophaga exhibits a polymorphic life history with cystment and reproduction by palintomy. Trophonts were observed within digestive gland lumina, and zebra mussel hemocytes were present in some of their digestive vacuoles. The presence of a single, longitudinal tract of multiple contractile vacuoles represents its most unique feature and distinguishes it from all other described Ophryoglena spp. The number of somatic kineties of O. hemophaga (range 50 to 62) is also a distinguishing feature, since it is the lowest described from any Ophryoglena sp. Other characteristics of this species include: ovoid to elongate trophonts 96 to 288 μm in length, with an elongate macronucleus 41 to 65 μm in length; tomonts 50 to 150 μm in diameter producing a clear mucous cyst envelope, whose thickness is approximately half of the tomont diameter; elongated theronts 96 to 131 μm in length which emerge after 1 to 3 cell divisions taking 36 to 48 h at 20 ± 3°C. Protomonts and theronts are, respectively, negatively and positively phototactic - characteristics that likely aid in maintenance of infection in zebra mussel populations. © Inter-Research 2005.