Morphological, Ultrastructure and Histological Studies of A Parasitic Ciliate, Conchopthirus steinae n.sp. (Protozoa: Protista: Ciliophora) in a Freshwater Bivalve Mussel, Lamellidens marginalis (Mollusca: Bivalvia: Unionidae), from South 24 Parganas

Conchopthirus spp. (Stein, 1861) is a parasitic ciliate that infects several species of freshwater bivalve molluscs. They are known to cause infection in the visceral mass, mantle and gill tissues of the malacofauna. It shares an obligate symbiotic relationship with its host and generally dies within a few hours of separation. In the present study, Compound Microscopy was carried out using silver impregnation method. The parasite has a dorsoventrally-flattened body, leaf-shaped in outline with pointed anterior and rounded posterior ends. Dense ciliary rows are present all over the body surface. The macronucleus is large, rounded-shape and placed at the posterior end of the body. Ultra structure of the parasite shows a dorsoventrally fattened body with dense cilia covering the body surface. Histological studies showed the infection of the parasite on the gill tissue of the host. The parasite shows similarity with a similar species of the same Genus Conchopthirus acuminatus but is quite different in several features including the morphometry and location of the macronucleus. This novel species Conchopthirus steinae n.sp. has been identified by its morphological and Scanning Electron Microscopic studies in a freshwater bivalve mussel Lamellidens marginalis (Lamark 1819), for the first time in South 24 Parganas District, West Bengal.