Revision of Gangesia (Cestoda: Proteocephalidea) in the Indomalayan region: morphology, molecules and surface ultrastructure

Tapeworms of Gangesia Woodland, 1924 (Cestoda: Proteocephalidea) parasitic in freshwater fishes in the Indomalayan Region were critically reviewed. Evaluation of type specimens and newly collected materials from Bangladesh, Cambodia and India, as well as critical examination of extensive literature have shown that only the following four species, instead of 48 nominal species of Gangesia and Silurotaenia Nybelin, 1942 reported from this region (36 new synonymies proposed), are valid: Gangesia bengalensis (Southwell, 1913), type-species of the genus and most common parasite of Wallago attu (Siluridae), G. macrones Woodland, 1924 typical of Sperata seenghala (Bagridae), both species characterized by the possession of two circles of hooks on the rostellum-like organ and several rows of hooklets on the anterior margins of suckers; G. agraensis Verma, 1928 from W. attu (typical host), which has the scolex with only one circle of hooks and 1-3 incomplete rows of tiny hooklets on the suckers; and G. vachai (Gupta and Parmar, 1988) n. comb. from several catfishes, which possesses 4-6 circles of hooks and 5-11 rows of hooklets on the anterior half of suckers. Scolex morphology, including surface ultrastructure (microtriches), of all but one species (G. vachai) is described for the first time using scanning electron microscopy. A phylogenetic analysis based on the partial sequences encoding the large nuclear ribosomal subunit RNA gene has shown that three Indomalayan species, namely G. bengalensis, G. macrones and G. vachai, form a monophyletic group within Gangesia, whereas G. agraensis tends to form a clade with the Palaearctic species of the genus. A table with differential characters of all species from the Indomalayan Region is also provided together with a key to identification of genera of the subfamily Gangesiinae. The present study demonstrates that species of Silurotaenia do not occur in the Indomalayan region.