Revision of Gangesia (Cestoda: Proteocephalidea) in the Indomalayan Region: Morphology, Molecules and Surface Ultrastructure

Abstract

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.

An annotated list of the species of Gangesia Woodland, 1924 (Cestoda: Proteocephalidea), parasites of catfishes in Asia, with new synonyms and a key to their identification

“…The present revision is based on a morphological evaluation of the type-specimens and vouchers from museum collections as well as newly collected material (see 'Material studied' for each individual species from the Palaearctic Region; for data on the extensive material studied for each species from the Indomalayan Region, see Ash et al, 2012). Most specimens were collected from fish hosts sold in fish markets or provided by local fishermen.…”

“…This implies that these hosts were destined for human consumption and thus no collection permits were needed. Fish that were still alive were killed by dorsal pithing (spinal cord and blood vessels being cut immediately behind the head), a method used to ameliorate the suffering of animals recommended by law in the Czech Republic, the European Directive and local animal care committees (see Ash et al, 2012).…”

“…Subsequently, Gangesia became one of the most species-rich genera of proteocephalidean cestodes with about 50 nominal species, most having been described from India. However, only four of 48 nominal species of Gangesia reported from this region, including several species mistakenly placed in Silurotaenia Nybelin, 1942, were considered to be valid by Ash et al (2012), who evaluated newly collected material using both morphological and molecular data. A study of additional specimens collected in China, Japan and Russia, supplemented by a study of type-and voucher material of all of the Palaearctic species, made a complete revision of the genus possible.…”

A new genus and species of proteocephalidean tapeworm (Cestoda), first parasite found in the driftwood catfish Tocantinsia piresi (Siluriformes: Auchenipteridae) from Brazil

“…Out of the nine specimens found, five were fixed with hot 4% neutral formaldehyde solution and subsequently stored in 70% ethanol (see de Chambrier et al 2014). A small piece of the posterior end of the four remaining specimens was cut off and placed in molecular-grade 96-99% ethanol for sequencing of the 28S rRNA gene (for methodology, see Ash et al 2012). For morphology, specimens were stained with Mayer's hydrochloric carmine solution, dehydrated in an ethanol series, cleared with eugenol (clove oil) and mounted in Canada balsam.…”

“…Mehlis' gland about 70-100 in diameter, representing 4-7% of proglottid width (n = 11). Relative ovarian size (see de Chambrier et al 2012) about 15% of size of mature and pregravid proglottids.…”