Studies on gorgoderid digeneans from Australian and Assian Freshwater fishes

Molecular phylogenetic position and the life cycle of Phyllodistomum cyprini Feng et Wang, 1995 in Japan, with a note of a larval Phyllodistomum sp. from unionid mussels in North America

A gorgoderid species, Phyllodistomum cyprini Feng et Wang, 1995 obtained from ureters of common carp, Cyprinus carpio in Japan is described both morphologically and molecularly. Its larval stage is a macrocercous cercaria found in a unionid mussel, Nodularia nipponensis first described by Urabe et al. (2015). A molecular phylogenetic study revealed that P. cyprini is not closely related to rhopalocercous cercariae from unionid mussels both in Europe and North America. This result indicates that there are several distinct clades in Phyllodistomum species that use unionid mussels as a first intermediate host, and suggests that the cercarial morphology may be a more accurate indicator of the phylogeny of Phyllodistomum than molluscan host identity.

Genetic characterization and phylogenetic relationships of Phyllodistomum parasites in Indian subcontinent: insights from freshwater fish and shrimp hosts

Phyllodistomum is the large digenean group of fish parasites, with 25 species described so far in the Indian subcontinent. Here, we redescribed two adult species of Phyllodistomum (P. srivastava Rai 1964 and P. parorchium Jaiswal 1957) collected from freshwater fish Heteropneustes fossilis Bloch, 1974 and Glossogobius giuris Ham, 1822, respectively, and an unknown Phyllodistomum metacercaria from shrimp (Macrobrachium dayanum Henderson, 1893). These parasites were genetically characterized using 28S and first and second internal transcribed spacers (ITS1 and ITS2) regions of the nuclear ribosomal DNA and CoxI region of the mitochondrial (mt) DNA to establish the link between metacercaria and adult. Morphologically, both the unknown metacercaria in shrimp and adult Phyllodistomum srivastava in fish, resembled in terms of crenulated margin of hind body, arrangement of diagonal testes, bipartite seminal vesicle, and compact paired vitelline masses. The two adult parasite species, P. srivastava from P. parorchium, were different in terms of shape and size of the body, ratio of suckers, the absence of crenulated margin of hind body, a single chambered seminal vesicle, and deeply lobed paired vitelline masses, in the former species. Comparison of the 28S, ITS, and mtCoxI sequence data suggested P. srivastava and Phyllodistomum metacercaria belong to the same species, and supported the distinction between P. srivastava and P. parorchium. Exploring the potential impact of Phyllodistomum infection on host behaviour and health would be prospective areas for future research.

The life cycle and molecular phylogeny of a gorgoderid trematode recorded from the mussel Nodularia douglasiae in the Yodo River, Japan

In 2009, a novel larval trematode of the family Gorgoderidae was found in the gonads of Nodularia douglasiae (Unionidae) from the lower reaches of the Yodo River, Osaka Prefecture, Japan. This is the first collection of trematodes in a unionid mussel in Japan. We investigated the morphology and life cycle of the trematode, and conducted a molecular phylogenetic analysis with other gorgoderid species, both those collected in the Yodo River water system and those reported in the literature. Immature adult worms were obtained from the ureters of the common carp Cyprinus carpio, the first known instance of a gorgoderid from these fish in Japan. Morphological characteristics and molecular data show that it belongs to the subfamily Gorgoderinae (genus Phyllodistomum sensu lato). Regarding the morphology, first intermediate host, and the infection site of adult worms, it resembles Phyllodistomum elongatum Nybelin, 1926 from Europe, but no comparable molecular data exist for Ph. elongatum. Three cytochrome c oxidase subunit I haplotypes were detected in the specimens analyzed, suggesting that the present species is indigenous to the Yodo River water system. The 28S ribosomal DNA data showed that this species is a member of the clade consisting of Ph. cf. symmetorchis, Ph. folium, Pseudophyllodistomum and Xystretrum. However, its phylogenetic position within the clade differs between the maximum likelihood and maximum parsimony trees, and the sister species of the present species remain unclear.

Phylogenetic relationships of the Gorgoderidae (Platyhelminthes: Trematoda), including the proposal of a new subfamily (Degeneriinae n. subfam.)

Phylogenetic analyses of a range of gorgoderid trematodes based on ITS2 and partial 28S rDNA data lead us to propose the Degeneriinae n. subfam. for the genus Degeneria in recognition of its phylogenetic isolation and distinctive morphology and biology. The current concepts of the subfamilies Anaporrhutinae and Gorgoderinae were supported. Within the Gorgoderinae, the large genus Phyllodistomum is shown to be paraphyletic relative to Pseudophyllodistomum and Xystretrum. Notably, the clade of marine Phyllodistomum does not form a clade with the other marine genus, Xystretrum. Distinct clades within the Gorgoderinae correspond variously to identity of first intermediate host, form of cercaria and their marine or freshwater habitat. We are not yet in a position to propose separate genera for these clades.

Intra-specific variation of Kudoa spp. (Myxosporea: Multivalvulida) from apogonid fishes (Perciformes), including the description of two new species, K. cheilodipteri n. sp. and K. cookii n. sp., from Australian waters

Kudoa spp. from the musculature and intestinal mucosa of species of the teleost family Apogonidae were examined for their taxonomic identity. Two novel species are characterised: Kudoa cheilodipteri n. sp. from the musculature of Cheilodipterus quinquelineatus Cuvier, Ostorhinchus cyanosoma (Bleeker) and O. aureus (Lacépède); and Kudoa cookii n. sp. from the submucosa of the intestines of O. cookii (Macleay) only. Both species are characterised using morphology, small subunit ribosomal DNA (SSU rDNA), large subunit ribosomal DNA (LSU rDNA), and biological characters. Three new host records, O. cyanosoma, O. aureus and Apogon doederleini, and associated geographical, morphological and genetic data are also provided for Kudoa whippsi Burger & Adlard, 2010. Morphological and molecular intra-specific variation of all isolates assigned to K. whippsi is also examined. Phylogenetic analyses further support the idea that tissue tropism is a distinguishing character between morphologically similar species; species reported here display close relatedness to morphologically similar species infecting the same tissue within their hosts.

Richness and diversity of macroparasite communities in tropical eels Anguilla reinhardtii in Queensland, Australia

The prediction that richness and diversity of helminth communities would be greater in tropical fish was tested by analysing total and intestinal helminth communities in samples of Anguilla reinhardtii taken from 10 localities in tropical and semi-tropical freshwaters in Queensland, Australia. Comparison of findings with those from A. anguilla in the UK revealed that regional species richness was higher in Queensland and that helminth communities harboured a suite of common species, virtually all eel specialists, that were responsible for the observed higher levels of similarity between component communities. All measures of community richness and diversity adopted indicated that the poorest helminth communities in A. reinhardtii were comparable with the richest ones reported from the northern temperate A. anguilla. The richest communities in A. reinhardtii were more diverse than those reported from any other species of fish, whether marine or freshwater, to date, and were comparable with the communities found in some species of aquatic birds. Both tropical conditions and age and endemism of the host, i.e. the time hypothesis, were considered as explanations for this richness but neither could be favoured. A cautious approach to generalizations based on data from temperate regions only is advocated, and the need for more studies on tropical parasite communities is strongly emphasized.

The phylogenetic position of Allocreadiidae (Trematoda: Digenea) from partial sequences of the 18S and 28S ribosomal RNA genes

Species of Allocreadiidae are an important component of the parasite fauna of freshwater vertebrates, particularly fishes, and yet their systematic relationships with other trematodes have not been clarified. Partial sequences of the 18S and 28S ribosomal RNA genes from 3 representative species of Allocreadiidae, i.e., Crepidostomum cooperi, Bunodera mediovitellata, and Polylekithum ictaluri, and from 79 other taxa representing 78 families of trematodes obtained from GenBank, were used in a phylogenetic analysis to address the relationships of Allocreadiidae with other plagiorchiiforms/plagiorchiidans. Maximum parsimony and Bayesian analyses of combined 18S and 28S rRNA gene sequence data place 2 of the allocreadiids, Crepidostomum cooperi and Bunodera mediovitellata, in a clade with species of Callodistomidae and Gorgoderidae, which, in turn is sister to a clade containing Polylekithum ictaluri and representatives of Encyclometridae, Dicrocoelidae, and Orchipedidae, a grouping supported by high bootstrap values. These results suggest that Polylekithum ictaluri is not an allocreadiid, a conclusion that is supported by reported differences between its cercaria and that of other allocreadiids. Although details of the life cycle of callodistomids, the sister taxon to Allocreadiidae, remain unknown, the relationship of Allocreadiidae and Gorgoderidae is consistent with their larval development in bivalve, rather than gastropod, molluscs, and with their host relationships (predominantly freshwater vertebrates). The results also indicate that, whereas Allocreadiidae is not a basal taxon, it is not included within the suborder Plagiorchiata. No support was found for a direct relationship between allocreadiids and opecoelids either.

First report of intramolluscan stages of a gorgoderid digenean from a marine bivalve

A survey of bivalves from Heron Island on the Great Barrier Reef, Australia, revealed a novel digenean infection in Lioconcha castrensis (Bivalvia: Veneridae). The cercaria has oral and ventral suckers, a dorsoventrally orientated stylet embedded in the oral sucker, penetration glands, and a large tail that is inflated at its base. This morphology is broadly consistent with that of previously described gorgoderid cercariae. Partial large subunit ribosomal RNA gene (D1-D3 domains) was sequenced and aligned with sequences from other gorgoderids and related families. Phylogenetic analysis also suggests that the species belongs to the Gorgoderinae. To our knowledge, this is the first report of a gorgoderid from a marine bivalve.

Questions in digenean systematics and evolution

Since the work of Dujardin (1845), attempts have been made to decipher acceptable divisions of the trematode groups at higher taxonomic levels, and yet there is still no generally accepted classification of the higher taxa of the Trematoda as there are for other groups of parasitic worms, such as the Monogenea, Cestoda, Nematoda and Acanthocephala. Why is it that workers with a wide knowledge of trematode systematics, such as Dollfus, Stunkard, Manter and especially Yamaguti, have felt unable or unwilling to comment in detail upon the phylogenetic relationships within the group at higher taxonomic levels? One of the main reasons for this state of affairs lies in the fact that, generally speaking, the group is not easily split into major subgroups by obvious, non-homoplasious morphological characters. Early attempts at division, based upon sucker arrangements, i.e. monostome, distome, amphistome and gasterostome, are not satisfactory, as distomes form the vast majority of the Digenea and both monostomes and amphistomes are certainly polyphyletic. In addition, the picture within the Digenea is complicated by the group's complex life-history patterns. Whereas early classifications all tended to be based upon adult (marital) morphology, life-history patterns are given great weight by workers such as Pearson (1972) and Bozhkov (1982). The cercarial morphology is considered the dominant feature in the classification of the group presented by La Rue (1957) and is emphasized in the phylogenetic relationships between the subgroups recognized by Cable (1974). Odening (1961), following an earlier suggestion of Lebour (1912), presented a classification, the major divisions of which were based upon the daughter-parthenita (i.e. the redia or daughter-sporocyst), a stance which he later found untenable (Odening, 1974). Consequently, the wealth of conflicting data from these and other sources has deterred the presentation both of classifications and speculations on evolutionary relationships. The classification of Odening (1974) and the recent cladistic analysis of Brooks, O'Grady & Glen (1985b) utilized data from all of the life-history stages. As the classification of Brooks et al. (1985b) is the most recent, and readily available in English, it must be a serious contender in terms of general acceptance. If it is accepted, then one would hope that this will be on its merits rather than because of its availability or the lack of viable alternatives; but, as discussed below, it is easy to find fault with this classification when it and its premises are examined in detail.