Archigetes Leuckart, 1878 (Cestoda, Caryophyllidea): diversity of enigmatic fish tapeworms with monoxenic life cycles

The caryophyllidean genus Archigetes Leuckart, 1878 is unique among all tapeworms in that its species can mature in invertebrate hosts (Oligochaeta), i.e., have a monoxenic (direct) life cycle. All five species were described as progenetic plerocercoids in oligochaetes and two of them also as adults from cypriniform fishes. Two species, A. sieboldi Leuckart, 1878 and A. iowensis Calentine, 1962, were found in North America in non-native common carp (Cyprinus carpio). A molecular study of caryophyllideans from the southern United States has revealed the occurrence of three new species in native freshwater fishes (Catostomidae, Ictiobinae): Archigetes loculotruncatus n. sp. from Ictiobus bubalus, I. niger and Carpiodes cyprinus is the largest representative of the genus and differs by a loculotruncate scolex. Archigetes megacephalus n. sp. from Ictiobus niger, I. bubalus and I. cyprinellus is characterised by a prominent, bothrioloculodiscate scolex. Archigetes vadosus n. sp. from I. bubalus is typified by a globular scolex with very shallow loculi; it differs from the closely related A. sieboldi in the shape of the body, with a distinct neck region and a scolex wider than the remaining body. Archigetes iowensis Calentine, 1962 becomes a junior synonym of Paraglaridacris limnodrili (Yamaguti, 1934). The generic diagnosis of Archigetes is amended and a key to identification of North American taxa is provided. Species of Archigetes and Paraglaridacris differ from each other most conspicuously in the structure of the ovary, which is follicular in Archigetes versus compact in Paraglaridacris.

Molecular evidence of three closely related species of Biacetabulum Hunter, 1927 (Cestoda: Caryophyllidea): a case of recent speciation in different fish hosts (Catostomidae)?

Monozoic tapeworms (Caryophyllidea) are dominant components of parasite communities of suckers (Catostomidae) in North America, with Biacetabulum Hunter, 1927 representing one of the more species-rich genera. Molecular (28S rDNA) and morphological (including scanning electron microscopy and histology) evaluation of newly collected tapeworms from different fish hosts revealed the existence of four similar (and three closely related) species of Biacetabulum. These four species differ from their congeners by having a long body (up to 48 mm long) with a very long, slender neck (its length represents ≥30% of total body length), a large, globular scolex with a prominent central acetabulum-like loculus on the dorsal and ventral sides, two pairs of shallow lateral loculi and a distinct, slightly convex apical disc, and a cirrus-sac that is situated between the anterior arms of the ovarian wings. Taken together, the morphological and molecular data and the host associations of these species provide evidence of their host specificity. Biacetabulum isaureae n. sp. occurs in notch clip redhorse, Moxostoma collapsum, in South Carolina (USA), B. longicollum n. sp. in silver redhorse, Moxostoma anisurum (type host), and golden redhorse, M. erythrurum, in Manitoba (Canada) and West Virginia (USA), B. overstreeti n. sp. in a spotted sucker, Minytrema melanops, in Mississippi, and B. hypentelii n. sp. in northern hogsucker, Hypentelium nigricans, in Tennessee (USA). The new species differ from each other in the number of postovarian vitelline follicles, the posterior extent of preovarian vitelline follicles and relative size of the cirrus sac.

Disentangling taxonomy of Biacetabulum (Cestoda, Caryophyllidea), parasites of catostomid fishes in North America: proposal of Megancestus gen. n. to accommodate B. carpiodi

A new genus, Megancestus n. gen., is proposed to accommodate the caryophyllidean tapeworm Biacetabulum carpiodi Mackiewicz, 1969 from carpsuckers and quillback (Carpiodes spp.) in North America. This species is not closely related to other species of Biacetabulum Hunter, 1927 and is transferred to a newly erected genus. This new genus is typified by the possession of a small body (total length of 3.1-7.5 mm) with a scolex that bears a pair of large acetabulum-like loculi, two pairs of shallow lateral loculi, and a slightly convex apical disc, testes arranged in one or two layers, oval, thick-walled cirrus-sac, well-developed external seminal vesicle, separate gonopores, H-shaped ovary, few median vitelline follicles, and the uterus extending by a single loop anterior to the cirrus-sac. Megancestus differs from all Nearctic caryophyllidean genera (family Capingentidae), including Biacetabulum, by vitelline follicles dorsal to the ovary that connect the preovarian and postovarian vitelline fields. The most closely related Hunterella Mackiewicz et McCrae, 1962 differs by shape of the scolex (tholate, i.e., devoid of any loculi), dumbbell-shaped ovary and the uterus not extending anterior to the cirrus-sac. Megancestus carpiodi (Mackiewicz, 1969) n. comb. is the only species of the genus and it is a stenoxenous parasite, which has been found only in the river carpsucker (Carpiodes carpio-type host), quillback (Carpiodes cyprinus) and highfin carpsucker (Carpiodes velifer) (Catostomidae: Ictiobinae) in the lower and middle Mississippi basin.

Phylogenetic reconstruction of early diverging tapeworms (Cestoda: Caryophyllidea) reveals ancient radiations in vertebrate hosts and biogeographic regions

Tapeworms of the order Caryophyllidea are the earliest diverging 'true' tapeworms (Eucestoda) and parasitise cypriniform and siluriform fishes almost exclusively. They are typified by a monozoic (non-proglottised) body plan, which is a characteristic shared with early diverging 'cestodarians' Gyrocotylidea and Amphilinidea. Here we present the most comprehensive multi-gene molecular phylogeny of this group, to date. Specimens of 63 species from 32 genera (~50% and ~75% of known species and genus diversity, respectively) were gathered during an intense and targeted 15-year collecting effort. Phylogenetic reconstructions provide high nodal support for three major lineages, which only partly correspond to currently recognised families. The three well-supported clades were as follows: Clade A was in an unsupported position at the base of the tree and was almost exclusively comprised of parasites of catfishes (Siluriformes) from the Afrotropical and Indomalayan regions, including the type genus of the Lytocestidae (Lytocestus). Clade B formed the sister group to the remaining taxa (Clade C) and was composed of species that parasitise cyprinids and loaches (Cypriniformes: Cyprinoidei and Cobitoidei) from the Palaearctic Region. This clade included the type genus of the Caryophyllaeidae (Caryophyllaeus). Clade C comprised Nearctic species from suckers and minnows (Cypriniformes: Catostomidae and Cyprinoidei), which were previously accommodated in two families, i.e. Capingentidae and Caryophyllaeidae. This clade included the type genus of the Capingentidae (Capingens). In addition to Clades A-C, Balanotaenia bancrofti from the monotypic Balanotaeniidae, which parasitises plotosid catfishes in Australia, and Lytocestoides tanganyikae, which parasitises African cichlids, formed a poorly supported clade at the base of the tree. Whereas morphological characteristics traditionally used to differentiate caryophyllidean families do not characterise molecular lineages, host association and biogeographical distribution play a key role in the circumscription of the three well-supported clades revealed by molecular data. Thus, the taxonomic rearrangement proposed herein was guided by the molecular clades. The names of all four extant families were preserved and family affinity was determined by topological clustering with the type genera of the families. The family diagnoses of the Lytocestidae, Caryophyllaeidae and Capingentidae are amended. Biogeographic patterns are indicative of separate Gondwanan and Laurasian radiations having taken place. Regarding the Gondwanan radiation in the Siluriformes, the topology in Clade A indicates an Asian origin with a subsequent African colonisation. Concerning Laurasia, separate radiations appear to have taken place in the Cypriniformes in the temperate zones of North America and Eurasia. Complete absence of caryophyllideans in the Neotropical Region, where numerous catfishes occur, may be due to the Gondwanan radiation having taken place after the continental separation of Africa and South America.

Morphological abnormalities in fish parasites: a potential tool for biomonitoring natural contaminants?

A comparative study on the strobilar morphology of the tapeworm Proteocephalus percae (Müller, 1780) (Cestoda), a parasite of the perch Perca fluviatilis (L.), showed a high percentage of abnormally developed parasite individuals. The evaluation of biological samples showed seven types of morphological abnormalities, mostly related to reproductive organs of the model tapeworm species. The most commonly identified deformity was an incomplete segmentation of the strobila. A malformed ovary, which is a structural anomaly linked with proglottization and maturation of the strobila, was also shown to be rather frequent. Offish hosts (P. percae) were collected from two localities with different levels of heavy metal pollution, the highly contaminated water reservoir Ružín and a control locality, the water reservoir Palcmanská Maša, which belongs to the European network of protected areas in Slovakia. Tapeworm abnormalities occurred more frequently in individuals from the contaminated environment (29.9%) compared with individuals from the control site (4.9%). The concentrations of heavy metals found in the parasites and their fish hosts from the heavily polluted reservoir support our assumption that the occurrence of abnormalities could be linked with the destructive effect of toxic substances. The present study also demonstrates that the enumeration of body deformities exceeding the common level of phenotypic variability of particular parasitic species could potentially be used as an indicator of environmental problems.

Diversity of monogeneans and tapeworms in cypriniform fishes across two continents

Cypriniformes, which exhibit a wide geographical distribution, are the most species-rich group of freshwater fishes. Despite considerable research on their parasites, no reliable estimates of their parasite diversity on a large geographical scale are available. In the present review, we analyse species richness of two parasitic flatworm groups (monogeneans and tapeworms) reported from cypriniform fishes in the two most intensively studied parts of the Holarctic region, Europe and North America. We also review knowledge on parasite speciation and host-parasite coevolution, and emphasise the risk of parasite co-introduction resulting from transfers of cypriniforms among different continents. As parasite diversity in European cypriniforms has been more intensively explored, we predicted a lower level of knowledge on parasite diversity in North American fishes, despite North America having a higher diversity of cypriniforms than Europe. Our data revealed a higher mean species richness of monogeneans and tapeworms per cypriniform species in Europe compared with North America. We showed that species richness of both parasite taxa in both continents is strongly affected by sample size, but that fish traits also play an important role in determining monogenean and tapeworm species richness in European cyprinoids. We recorded higher host specificity for cypriniform parasites in North America, even within parasite genera shared by cypriniforms on both continents. The host range of monogeneans parasitising cyprinoids on both continents was affected by phylogeny, indicating an effect of parasite life history on host specificity. The difference in parasite host range between the two continents could potentially be explained by either the low overall level of sampling activity in North America or an underestimation of parasite diversity in Europe. We suggest that future research efforts be focussed on cypriniforms in order to obtain reliable data for robust assessments of parasite species richness and phylogenies, to assess host-parasite coevolution and to reveal fish biogeography.

A New Classification of Glaridacris Cooper, 1920 (Cestoda: Caryophyllidea), Parasites of Suckers (Catostomidae) in North America, Including Erection of Pseudoglaridacris N. Gen

A taxonomic study of monozoic cestodes of the genus Glaridacris Cooper, 1920 (Cestoda: Caryophyllidea), parasites of catostomid fishes in North America, confirmed artificial character of the genus which is split to 2 different, morphologically distinct, and not closely related genera. Glaridacris is newly circumscribed to include only 3 species, Glaridacris catostomi Cooper, 1920 (type species), Glaridacris terebrans ( Linton, 1893 ), and Glaridacris vogei Mackiewicz, 1976 , which are characterized by an elongate body, a cuneiloculate or wedge-shaped scolex with 6 shallow loculi, male and female gonopores at a distance from each other, follicular ovary, and circum-medullary vitelline follicles (lateral and median). A new genus, Pseudoglaridacris n. gen., is proposed to accommodate 3 species characterized by a shorter body, a bothrioloculodiscate scolex with a pair of deeper median bothria and 2 shallower loculi, male and female gonopores close together, non-follicular ovary, and with only lateral vitelline follicles. The species are: Pseudoglaridacris laruei ( Lamont, 1921 ) n. comb. (type species), Pseudoglaridacris confusa (Hunter, 1929) n. comb., and Pseudoglaridacris oligorchis ( Haderlie, 1953 ) n. comb. An annotated list of all species of both genera, with data on their hosts and distribution and keys to their identification, is provided.