First morphological and molecular characterization of cystacanths of Corynosoma evae Zdzitowiecki, 1984 (Acanthocephala: Polymorphidae) from Antarctic teleost fishes

Redescription and molecular analysis of Corynosoma pseudohamanni Zdzitowiecki, 1984 (Acanthocephala: Polymorphidae) juveniles from Notothenia coriiceps Richardson in the water area of Argentine Islands, West Antarctica

Corynosoma pseudohamanni Zdzitowiecki, 1984 (Polymorphidae) was described from the intestinal tract of 5 species of seals including the type and main host, the Weddell seal Leptonycotes weddellii (Lesson) in the South Shetlands, West Antarctica. Notothenia coriiceps was the primary paratenic host of 14 fish hosts reported in the original description. We describe excysted juveniles from the body cavity of the major paratenic host, Notothenia coriiceps Richardson collected off Galindez Island, Argentine Islands, West Antarctica for the first time. The original description was not "based on material collected from the final hosts (seals) and paratenic hosts (fish)" as stated since no description of juveniles was given then. Our excysted juveniles were generally smaller than reported adults and many of the other measurements were comparable to those of the adults in the original description. We added many of the incomplete measurements of adults in the original description especially those of the underdeveloped reproductive structures. We compared our morphometric description with the only other one available for juveniles collected from three paratenic fish hosts from Prince Gustav Channel, Antarctica. We have added informative optical microscopy images and SEM images of internal and external structures, previously missed in the original description. Energy Dispersive X-ray analysis revealed the highest levels of calcium in all hooks and hook roots compared to sulfur and phosphorus. We also provide a molecular characterization of the species for the first time. Newly generated sequences of the mitochondrial cytochrome c oxidase subunit 1 (mtcox1) gene from isolates of C. pseudohamanni cystacanths were compared with sequences of other acanthocephalans available in GenBank. Phylogenetic analyses based on maximum likelihood (ML) and Bayesian inference (BI) methods of the cox1 dataset placed all the species of Corynosoma in a single clade, with strong support. The mt cox1 sequences of C. pseudohamanni formed a strongly supported individual clade with the published sequences of Corynosoma nortmeri and Corynosoma magdaleni from the North Sea, Germany. We have determined the genetic diversity of C. pseudohamanni and compare it with other Corynosoma species haplotype diversity and distribution.

Morphological description and molecular characterization of Heterospinus mccordi n. gen. n. sp. (Acanthocephala: Polymorphidae) from cystacanths infecting a non-native crayfish host, Procambarus clarkii (Decapoda: Cambaridae), in South Carolina, USA

A new genus and species within the family Polymorphidae Meyer, 1931 were erected to accommodate cystacanths recovered from the mesentery of individuals from a non-native population of the red swamp crayfish Procambarus clarkii (Girard), collected from South Carolina (USA). Morphological characteristics of the specimens collected included in both sexes a spindle-shaped body with a slender hindtrunk, two fields of markedly different sized spines on the foretrunk, the presence of a middle row of smaller scythe-shaped hooks on a proboscis armed with 19-20 longitudinal rows of 14-16 hooks; and in males, six cement glands, absence of genital spines, and a digitiform and spinose bursa (observed inverted). Sequencing portions of both the mitochondrial cytochrome c oxidase I (COI) and large subunit ribosomal RNA genes was completed, followed by phylogenetic analysis of a concatenated alignment. Sequences from our specimens appeared in a clade with those of Hexaglandula corynosoma (Travassos, 1915) and Ibirhynchus dimorpha (Schmidt, 1973) but were 27% divergent from both using the COI marker. The genetic divergence of this parasite from other polymorphid genera, along with unique morphological features, justified erecting a new genus and new species. Herein we describe Heterospinus mccordi n. gen. n. sp. bringing the total number of genera within the family Polymorphidae to 16, and we emend and update the latest key that was provided for the genera within this family. This is the first record of polymorphids infecting P. clarkii outside of its native range. The definitive host remains unknown.

Helminth fauna of the black goby Gobius niger L. (Gobiiformes: Gobiidae) from the Finnish Archipelago, Baltic Sea: Molecular and morphological data

Black gobies (Gobius niger) from the Finnish Archipelago, Baltic Sea, were screened for helminth infections in summer 2020. Helminths were identified morphologically and/or molecularly. Altogether 26 novel sequences were generated and analysed using maximum likelihood estimation. Morphological and phylogenetic analyses based on mitochondrial genes revealed the presence of 8 species belonging to the Digenea (Diplostomum mergi Lineage 3), Cestoda (Bothriocephalus scorpii), Nematoda (Contracaecum rudolphii A, Cucullanus sp. and Hysterothylacium aduncum), and Acanthocephala (a putative new species of Corynosoma, Corynosoma semerme and Neoechinorhynchus sp.). Phylogenetic and comparative sequence analyses revealed that the putative new acanthocephalan species is closely related to C. neostrumosum described from the Caspian seal, Pusa caspica, in the Caspian Sea. The black goby represents a new host record for four parasite species (Diplostomum mergi Lineage 3, Contracaecum rudolphii A, Corynosoma semerme and Corynosoma sp.). The Finnish Archipelago is a novel locality record for three species (Corynosoma sp., Diplostomum mergi Lineage 3 and Bothriocephalus scorpii).

Acanthocephalans of marine and freshwater fishes from Taiwan with description of a new species

During an ichthyoparasitological survey in 2017-2019, six species of acanthocephalans were found among Taiwan's freshwater (Cypriniformes: Xenocyprididae, Cyprinidae) and marine fishes (Scombriformes: Scombridae, Trichiuridae; Anabantiformes: Channidae; Carangaria/misc: Latidae): Micracanthorhynchina dakusuiensis (Harada, 1938), Rhadinorhynchus laterospinosus Amin, Heckmann et Ha, 2011, Pallisentis rexus Wongkham et Whitfield, 1999, Longicollum sp., Bolbosoma vasculosum (Rudolphi, 1819), and one new species, Micracanthorynchina brevelemniscus sp. n. All species are morphologically characterised and illustrated using light and scanning electron microscopy. The finding of R. laterospinosus, P. rexus and B. vasculosum is the first record for these species in Taiwan. Micracanthorhynchina brevelemniscus is similar to Micracanthorhynchina motomurai (Harada, 1935) and M. dakusuiensis in proboscis armature but differs from M. motomurai by larger eggs (53-59 × 15-16 µm vs 40 × 16 µm) and by the number of cement glands (6 vs 4) and from M. dakusuiensis by shorter body length (2.2-2.9 mm vs 4.0 mm in males and 2.9-4.1 mm vs 7.6 mm in females), by the location of the organs of the male reproductive system (from level of the posterior third of the proboscis receptacle in M. brevelemniscus vs in the posterior half of the trunk in M. dakusuiensis), and by length of lemnisci (lemnisci shorter than the proboscis receptacle vs lemnisci longer than the proboscis receptacle). Phylogenetic analyses of almost complete 18S rRNA gene revealed paraphyly of the family Rhadinorhynchidae suggested in previous studies. Micracanthorhynchina dakusuiensis and M. brevelemniscus formed a strongly supported cluster, which formed the earliest diverging branch to the rest of the rhadinorhynchids and transvenids.

Loss of species and genetic diversity during colonization: Insights from acanthocephalan parasites in northern European seals

Studies on host-parasite systems that have experienced distributional shifts, range fragmentation, and population declines in the past can provide information regarding how parasite community richness and genetic diversity will change as a result of anthropogenic environmental changes in the future. Here, we studied how sequential postglacial colonization, shifts in habitat, and reduced host population sizes have influenced species richness and genetic diversity of Corynosoma (Acanthocephala: Polymorphidae) parasites in northern European marine, brackish, and freshwater seal populations. We collected Corynosoma population samples from Arctic, Baltic, Ladoga, and Saimaa ringed seal subspecies and Baltic gray seals, and then applied COI barcoding and triple-enzyme restriction-site associated DNA (3RAD) sequencing to delimit species, clarify their distributions and community structures, and elucidate patterns of intraspecific gene flow and genetic diversity. Our results showed that Corynosoma species diversity reflected host colonization histories and population sizes, with four species being present in the Arctic, three in the Baltic Sea, two in Lake Ladoga, and only one in Lake Saimaa. We found statistically significant population-genetic differentiation within all three Corynosoma species that occur in more than one seal (sub)species. Genetic diversity tended to be high in Corynosoma populations originating from Arctic ringed seals and low in the landlocked populations. Our results indicate that acanthocephalan communities in landlocked seal populations are impoverished with respect to both species and intraspecific genetic diversity. Interestingly, the loss of genetic diversity within Corynosoma species seems to have been less drastic than in their seal hosts, possibly due to their large local effective population sizes resulting from high infection intensities and effective intra-host population mixing. Our study highlights the utility of genomic methods in investigations of community composition and genetic diversity of understudied parasites.