Description of a new species of Podocotyle Dujardin, 1845 (Digenea: Opecoelidae: Plagioporinae) from the cusk-eel, Luciobrotula corethromycter Cohen, 1964 (Ophidiiformes: Ophidiidae), from the Gulf of Mexico and Caribbean Sea

Molecular and morphological screening of Podocotyle spp. (Trematoda: Opecoelidae) sheds light on their diversity in Northwest Pacific and eastern European Arctic

Podocotyle is a genus of marine opecoelid digeneans that parasitize a wide variety of fish as adults. We present the first phylogenetic analysis of several Podocotyle isolates using nuclear 28S rDNA and mitochondrial cox1 DNA regions. New sequences were obtained for Podocotyle specimens from fish caught in the Sea of Okhotsk and the White Sea. Based on morphological and molecular data, eight Podocotyle lineages of species rank were revealed. However, this diversity is poorly formalized within the current taxonomic model of the genus. As a result, we identified Podocotyle cf. angulata, Podocotyle cf. atomon, Podocotyle cf. reflexa, Podocotyle atomon of Sokolov et al., 2019, Podocotyle sp. of Denisova et al., 2023, Podocotyle sp. 1, Podocotyle sp. 2 and Podocotyle sp. 3. We also highlight the unresolved question of the life cycles of representatives of Podocotyle whose intramolluscan stages parasitize the intertidal snails Littorina spp.

Digenean parasites of deep-sea teleosts: A progress report

The developments in the study of digeneans of deep-sea fish in the 21st Century are documented and discussed. Most recent work has been on the bathyal fauna (i.e. 1,000m-2,999 m depth), with virtually nothing on the abyssal fauna (i.e. deeper than 3,000 m). The one study on hydrothermal vent digeneans has indicated that these regions probably harbour a distinctive fauna. The demarcation of the deep-sea fauna is blurred at the poles, where the cold-adapted fauna appears similar to the shallower bathyal fauna. The abyssal fauna, however, appears distinct, possibly due to adaptations to variable or ultra-high pressures. The digenean fauna of bathypelagic fishes is depauperate. Recent phylogenetic studies reinforce the view that the typical deep-sea fauna has radiated in the deep-sea. Encroachment into the deep from shallow water is relatively rare. Overall, the digenean fauna in the deep-sea is distinctly less diverse that the equivalent fauna in shallow waters. A major conclusion is that our understanding of the deep-sea digenean fauna is poor, and that much further work over a much wider area is needed.

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Sampling effort in the deep-sea is poor and restricted to a few areas.

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Deep-sea digenean diversity is distinctly lower than in shallow water.

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Much of the deep-sea digenean fauna appears to have radiated in the deep-sea.

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Encroachment into the very deep sea from shallow waters is rare.

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Adaptation to cold temperature appears to be a major factor in deep-sea digeneans.

Intermediate host switches drive diversification among the largest trematode family: evidence from the Polypipapiliotrematinae n. subf. (Opecoelidae), parasites transmitted to butterflyfishes via predation of coral polyps

Podocotyloides stenometra Pritchard, 1966 (Digenea: Opecoelidae) is the only trematode known to infect anthozoan corals. It causes disease in coral polyps of the genus Porites Link (Scleractinia: Poritidae) and its life-cycle depends on ingestion of these polyps by butterflyfishes (Perciformes: Chaetodontidae). This species has been reported throughout the Indo-Pacific, from the Seychelles to the Galápagos, but no study has investigated whether multiple species are involved. Here, we recollect P. stenometra from its type-host and type-locality, in Hawaiian waters, and describe four new species from examination of 768 butterflyfishes from French Polynesia. On the basis of morphology, phylogeny and life-history, we propose Polypipapiliotrema Martin, Cutmore & Cribb n. gen. and the Polypipapiliotrematinae Martin, Cutmore & Cribb n. subf., for P. stenometra (Pritchard) n. comb., P. citerovarium Martin, Cutmore & Cribb n. sp., P. hadrometra Martin, Cutmore & Cribb n. sp., P. heniochi Martin, Cutmore & Cribb n. sp., and P. ovatheculum Martin, Cutmore & Cribb n. sp. Given the diversity uncovered here and the ubiquity, abundance and diversity of butterflyfishes on coral reefs, we predict that Polypipapiliotrema will prove to comprise a rich complex of species causing disease in corals across the Indo-Pacific. The unique life-cycle of these taxa is consistent with phylogenetic distinction of the group and provides evidence for a broader basis of diversification among the family. We argue that life-cycle specialisation, in terms of adoption of disparate second intermediate host groups, has been a key driver of the diversification and richness of the Opecoelidae, the largest of all trematode families and the group most frequently encountered in coral reef fishes.