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Images and drawings of the new Gyrocotyle species. 2, Photomicrograph of Gyrocotyle haffii n. sp. holotype (NB: the specimen is immature) ex Harriotta raleighana, Goban Spur (13951/14); 3, Line-drawing of Gyrocotyle haffii n. sp., holotype; 4, Photomicrograph of Gyrocotyle discoveryi n. sp. holotype ex Hydrolagus mirabilis (Goban Spur; 15063/103a); 5. Line-drawing of Gyrocotyle discoveryi n. sp., holotype; 6, Gyrocotyle discoveryi n. sp. paratype ex Hydrolagus mirabilis (Goban Spur; 15066/124a). Scale-bars: 10 mm
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Chimaeras, or ratfishes, are the only extant group of holocephalan fishes and are the sole host group of gyrocotylidean cestodes, which represent a sister group of the true tapeworms (Eucestoda). These unique, non-segmented cestodes have been known since the 1850s and multiple species and genera have been erected despite a general agreement that th...
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Citations
... Necropsies of wild caught, sexually mature H. colliei maintained at POM often reveal tapeworms located in the spiral intestine, which are suspected to be Gyrocotyle based on their morphology and location within the host (Barčák et al., 2021;Karlsbakk et al., 2010;Simmons & Laurie, 1972). However, they are never found in captive-bred neonates and juveniles, indicating that this parasite cannot complete a developmental cycle in the chimera tanks at POM. Gyrocotylideans are widely spread among holocephalans but the identification of species among this group is a challenging task since it requires a fixation protocol that favors specimen relaxing and good preservation, and taxonomic expertise in this group (Barčák et al., 2021;Bray et al., 2020). Furthermore, we report that the parasitized specimens showed no necrosis or extended signs of inflammation around the flatworms' anchorings, and it seems unlikely that the parasites caused the death of the hosts. ...
The spotted ratfish Hydrolagus colliei is the most common holocephalan species exhibited in aquaria worldwide for introducing deep‐sea environments and raising awareness of their conservation. However, little is known about the biology of H. colliei. Current practices in aquaria allow long‐term survival of sexually mature H. colliei specimens; however, this species struggles to complete a reproductive cycle in captivity mostly because embryos do not reach the hatchling stage. The aquarists of Planet Ocean Montpellier (POM, France) have bred H. colliei for 15 years and recorded parameters suitable for this species' successful embryonic and post‐embryonic development. POM aquarists now regularly record egg‐laying events of H. colliei and use four tanks to incubate eggs and raise neonates, late hatchlings, early and intermediate juveniles, subadults, and sexually mature specimens. In this work we provide the first long‐term biometric data on H. colliei from the hatchling to the subadult stage. We also report the biotic and abiotic parameters sufficient to breed H. colliei in aquaria. We finally describe the methods used to facilitate individual monitoring of specimens along the ontogeny and several pathologies identified in this species, their putative causes, and the corresponding treatments. This work highlights the importance of ex situ research and points to the valuable outcomes of collaborative efforts between aquaria and academia in deciphering the biology of species whose study in the wild remains challenging.
... Identified specimens may be pooled per species (e.g., between 5-10 individuals or 30-90 individuals for gregarines) (Clopton 2009). Before DNA extraction, ethanol should be removed from samples either by evaporation at room temperature or by soaking them in Tris-EDTA buffer overnight (Bray et al. 2020). Different DNA extraction kits can be used, such as the DNeasy blood and tissue kit (Yuan et al. 2016), MasterPure Complete DNA and RNA Purification kit (Epicentre Biotechnologies) (Rueckert et al. 2011;Wakeman and Leader 2012), or PureLink genomic DNA mini kit (Invitrogen) (Clopton 2009). ...
... www.nature.com/scientificreports/ raleighana Goode & Bean and Hydrolagus mirabilis (Collett), respectively, were described based only on genetic data, because the authors considered morphology to be totally unsuitable for species characterisation 6 . To date, most of the species have been described from the North Atlantic 5-10 , whereas a few taxa have been reported from the southern seas 5,[11][12][13] , including the type species Gyrocotyle rugosa Diesing, 1850. ...
... In fact, reliable morphological identification is currently barely possible because of insufficient original descriptions dated mostly to the first half of the last century and overlapping diagnostic traits among the individual species 3,16 . Genetic identification is also limited, as sequence data are available, with one exception, for a few species from the North Atlantic, and some of them are most probably misidentified 6,[17][18][19][20] . The reliable identification of many species is thus impossible and was often based only on their host and geographic origin. ...
Gyrocotylideans are evolutionary ancient parasitic flatworms, and like their hosts—a relict group of holocephalan fishes (Chimaeriformes)—they are considered to be “living fossils” of a vanished past. However, the species diversity, host associations and biogeography of these most basal tapeworms are poorly known. Herein, we provide evidence of a conspicuous contrast between the genetic and morphological data based on an examination of newly collected and properly processed Gyrocotyle specimens (hologenophores) isolated from holocephalans off Taiwan and Argentina. Our molecular data, inferred from three genes (COI, 28S rRNA, 18S rRNA), showed unexpected genetic
interrelationships among isolates of the genus Gyrocotyle, because each of the four genotypes from Taiwan clustered with isolates of distinct gyrocotylideans from the North Atlantic. Three genotypes of Gyrocotyle from Taiwan were morphologically almost indistinguishable from each other but represented distinct genetic lineages; a single specimen of Gyrocotyle sp. genotype 4 exhibited a clear genetic and morphological distinctness, though its formal description as a new species would be premature. Additionally, specimens of Gyrocotyle rugosa Diesing, 1850, from the type host
Callorhinchus callorynchus from Argentina, provided the first genetic data on the type species of the genus and enabled us to characterise it, which is necessary for future taxonomic studies. The finding of some specimens of Gyrocotyle sp. genotype 3 in Chimaera phantasma, and another one in C. cf. argiloba, together with the putative conspecificity of an unidentified gyrocotylidean from Callorhinchus milii off Australia and G. rugosa from C. callorynchus off Argentina, represent evidence that one gyrocotylidean species may parasitize more than one holocephalan host species. Existing taxonomic problems and conflicts between morphological and molecular data on species of Gyrocotyle can only be resolved if hologenophores from type hosts and localities of nominal taxa are properly characterised genetically and morphologically.
Gyrocotylideans are evolutionary ancient parasitic flatworms, and like their hosts—a relict group of holocephalan fishes (Chimaeriformes)—they are considered to be “living fossils” of a vanished past. However, the species diversity, host associations and biogeography of these most basal tapeworms are poorly known. Herein, we provide evidence of a conspicuous contrast between the genetic and morphological data based on an examination of newly collected and properly processed Gyrocotyle specimens (hologenophores) isolated from holocephalans off Taiwan and Argentina. Our molecular data, inferred from three genes (COI, 28S rRNA, 18S rRNA), showed unexpected genetic interrelationships among isolates of the genus Gyrocotyle, because each of the four genotypes from Taiwan clustered with isolates of distinct gyrocotylideans from the North Atlantic. Three genotypes of Gyrocotyle from Taiwan were morphologically almost indistinguishable from each other but represented distinct genetic lineages; a single specimen of Gyrocotyle sp. genotype 4 exhibited a clear genetic and morphological distinctness, though its formal description as a new species would be premature. Additionally, specimens of Gyrocotyle rugosa Diesing, 1850, from the type host Callorhinchus callorynchus from Argentina, provided the first genetic data on the type species of the genus and enabled us to characterise it, which is necessary for future taxonomic studies. The finding of some specimens of Gyrocotyle sp. genotype 3 in Chimaera phantasma, and another one in C. cf. argiloba, together with the putative conspecificity of an unidentified gyrocotylidean from Callorhinchus milii off Australia and G. rugosa from C. callorynchus off Argentina, represent evidence that one gyrocotylidean species may parasitise more than one holocephalan host species. Existing taxonomic problems and conflicts between morphological and molecular data on species of Gyrocotyle can only be resolved if hologenophores from type hosts and localities of nominal taxa are properly characterised genetically and morphologically.
