o:2060 An ancient alliance: Matching evolutionary patterns of cartilaginous fishes (Elasmobranchii) and chloromyxid parasites (Myxozoa) en Myxozoa is a group of endoparasitic cnidarians covering almost 2600 species but merely 53 species, mostly from the genus Chloromyxum, have been reported from sharks, rays, and skates (Elasmobranchii). Elasmobranchs play a key role in the study of evolutionary trajectories of myxozoans as they represent ancestral vertebrate hosts. Our study provides new data on Chloromyxum spp. from 57 elasmobranchs, covering 20 species from geographical regions and host groups not previously investigated, such as Lamniformes and Hexanchiformes, the most basal phylogenetic shark lineage. In total, 28% of elasmobranchs were infected with Chloromyxum spp., indicating high diversity. Of the seven distinguished species, six are formally described based on morphological, morphometric, and genetic (18S rDNA) data. Comprehensive co-phylogenetic analyses and ancestral state reconstruction revealed that parasite and host phylogenies are clearly correlated, resulting in a distinct phylogenetic separation of chloromyxids from selachid (shark) vs. batoid (ray and skate) hosts. Species infecting the most ancient elasmobranchs formed a sublineage, branching off in the middle of the Chloromyxum sensu stricto clade. Our findings indicate that chloromyxids likely invaded an ancestral elasmobranch prior the time of divergence of shark and batoid lineages. Our analyses did not show a clear phylogeographic pattern of Chloromyxum parasites, probably due to the cosmopolitan distribution and migratory behaviour of many elasmobranch hosts, but geographical sampling must be extended to confirm or refute this observation. This study provides a complex view on species diversity, phylogeny, evolution, host-parasite co-phylogeny, and the phylogeographic origin of Chloromyxum species from elasmobranchs. Our results highlight the importance of adding missing data from previously un- or undersampled geographical regions and host species which results in a more accurate estimate of myxozoan biodiversity and a better understanding of the evolution of this parasite group in their hosts and in the different oceans of our planet. Animals; Elasmobranchiigeneticsparasitology; Fishesparasitology; Myxozoagenetics; Parasites; Phylogeny 1552099 10.1016/j.meegid.2022.105346 2023-09-05T08:25:05.988Z 44 yes 46 Martina Lisnerová Czech Academy of Sciences / University of South Bohemia Inga Nicole Martinek Czech Academy of Sciences / Swedish Museum of Natural History Stockholm person Gema Alama-Bermejo Czech Academy of Sciences / Centro de Investigación Aplicada y Transferencia Tecnológica en Recursos Marinos Almirante Storni (CIMAS) CCT CONICET - CENPAT / University of Veterinary Medicine Vienna person Kateřina Bouberlová University of South Bohemia person Bjoern C. Schaeffner University of Iceland Reykjavík person Nomfundo Nkabi KwaZulu-Natal Sharks Board Umhlanga Rocks person Astrid S. Holzer Czech Academy of Sciences / University of Veterinary Medicine Vienna person 0000-0002-4916-3172 Pavla Bartošová-Sojková Czech Academy of Sciences person application/pdf 7723577 https://phaidra.vetmeduni.ac.at/o:2060 no yes 16 70 1552253 Infection Genetics and Evolution 14 103 Elsevier 2022