First adult cyclophyllidean tapeworm (Cestoda) from teleost fishes: host switching beyond tetrapods in Africa

Manual for the study of tapeworms (Cestoda) parasitic in ray-finned fish, amphibians and reptiles

Based on long-term and often frustrating experiences with the poor quality of tapeworms (Cestoda) collected throughout the world for taxonomic and phylogenetic studies, and considering the increasing obstacles to obtaining new material, a simple, easy-to-use and illustrated methodological guide (manual) is provided. It focusses mainly on key steps in examining hosts, collecting cestodes from poikilothermous vertebrates except elasmobranchs, i.e., from ray-finned fish (Actinopterygii), amphibians and 'reptiles' (a paraphyletic group comprising all sauropsids except birds), and fixing them for subsequent morphological and molecular study. It is proposed that the following methodological points should be followed: (i) ideally only freshly euthanised hosts (not previously frozen) should be used for parasitological examination; (ii) hosts examined should be documented by photographs; host tissue should also be preserved for future genotyping if necessary; (iii) tapeworms should be detached carefully to keep the scolex intact and properly cleaned before fixation; (iv) a small piece of cestode tissue should be always preserved in molecular grade ethanol for DNA sequencing; (v) tapeworms should be fixed as quickly as possible after collecting them and while they are still alive, always using hot (heated) fixatives; this prevents unnatural contraction or deformation and ensures uniform fixation; (vi) each sample (vial) should be properly labelled (a unique code should be given to every cestode sample); (vii) vouchers of sequenced specimens (hologenophores or paragenophores) should always be preserved for identification, and deposited in internationally recognised collections. It is hoped that this guide helps researchers and students to properly process valuable material of cestodes to make it suitable for reliable identification including genotyping and comparative anatomy, which is a prerequisite for any subsequent ecological, biogeographical, phylogenetic life cycle or molecular study.

Fish tapeworms (Cestoda) in the molecular era: achievements, gaps and prospects

The tapeworms of fishes (Chondrichthyes and Actinopterygii) account one-third (1670 from around 5000) of the total tapeworm (Platyhelminthes: Cestoda) species diversity. In total 1186 species from 9 orders occur as adults in elasmobranchs (sharks, rays and chimaeras), and 484 species from 8 orders mature in ray-finned fishes (referred to here as teleosts). Teleost tapeworms are dominated by freshwater species (78%), but only 3% of elasmobranch tapeworms are known from freshwater rays of South America and Asia (Borneo). In the last 2 decades, vast progress has been made in understanding species diversity, host associations and interrelationships among fish tapeworms. In total, 172 new species have been described since 2017 (149 from elasmobranchs and 23 from teleosts; invalidly described taxa are not included, especially those from the Oriental region). Molecular data, however, largely limited to a few molecular markers (mainly 28S rDNA, but also 18S and cox1), are available for about 40% of fish tapeworm species. They allowed us to significantly improve our understanding of their interrelationships, including proposals of a new, more natural classification at the higher-taxonomy level (orders and families) as well as at the lower-taxonomy level (genera). In this review, we summarize the main advances and provide perspectives for future research.