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.

• Keywords
• DNA sequencing, Distribution, elasmobranchs, host associations, pathogens, phylogenetic relationships, ray-finned fish, species diversity, taxonomy,
• MeSH
• Cestoda * genetics   MeSH
• Cestode Infections * epidemiology   veterinary   MeSH
• Diphyllobothrium * MeSH
• Elasmobranchii * MeSH
• Phylogeny MeSH
• Fish Diseases * epidemiology   MeSH
• Fishes MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH

Transmission electron microscopy (TEM) was used to study the ultrastructure of the uterus and egg morphology in the enigmatic bothriocephalidean tapeworm Tetracampos ciliotheca. The uterine wall, underlain by well-developed muscle bundles, consists of a syncytial epithelium which is characterized by the abundance of free ribosomes, mitochondria and cisternae of granular endoplasmic reticulum (GER). On the apical surface of the uterine epithelium, there is an abundant network of cytoplasmic microlamellae projecting into the uterine lumen. The lumen is filled with freely lying eggs which are located close to the uterine wall but do not contact with the microlamellae of the uterine epithelium. The developed eggs possess an oncosphere surrounded by four envelopes: (1) a thin egg shell; (2) an outer envelope; (3) a syncytial, ciliated inner envelope; and (4) the oncospheral membrane. The mature hexacanth is armed with three pairs of oncospheral hooks, as well as somatic and hook muscles and five types of cells (1) binucleated subtegumental cell, (2) somatic cells, (3) penetration gland cells, (4) nerve cells and (5) germinative cells. Considering the relative scarcity of descriptive and comparative studies on the ultrastructure of the uterus and egg morphology in the order Bothriocephalidea, we concluded that Tet. ciliotheca displays a unique type of egg development. Based on these results, we discuss plausible ideas relating to the function of these structures for consideration in future studies.

• Keywords
• Bothriocephalidea, Egg, Evolution, Oncosphere, TEM,
• MeSH
• Cestoda physiology   ultrastructure   MeSH
• Cestode Infections parasitology   veterinary   MeSH
• Larva ultrastructure   MeSH
• Fish Diseases parasitology   MeSH
• Ovum ultrastructure   MeSH
• Catfishes parasitology   MeSH
• Microscopy, Electron, Transmission MeSH
• Uterus ultrastructure   MeSH
• Animals MeSH
• Check Tag
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH

Tapeworms of the genus Wenyonia Woodland, 1923 (Caryophyllidea: Caryophyllaeidae), parasites of catfishes in Africa, are revised. This revision is based on material from large-scale sampling, in the Democratic Republic of the Congo, Kenya, Senegal and the Sudan between 2006 and 2009, and the examination of all of the type-specimens available. The following six species are considered valid and their redescriptions are provided: Wenyonia virilis Woodland, 1923 (type-species; new synonym W. kainjii Ukoli, 1972); W. acuminata Woodland, 1923; W. longicauda Woodland, 1937; W. minuta Woodland, 1923 (new synonym W. mcconnelli Ukoli, 1972); W. synodontis Ukoli, 1972; and W. youdeoweii Ukoli, 1972. A key to the identification of Wenyonia spp. is provided and numerous new hosts and geographical records are reported. A comparative phylogenetic analysis of partial sequences of the 28S rRNA gene of four species divided the monophyletic genus into two lineages, one represented by W. acuminata and W. minuta and another one composed of W. virilis and W. youdeoweii.

• MeSH
• Cestoda anatomy & histology   classification   genetics   isolation & purification   MeSH
• DNA, Helminth chemistry   genetics   MeSH
• Phylogeny MeSH
• DNA, Ribosomal Spacer chemistry   genetics   MeSH
• Microscopy MeSH
• Molecular Sequence Data MeSH
• DNA, Ribosomal chemistry   genetics   MeSH
• RNA, Ribosomal, 28S genetics   MeSH
• Sequence Analysis, DNA MeSH
• Cluster Analysis MeSH
• Catfishes parasitology   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Geographicals
• Africa MeSH
• Names of Substances
• DNA, Helminth MeSH
• DNA, Ribosomal Spacer MeSH
• DNA, Ribosomal MeSH
• RNA, Ribosomal, 28S MeSH