Gyrodactylus quadratidigitus n. sp. (Monogenea: Gyrodactylidae), a parasite of the leopard-spotted goby Thorogobius ephippiatus (Lowe) from the south-western coast of the UK

The Gyrodactylus (Monogenea, Gyrodactylidae) parasite fauna of freshwater sand gobies (Teleostei, Gobioidei) in their centre of endemism, with description of seven new species

While Gobioidei comprises showcases of (adaptive) radiation, the scientific interest they yielded did not ensure full understanding of goby biodiversity. Even in a well-studied region like Europe, wide knowledge gaps remain. Sand gobies represent one of the few clades whose monogenean parasites have been thoroughly studied. However, in the Balkans, part of the sand gobies' centre of endemism, these parasites were unstudied. We focus on Greek and Croatian freshwater gobies. From five sand goby species, the first parasites are reported, describing seven new Gyrodactylus species. Economidichthys pygmaeus harbours Gyrodactylus benedeni sp. n. and Gyrodactylus dorlodoti sp. n. Its congener E. trichonis hosts G. meelkopae sp. n. Knipowitschia milleri was found to host G. charon sp. n., K. thessala is infected by G. bios sp. n., and K. croatica by G. douglasadamsi sp. n. and G. hellemansi sp. n. Gyrodactylus bubyri was found on its type host K. caucasica. A diverse parasite fauna is expected for a region known for its biodiversity and endemism. The contribution of parasites to species richness in such hotspots is overlooked. The observed species richness per host is rather low compared to the better-studied eastern Atlantic sand gobies. Host vicariance is considered to mediate parasite specificity in this fauna. Some new flatworm species display unique morphological features, such as the remarkable size of the marginal hook sickle proper compared to its foot in the Economidichthys parasites, or a characteristically kinked marginal hook sickle in G. douglasadamsi sp. n. These features reflect their hosts' endemism in the Balkans.

The biology of gyrodactylid monogeneans: the "Russian-doll killers"

This article reviews the history of gyrodactylid research focussing on the unique anatomy, behaviour, ecology and evolution of the viviparous forms while identifying gaps in our knowledge and directions for future research. We provide the first summary of research on the oviparous gyrodactylids from South American catfish, and highlight the plesiomorphic characters shared by gyrodactylids and other primitive monogeneans. Of these, the most important are the crawling, unciliated larva and the spike sensilla of the cephalic lobes. These characters allow gyrodactylids to transfer between hosts at any stage of the life cycle, without a specific transmission stage. We emphasise the importance of progenesis in shaping the evolution of the viviparous genera and discuss the relative extent of progenesis in the different genera. The validity of the familial classification is discussed and we conclude that the most significant division within the family is between the oviparous and the viviparous genera. The older divisions into Isancistrinae and Polyclithrinae should be allowed to lapse. We discuss approaches to the taxonomy of gyrodactylids, and we emphasise the importance of adequate morphological and molecular data in new descriptions. Host specificity patterns in gyrodactylids are discussed extensively and we note the importance of host shifts, revealed by molecular data, in the evolution of gyrodactylids. To date, the most closely related gyrodactylids have not been found on closely related hosts, demonstrating the importance of host shifts in their evolution. The most closely related species pair is that of G. salaris and G. thymalli, and we provide an account of the patterns of evolution taking place in different mitochondrial clades of this species complex. The host specificity of these clades is reviewed, demonstrating that, although each clade has its preferred host, there is a range of specificity to different salmonids, providing opportunities for complex patterns of survival and interbreeding in Scandinavia. At the same time, we identify trends in systematics and phylogeny relevant to the G. salaris epidemics on Atlantic salmon in Norway, which can be applied more generally to parasite epidemiology and evolution. Although much of gyrodactylid research in the last 30 years has been directed towards salmonid parasites, there is great potential in using other experimental systems, such as the gyrodactylids of poeciliids and sticklebacks. We also highlight the role of glacial lakes and modified river systems during the ice ages in gyrodactylid speciation, and suggest that salmon infecting clades of G. salaris first arose from G. thymalli in such lakes, but failed to spread fully across Scandinavia before further dispersal was ended by rising sea levels. This dispersal has been continued by human activity, leading to the appearance of G. salaris as a pathogen in Norway. We review the history and current status of the epidemic, and current strategies for elimination of the parasite from Norway. Finally, we consider opportunities for further spread of the parasite within and beyond Europe.

Four new species of Gyrodactylus von Nordmann, 1832 (Monogenea, Gyrodactylidae) on gobiid fishes: combined DNA and morphological analyses

Four Gyrodactylus species parasitising four closely related gobiid species in European coastal waters were studied and compared with G. arcuatus Bychowsky sensu Bychowsky & Poljansky (1953) from Gasterosteus aculatus . These were G. gondae n. sp. from Pomatoschistus minutus and P. lozanoi , G. flavescensis n. sp. from Gobiusculus flavescens , G. arcuatoides n. sp. from P. minutus and G. branchialis n. sp. from P. microps. Combined molecular and morphological analyses, as well as morphometric and statistical methods, were used. The ssrRNA V4 region and the complete ITS rDNA region were sequenced. Genetically the four new species are clearly distinct from G. arcuatus . From a morphological point of view, the haptoral hard parts of G. gondae n. sp., G. flavescensis n. sp. and G. arcuatoides n. sp. are related to those of G. arcuatus, while these parts of G. branchialis n. sp. are different, but related to those of G. quadratidigitus Longshaw, Pursglove & Shinn, 2003. For the latter two species, a new species group is formed. The V4 and ITS sequence analyses, however, indicate a close relationship between G. branchialis and the three G. arcuatus-like species.

Molecular and morphological comparisons between Gyrodactylus ostendicus n. sp. (Monogenea: Gyrodactylidae) on Pomatoschistus microps (Krøyer) and G. harengi Malmberg, 1957 on Clupea harengus membras L

Gyrodactylus ostendicus n. sp. was exclusively found on fins of the common goby Pomatoschistus microps (Krøyer). The haptoral hard parts are among the smallest described for species of Gyrodactylus. A presumed similarity between the new species and G. harengi Malmberg, 1957 (subgenus Metanephrotus Malmberg, 1964) encouraged a comparative approach. A morphological analysis showed the marginal hook sickles of G. ostendicus to be of quite a different type and similar to those of G. arcuatus Bychowsky sensu Bychowsky & Poljansky (1953) (subgenus Mesonephrotus Malmberg, 1964). The new species has a pharynx with short pharyngeal processes. Its protonephridial system has small bladders, indicating an association with the subgenera Mesonephrotus or Metanephrotus. Molecular phylogenetic analyses, including all of the species of Mesonephrotus and Metanephrotus currently available on the GenBank database, suggested that the new species belongs to Mesonephrotus. Combined morphological and molecular studies of the new species show that G. ostendicus is more closely related to G. arcuatus than to G. harengi.