Consistent Negative Correlations between Parasite Infection and Host Body Condition Across Seasons Suggest Potential Harmful Impacts of Salmincola markewitschi on Wild White-Spotted Charr, Salvelinus leucomaenis.

Assessing the impacts of parasites on wild fish populations is a fundamental and challenging aspect of the study of host-parasite relationships. Salmincola, a genus of ectoparasitic copepods, mainly infects salmonid species. This genus, which is notorious in aquaculture, damages host fishes, but its impacts under natural conditions remain largely unknown or are often considered negligible. In this study, we investigated the potential impacts of mouth-attaching Salmincola markewitschi on white-spotted charr (Salvelinus leucomaenis) through intensive field surveys across four seasons using host body condition as an indicator of harmful effects. The prevalence and parasite abundance were highest in winter and gradually decreased in summer and autumn, which might be due to host breeding and/or wintering aggregations that help parasite transmissions. Despite seasonal differences in prevalence and parasite abundance, consistent negative correlations between parasite abundance and host body condition were observed across all seasons, indicating that the mouth-attaching copepods could reduce the body condition of the host fish. This provides field evidence suggesting that S. markewitschi has a potential negative impact on wild white-spotted charr.

Ceratocolax tavaresi n. sp. (Copepoda: Bomolochidae) parasitic in the Tomtate Grunt Haemulon aurolineatum Cuvier, 1830 (Actinopterygii: Haemulidae) off Rio de Janeiro, southeastern Brazil.

PURPOSE: A new species of the genus Ceratocolax Vervoort, 1965 is described based on specimens collected from the Tomtate grunt Haemulon aurolineatum Cuvier, caught in the coast of Angra dos Reis, off the State of Rio de Janeiro, Brazil. METHODS: One hundred specimens of H. aurolineatum were purchased from the local fish market and examined for parasitic copepods. Parasites were fixed and preserved in 80% ethanol. Morphological features of the copepods were examined and drawn using an Olympus BX51 equipped with a drawing tube. RESULTS: Ceratocolax tavaresi n. sp. can be distinguished from all congeners by the following combination of characters in the adult female: (1) second endopodal segment of leg 3 with one seta, (2) lack of stout spinules along outer margins on rami of legs 2-4, (3) genital somite without flaplike structures, (4) terminal exopodal segment of leg 4 with seven elements; and in the adult male: (1) legs 1 to 4 with 3-segmented rami (except endopod of leg 4), (2) presence of a pair of blunt processes on dorsal surface of the third pedigerous somite, (3) second endopodal segment of leg 3 with one seta. CONCLUSION: The number of species of Ceratocolax reported in the Atlantic Ocean was increased to three, including the new species. This is the forty-second species of copepod found parasitizing haemulid fish in marine waters from the Americas; however, the diversity of parasitic copepods off this continent is still underestimated.

Salmincola markewitschi or S. carpionis (Copepoda: Lernaeopodidae)? A requirement for taxonomic revision due to their high morphological variations.

Salmincola markewitschi Shedko et Shedko, 2002 (Copepoda: Lernaeopodidae) is an ectoparasitic copepod mainly infecting the buccal cavities of white-spotted charr Salvelinus leucomaenis (Pallas) (Salmonidae). This species has only been recorded from Northeast Asia, where a morphologically similar congener Salmincola carpionis (Krøyer, 1837) is also distributed, using the same host species. These copepods are hard to distinguish from each other because of their similarities. We thus examined the newly collected specimens morphologically and genetically from five populations of white-spotted charr in Japan. Most of the specimens were morphologically consistent with S. markewitschi but showed great variations in the numbers of spines on the exopods of the antennae, shape of the maxilliped myxal palps, and the bulla diameter. Consequently, some specimens shared characteristics with S. carpionis. In addition to the mophological continuities, genetic analyses of 28S rDNA and COI mitochondrial DNA confirmed that all specimens belong to a single species. Further taxonomic revisions are required to draw conclusions of whether S. markewitschi is a valid species different from S. carpionis, by collecting samples from across their wide distributional ranges, such as Europe, North America, and Northeast Asia. A key to identification of species of Salmincola Wilson, 1915 occurring in Japan is also provided.

A New Species of Hatschekiid Copepod (Crustacea: Hatschekiidae) Parasitic on the Porkfish Anisotremus virginicus (Linnaeus, 1758) (Actinopterygii: Haemulidae), with Notes on Previously Known Species of Hatschekia Poche, 1902 Collected from Actinopterygians off Brazil.

INTRODUCTION: Copepods of the genus Hatschekia Poche, 1902 are parasitic on the gills of marine actinopterygians. Currently, about 151 species of this genus have been reported in marine ecosystems and only few occur in South Atlantic Ocean. METHODS: Fifty specimens of A. virginicus from Angra dos Reis, off the State of Rio de Janeiro, Brazil, were parasitized by copepods on the gills. Parasites were fixed and preserved in 70% ethanol. Morphological observations were based on light and scanning electron microscopy. RESULTS: Hatschekia nagasawai n. sp. can be distinguished from all congeners by the combination of the following characters: (1) presence of two pointed processes on the proximal (first) segment of antennule, (2) cephalothorax octagonal to ovoid, (3) absence of processes on the intercoxal sclerite of legs 1 and 2, (4) trunk without lobes at the postero-lateral margins. Other species of Hatschekia and their hosts previously collected off Brazil were analysed and discussed. CONCLUSIONS: This is the first report of a representative of the family Hatschekiidae Kabata, 1979 parasitizing a species of Anisotremus. The number of species of Hatschekia reported in the South Atlantic Ocean was increased to five, including the new species; however, the diversity of hatschekiid copepods in this oceanographic region is still underestimated, most likely being higher than what is currently known.

Host specificity and the reproductive strategies of parasites.

Environmental stability can have profound impacts on life history trait evolution in organisms, especially with respect to development and reproduction. In theory, free-living species, when subjected to relatively stable and predictable conditions over many generations, should evolve narrow niche breadths and become more specialized. In parasitic organisms, this level of specialization is reflected by their host specificity. Here, we tested how host specificity impacts the reproductive strategies of parasites, a subject seldomly addressed for this group. Through an extensive review of the literature, we collated a worldwide dataset to predict, through Bayesian multilevel modelling, the effect of host specificity on the reproductive strategies of parasitic copepods of fishes or corals. We found that copepods of fishes with low host specificity (generalists) invest more into reproductive output with larger clutch sizes, whereas generalist copepods of corals invest less into reproductive output with smaller clutch sizes. The differences in host turnover rates through an evolutionary timescale could explain the contrasting strategies across species observed here, which should still favour the odds of parasites encountering and infecting a host. Ultimately, the differences found in this study reflect the unique evolutionary history that parasites share both intrinsically and extrinsically with their hosts.

Microhabitat use of Pseudocharopinus markewitschi (Gusev, 1951) (Copepoda: Lernaeopodidae) on the mottled skate, Beringraja pulchra (Liu, 1932): Does biased occurrence on the dorsal side of the pelvic fin imply a safety zone?

The mottled skate Beringraja pulchra is a coastal fish caught by gillnet and bottom trawl fisheries in Hokkaido, Japan. We recently found a parasitic copepod identical to Pseudocharopinus markewitschi (Gusev, 1951) on this commercially important fish. A total of 109 host individuals caught off the coast of northern Hokkaido, Japan, were examined for adult females of this copepod, and 67 cases (61.5%) of infection comprised with 31 cases (67.4%) of 46 males and 36 cases (57.1%) of 63 females were found. The parasite specimens (n = 229) were recovered mainly from the dorsal side of the pelvic fin (n = 168, 73.4%), followed by the claspers (n = 32, 14.0%). The mottled skate is thought to spend most of its lifetime lying in sand or crawling on the seafloor. Therefore, the biased infection to the dorsal side of the pelvic fin may imply that site selection favors less susceptible for disturbances resulting from such host-specific behavior.

Ceratosomicola oki n. sp., a New Species of Copepod (Cyclopoida: Splanchnotrophidae) Parasitic on the Chromodoridid Nudibranch Glossodoris misakinosibogae Baba, 1988 Off the Oki Islands, Japan, with Microanatomical Observation Using Micro-CT.

A new species of the family Splanchnotrophidae Norman and Scott, 1906 (Cyclopoida) is described based on both sexes collected from off the Oki Islands, the Sea of Japan. Specimens of both sexes of Ceratosomicola oki n. sp. were found in the body cavities of Glossodoris misakinosibogae Baba, 1988 (Nudibranchia: Chromodorididae). The copepod is characterized by the following female characters: the cephalosome with a pair of dorsolateral horn-like processes; the prosome with hemispherical posterolateral lobes on the middle region. Non-destructive, micro-computed tomography (micro-CT) imaging performed on a single specimen of the nudibranch revealed a heavy infection by a total 17 specimens of C. oki n. sp. Almost all individuals of the copepod were attached on the surface of the middle to posterior parts of the visceral sac, forming a dense cluster. The four females bearing developed lateral processes on the prosome faced the anterior end of the visceral sac and positioned the posterior tip of the body under the secondary gills of the host. The males fitted in the gaps between the females' bodies. Further, the distribution and shape of the reproductive organs of both sexes were partially clarified by micro-CT imaging.

Potential negative effects and heterogeneous distribution of a parasitic copepod Salmincola edwardsii (Copepoda: Lernaeopodidae) on Southern Asian Dolly Varden Salvelinus curilus in Hokkaido, Japan.

The genus Salmincola is an ectoparasitic copepod group commonly infesting the branchial and buccal cavities of salmonids. While negative impacts on hatchery fishes have been reported, their impacts on wild fish populations and distribution patterns are critically understudied. In the Shiretoko Peninsula, Hokkaido, Japan, we found parasites belonging to this genus on the branchial cavity of a stream salmonid, Southern Asian Dolly Varden Salvelinus curilus. All parasites recovered were identified as Salmincola edwardsii based on morphological characteristics and partial 28S rDNA sequences. Prevalence was highly heterogeneous even among neighboring streams (0-54.8%, < 10 km) with the mean intensity among streams being generally low (2.19 parasites/infeted fish). Despite the low intensity, quantile regression analysis showed negative trends between parasite intensity and host condition, suggesting that the infestation of S. edwardsii has a potential negative impact on the host salmonid. In addition, a single copepod was found from an anadromous fish, which could indicate some salinity tolerance of the copepods. It is important to evaluate the effects of Salmincola spp. on host species and determine the limiting factors on the parasite's distribution for proper management.

Marine vampires: Persistent, internal associations between bacteria and blood-feeding marine annelids and crustaceans.

Persistent bacterial presence is believed to play an important role in host adaptation to specific niches that would otherwise be unavailable, including the exclusive consumption of blood by invertebrate parasites. Nearly all blood-feeding animals examined so far host internal bacterial symbionts that aid in some essential aspect of their nutrition. Obligate blood-feeding (OBF) invertebrates exist in the oceans, yet symbiotic associations between them and beneficial bacteria have not yet been explored. This study describes the microbiome of 6 phylogenetically-diverse species of marine obligate blood-feeders, including leeches (both fish and elasmobranch specialists; e.g., Pterobdella, Ostreobdella, and Branchellion), isopods (e.g., Elthusa and Nerocila), and a copepod (e.g., Lernanthropus). Amplicon sequencing analysis revealed the blood-feeding invertebrate microbiomes to be low in diversity, compared to host fish skin surfaces, seawater, and non-blood-feeding relatives, and dominated by only a few bacterial genera, including Vibrio (100% prevalence and comprising 39%-81% of the average total recovered 16S rRNA gene sequences per OBF taxa). Vibrio cells were localized to the digestive lumen in and among the blood meal for all taxa examined via fluorescence microscopy. For Elthusa and Branchellion, Vibrio cells also appeared intracellularly within possible hemocytes, suggesting an interaction with the immune system. Additionally, Vibrio cultivated from four of the obligate blood-feeding marine taxa matched the dominant amplicons recovered, and all but one was able to effectively lyse vertebrate blood cells. Bacteria from 2 additional phyla and 3 families were also regularly recovered, albeit in much lower abundances, including members of the Oceanospirillaceae, Flavobacteriacea, Porticoccaceae, and unidentified members of the gamma-and betaproteobacteria, depending on the invertebrate host. For the leech Pterobdella, the Oceanospirillaceae were also detected in the esophageal diverticula. For two crustacean taxa, Elthusa and Lernanthropus, the microbial communities associated with brooded eggs were very similar to the adults, indicating possible direct transmission. Virtually nothing is known about the influence of internal bacteria on the success of marine blood-feeders, but this evidence suggests their regular presence in marine parasites from several prominent groups.

Choniomyzon taiwanensis n. sp. (Crustacea: Copepoda: Nicothoidae) Parasitic on the External Egg Mass of the Longlegged Spiny Lobster Panulirus longipes longipes (Crustacea: Decapoda: Palinuridae) from Taiwanese Waters.

Choniomyzon taiwanensis n. sp. is described based on specimens collected from examining external egg masses of spiny lobster Panulirus longipes longipes (Milne-Edwards, 1868), obtained from Hualien, Taiwan. The new species differs from its congeners in possessing the following characteristics: (1) small prosome (about 0.84 mm); (2) armature of antennule being 1, 1, 2, 2, 1, 1, 1, 2, 1, 1+1 (aesthetasc), 4, 6+1 (aesthetasc); (3) five-segmented antenna; (4) second segment of antenna bearing 1 inner seta; (5) two-segmented maxilla. Based on the evidence of distinctive morphological features and host preference, Choniomyzon taiwanensis n. sp. is a new species. Until now, four species of Choniomyzon have been known living on decapods, and the new species reported here is the first record of Choniomyzon species from spiny lobster in Taiwanese waters.

Parasitic copepod (Lernanthropus kroyeri) on caged sea bass (Dicentrarchus labrax): An estimation of abundance and internal infestation pressure.

Infestation by parasitic copepods is a substantial problem in the cage culture of European sea bass (Dicentrarchus labrax). The Copepoda parasite, Lernanthropus kroyeri (Lernanthropidae), is one of the threats to the mariculture of sea bass. In the present study, we evaluated the data of abundance for L. kroyeri pre-adults and adult males (PAAM) and ovigerous adult females (AFo ) to estimate the internal infection pressure (IIP) in the same cage environment. The sea bass infested by L. kroyeri was collected from grow-out sea cages located in Gulluk Bay (Turkey) in September and October 2019. Mean fish weight and length of sea bass were 75.79 ± 1.66 g and 21.40 ± 0.56 cm, respectively. The fixed lag method was used to predict the abundance of L. kroyeri adult females. The overall prevalence of L. kroyeri was 60%. The mean abundance of PAAM and AFo varied from 0.8 ± 0.24 to 2.5 ± 0.67 and 2.9 ± 0.40 to 4.3 ± 0.55, respectively. The abundance of AF was strongly correlated with PAAM. The pattern of AFo and PAAM was interpreted as an indication of the continuous infestation of L. kroyeri on sea bass. Our results showed that the correlation of AFo abundance for five consecutive weeks was significant, representing the main determinative factor for the continuity of the parasitic load. In our approach, internal infestation pressure is the quantitative estimation of the potential infective copepodids, which are mainly characterized by AF abundance and the prevalence. We predicted that the internal infestation pressure could be high, even exceeding the 50.000 × 106 potential infective copepodids for one sea cage with the fish density of 20 sea bass/m3 .

Larval parasitic copepods affect early life history traits of a temperate clingfish.

Larval copepods are frequent parasites that infest fish larvae along the Chilean coast. Because these parasites develop on fish during the early development, when their bodies are fragile and in a recent stage, they can affect the fishes' early life history traits (ELHT). The goal of this study was to determine the effect of parasitic copepods on the ELHT of the larvae of the clingfish Gobiesox marmoratus (Teleostei: Gobiesocidae) using otolith microstructure analysis. Ichthyoplankton samples were collected during austral winter (July and August 2012), in the inner shelf waters off Valparaiso Bay, central Chile. A total of 95 non-parasitized larvae (NPL) and 95 parasitized (PL) with copepods were randomly selected for subsequent analyses. Parasitized larvae of G. marmoratus were larger than NPL. The right otolith tended to be larger than the left otolith in the fish larvae, but with a higher asymmetry in PL. The PL showed larger otoliths-at-size than the NPL, particularly in smaller larvae (< 8 mm of standard length, SL). Nonetheless, parasitized larvae larger than 8 mm SL showed the opposite trend that is smaller-at-size otoliths than NPL. The Gompertz models indicated that the asymptotic length of NPL doubled the length of PL; this suggests that parasitic copepods affect the maximum size attained by the PL. In conclusion, parasitic copepods negatively affect the ELHT of G. marmoratus larvae and the greater asymmetry can be attributed to parasitism.

The discovery of Caligus quadratus Shiino, 1954 (Copepoda: Caligidae) in the Mediterranean Sea, with a new host record and supplementary morphological information obtained using confocal laser scanning microscope (CLSM) and 3D image processing.

In this study, supplementary information on the morphology of the siphonostomatoid copepod Caligus quadratus Shiino, 1954 (Copepoda: Caligidae) is given based on the new material collected from the gills of the Atlantic bluefin tuna, Thunnus thynnus (Linnaeus, 1758) caught in the Gulf of Antalya, Turkey. The morphology of C. quadratus is re-examined for the first time by adopting a recently developed visualisation technique by Kamanli et al. [1]. Appendages of Congo red stained specimens of C. quadratus were dissected and scanned using confocal laser scanning microscope (CLSM) and the CLSM images were processed using Dristhi software programme. 3D reconstructions of some confusing appendages were visualised using Drishti. Line drawing was used to depict the habitus of both female and male C. quadratus. Key diagnostic characters of C. quadratus are presented together with the newly observed additional taxonomic characters. In addition, previously misinterpreted and simply overlooked features in the previous descriptions of C. quadratus are also re-described. This is the first report of C. quadratus from the Mediterranean Sea and the Atlantic bluefin tuna constitutes a new host record for this caligid copepod.

Mesoparasitic copepods (Copepoda: Cyclopoida) associated with polychaete worms in European seas.

A large collection of mesoparasitic copepods from polychaete hosts collected in northern European waters was examined. The term mesoparasitic refers to highly transformed copepods where the adult female attaches by embedding part of its body in the host. Representatives of five known familes were found and a new family is established. A single new species, Bradophila minuta sp. nov., was described in the family Bradophilidae. It occurred exclusively on the flabelligerid Diplocirus glaucus (Malmgren, 1867). Two genera of the family Herpyllobiidae were represented: Herpyllobius Steenstrup Lütken, 1861 and Eurysilenium M. Sars, 1870. Herpyllobius arcticus Steenstrup Lütken, 1861 was found on at least five different polynoid hosts, two of which, Harmothoe fragilis Moore, 1910 and Antinoe sp., were new host records. A new species, H. cluthensis sp. nov. was described from Malmgrenia species in Scottish waters. The large species, Herpyllobius cordiformis Lützen, 1964, was collected in Arctic waters from Eunoe cf. oerstedi. It is the first report of this parasite in Europe. The common parasite H. polynoes (Krøyer, 1864) was found on six different polynoid hosts, three of which, Harmothoe bifera, Malmgreniella mcintoshi Tebble Chambers, 1982 and Eunoe ?barbata are new host records. Eurysilenium truncatum M. Sars, 1870 was collected from Eucranta villosa Malmgren, 1866, Eunone sp., and Gattyana cirrhosa (Pallas, 1766). The material from Eucranta villosa caught at 72.6ºN comprises both a new host record and is the most northerly report of this parasite. Specimens of Eurysilenium which differed from E. truncatum in a number of features were found on Harmothoe fragilis and H. impar (Johnston, 1839). A new family, the Pholoicolidae, is established to accommodate Pholicola chambersae gen. et sp. nov., parasitic on Pholoe pallida Chambers, 1985. The family Phyllodicolidae was represented by all three of its known species: Phyllodicola petiti (Delamare Deboutteville Laubier, 1960), Cyclorhiza eteonicola Heegaard, 1942 and C. megalova Gotto Leahy, 1988. The former was found on Eumida ockelmanni Eibye-Jacobsen, 1987, a new host record. A single ovigerous female of C. eteonicola was collected from a new host, Eteone spetsbergensis Malmgren, 1865. Cyclorhiza megalova was common on Eteone longa (Fabricius, 1780) and E. longa/flava complex. A rich diversity of members of the family Saccopsidae was found, including three known species of Melinnacheres M. Sars, 1870 plus nine new species placed in four new genera. Melinnacheres was represented by M. ergasiloides M. Sars, 1870, M. steenstrupi Bresciani Lützen, 1961 and M. terebellidis Levinsen, 1878. Melinnacheres ergasiloides was found on Melinna elizabethae McIntosh, 1914, M. steenstrupi on members of the Terebellides stroemi-complex and T. atlantis Williams, 1984, while M. terebellidis was found on the T. stroemi-complex and on T. shetlandica Parapar, Moreira O'Reilly, 2016. A new genus, Trichobranchicola gen. nov., was established to accommodate T. antennatus gen. et sp. nov., a parasite of Trichobranchus sikorskii Leontovich Jirkov in Jirkov, 2001, T. glacialis Malmgren, 1866 and Trichobranchus sp. The second new genus, Lanassicola gen. nov., was established to accommodate the type species, Lanassicola arcticus gen. et sp. nov. parasitic on Lanassa venusta (Malm, 1874), plus two additional species, L. bilobatus gen. et sp. nov. on Lanassa nordenskjoeldi Malmgren, 1866, and L. dorsilobatus gen. et sp. nov. on Proclea graffii (Langerhans, 1884). A new subfamily, Euchonicolinae, was established within the Saccopsidae to accommodate two new genera, Euchonicola gen. nov. and Euchonicoloides gen. nov. The type species of Euchonicola gen. nov. is E. caudatus gen. et sp. nov., a parasite of Euchone sp., and it includes two other species, E. linearis gen. et sp. nov. on Chone sp., and E. parvus gen. et sp. nov. on Euchone sp. The type species of Euchonicoloides gen. nov. is E. elongatus gen. et sp. nov. found on a host belonging to the genus Euchone, and it also includes Euchonicoloides halli gen. et sp. nov. from Jasmineira caudata Langerhans, 1880. Four species of the family Xenocoelomidae were found: Xenocoeloma alleni (Brumpt, 1897), X. brumpti Caullery Mesnil, 1915, X. orbicularis sp. nov. and Aphanodomus terebellae (Levinsen, 1878). Xenocoeloma alleni was found on four different species of Polycirrus and on Amaeana trilobata (M. Sars, 1863) and X. brumpti was found on Polycirrus norvegicus Wollebaek, 1912. Xenocoeloma orbicularis sp. nov. occurred only on Paramphitrite birulai (Ssolowiew, 1899). Aphanodomus terebellae was found on three hosts, only one of which, Leaena abranchiata was new.

Redescription of Lernaeenicus stromatei Gnanamuthu, 1953 (Copepoda: Siphonostomatoida: Pennellidae) infesting the Black Pomfret Parastromateus niger (Bloch) from Indian waters.

The parasitic copepod Lernaeenicus stromatei Gnanamuthu, 1953 infecting black pomfret, Parastromateus niger (Bloch) (Carangidae) is redescribed based on a neotype and additional fresh material obtained from hosts collected at different fish landing centers on the Chennai Coast (Tamil Nadu), Malabar Coast (Kerala), and from West Bengal, India. A female L. stromatei obtained from the Chennai Coast has been designated as a neotype and deposited in the National Zoological Collections of Zoological Survey of India (NZC-ZSI). Lernaeenicus stromatei can be identified based on the following features: A long and slender body; head anteriorly rounded, dorso-ventrally flattened and slightly longer than broad; presence of three posterior horns on the head, one median and two lateral, all sub-similar and apically rounded; and an anterior neck with an indistinct partition on the dorsal side, indicating thoracic segments, and a three-jointed antennule.

The discovery of Lepeophtheirus acutus Heegaard, 1943 (Copepoda: Caligidae) from two new elasmobranch hosts in the Mediterranean Sea, and a comparative redescription of Lepeophtheirus rhinobati Luque, Chaves et Cezar, 1998.

In this study, supplementary information on the morphology of the siphonostomatoid copepod Lepeophtheirus acutus Heller, 1865 is given based on new material collected from the ventral body surface and mouth cavity of common guitarfish, Rhinobatos rhinobatos (Linnaeus) and from the branchial cavity of bull ray, Aetomylaeus bovinus (Geoffroy Saint-Hilaire) caught in Iskenderun Bay, Turkey. This is the first report of L. acutus from Mediterranean waters. Key diagnostic characters of both sexes are reported, supported by light and scanning electron microscopy observations. In addition, Lepeophtheirus rhinobati Luque, Chaves et Cezar, 1998, which is closely related to L. acutus and has been reported from the same host genus, Rhinobatos, is reexamined based on paratypes stored in the collections of the United States National Museum of Natural History. Some of the key diagnostic characters which were incompletely known or lacking in the original description of both sexes of L. rhinobati are redescribed and/or presented for the first time.

Biological invasions and host-parasite coevolution: different coevolutionary trajectories along separate parasite invasion fronts.

Host-parasite coevolution has rarely been observed in natural systems. Its study often relies on microparasitic infections introducing a potential bias in the estimation of the evolutionary change of host and parasite traits. Using biological invasions as a tool to study host-parasite coevolution in nature can overcome these biases. We demonstrate this with a cross-infection experiment in the invasive macroparasite Mytilicola intestinalis and its bivalve host, the blue mussel Mytilus edulis. The invasion history of the parasite is well known for the southeastern North Sea and is characterised by two separate invasion fronts that reached opposite ends of the Wadden Sea (i.e. Texel, The Netherlands and Sylt, Germany) in a similar time frame. The species' natural history thus makes this invasion an ideal natural experiment to study host-parasite coevolution in nature. We infected hosts from Texel, Sylt and Kiel (Baltic Sea, where the parasite is absent) with parasites from Texel and Sylt, to form sympatric, allopatric and naïve infestation combinations, respectively. We measured infection rate, host condition and parasite growth to show that sympatric host-parasite combinations diverged in terms of pre- and post-infection traits within <100 generations since their introduction. Texel parasites were more infective and more efficient at exploiting the host's resources. Hosts on Texel, on the other hand, evolved resistance to infection, whereas hosts on Sylt may have evolved tolerance. This illustrates that different coevolutionary trajectories can evolve along separate invasion fronts of the parasite, highlighting the use of biological invasions in studies of host-parasite coevolution in nature.

The external morphology of adult female Egrasilus labracis as shown using hexamethyldisilazane treated, uncoated specimens for scanning electron microscopy.

The description and application of a modified Scanning Electron Microscope preparation technique using hexamethyldisilazane for small parasitic copepods was demonstrated though a high resolution depiction of individuals of Ergasilus labracis sampled from three spined stickleback (Gasterosteus aculeatus) in Bay D'Espoir, Newfoundland during summer 2015 and from archival samples retrieved from Atlantic salmon par (Salmo salar) stored at the Atlantic reference centre, St. Andrews, New Brunswick. The specimens were very well preserved showing high quality detail of important features and verifying those previously described using light microscopy by Hogans. Additionally the technique allowed excellent in situ demonstrations of mouth parts, swimming legs, and unusual and previously undescribed features of the second antenna including prominent striations and pore-like structures found to define the claw. It is thought that this technique will become a quick and efficient tool for describing important taxonomic features of small parasitic copepods like E. labracis or other similar small aquatic organisms. Microsc. Res. Tech. 79:657-663, 2016. © 2016 Wiley Periodicals, Inc.

Euryphorus brachypterus (Copepoda: Caligidae) on wild pacific bluefin tuna from the Tsugaru Strait, northern Japan.

Parasitic copepods infecting large scombrid fishes have been known for a long time because their hosts are economically important. Most studies, however, have focused on their morphology or their infection status in aquaculture from pathological viewpoints, and very few quantitative surveys have been conducted under conditions in the wild. This study therefore investigated the prevalence of Euryphorus brachypterus (Caligidae) in wild Pacific bluefin tuna (PBF). Results of sampling from August to September 2014 at the western area of the Tsugaru Strait, Japan showed that 13.2% of the PBF individuals (n = 1978) were infected with this copepod. The prevalence of infections was highest in larger fish but varied among landing dates, which were classified into three clusters and in all smaller fish, the prevalence of infections was zero. This suggests that E. brachypterus mainly uses the larger PBF, which becomes sources of further infections in other seas, and that at least two host populations with different infection statuses at the strait.

Detailed surface morphology of the 'lobster louse' copepod, Nicothoë astaci, a haematophagous gill parasite of the European lobster, Homarus gammarus.

The ectoparasitic copepod, Nicothoë astaci (the 'lobster louse'), infests the gills of the European lobster, Homarus gammarus. There have been limited studies on this haematophagous species; therefore knowledge of this parasite is rudimentary. The current study examines the surface morphology of this parasitic copepod, detached from the host, concentrating on adaptations of the suctorial mouthpart, the oral disc. Cryo-scanning electron microscopy revealed structural adaptations that facilitate attachment of these parasites to the gill filaments of their lobster host. The aperture of the feeding channel, through which host haemolymph is drawn, is only ca. 5µm in diameter. The edge of the oral disc is lined with numerous setae, whilst the surface of the disc is covered with large numbers of small (<1µm in diameter) teeth-like structures, which presumably pierce through, and grip, the cuticle lining of the host's gill. Overall, these structures are thought to provide a 'vacuum seal' to assist in pumping of blood, via peristalsis, into the alimentary canal of the copepod host.