Rodney A. Bray

Species of Hexangium (Microscaphidiidae) were collected from 12 species of rabbitfishes (Siganidae) from multiple Indo-West Pacific locations: three on the Great Barrier Reef in Queensland, two in south-east Queensland, Ningaloo Reef in Western Australia, New Caledonia and Japan; no specimens were found from Palau or French Polynesia. Parallel molecular ( cox 1 mtDNA, ITS2 and 28S rDNA) and morphological analyses, together with consideration of host and geographical distribution, lead us to recognise six species. Specimens from Siganus fuscescens (Houttuyn) from Japan are identified as the type species, H. sigani Goto & Ozaki, 1929, which was originally described from S. fuscescens from off Japan. Hexangium affinum Tubangui & Masiluñgan, 1944, originally described from Siganus javus (Linnaeus) from the Philippines but previously considered a synonym of H. sigani , is reinstated, and H. secundum Annereaux, 1947 is considered its junior synonym. Four new species are described: H. urabeae n. sp., H. kuramochii n. sp., H. robustum n. sp. and H. reimeri n. sp. Based on morphology alone, individual specimens of several combinations of these species are difficult to distinguish. Although none of the combinations of species are entirely mutually cryptic, we consider taxonomy of this genus to be dependent on molecular analysis; morphological distinction of species requires substantial numbers of well-preserved specimens. Most species of Siganus examined harbour two or three species of Hexangium ; sometimes one species is dominant, but in several two species were both common. All six Hexangium species recognised here have been found in multiple locations; four species were found at each of two Great Barrier Reef sites.

We report trematodes conforming to the generic concept of Parachrisomon Madhavi, 2008, infecting multiple species of goatfishes (Mullidae) from Moreton Bay (south-eastern Queensland) and off Lizard Island (northern Great Barrier Reef) on the eastern coast of Australia, and from Ningaloo Reef on the western coast. Initial morphological analyses suggested the possible presence of multiple species; however, no morphological distinctions proved consistent. Molecular analyses demonstrate a distinction between western and eastern Australian samples, especially in mt cox 1 sequence data, but the differences are interpreted as intraspecific geographical variation. Specimens from all localities share a bipartite terminal organ with an irregularly shaped and lobed anterior part; the other eight species of Parachrisomon are reported with unspecialised, bipartite terminal organs. We recognise the specimens as representing a new species, Parachrisomon debonoae n. sp., that exhibits significant intraspecific morphological variation, especially in body size, pharynx size, and shape and size of the ovary and testis. Additionally, we report novel molecular data for Parachrisomon delicatus (Manter & Pritchard, 1961) Madhavi, 2008.

The description and delineation of trematode species is a major ongoing task. Across the field there has been, and currently still is, great variation in the standard of this work and in the sophistication of the proposal of taxonomic hypotheses. Although most species are relatively unambiguously distinct from their congeners, many are either morphologically very similar, including the major and rapidly growing component of cryptic species, or are highly variable morphologically despite little to no molecular variation for standard DNA markers. Here we review challenges in species delineation in the context provided to us by the historical literature, and the use of morphological, geographical, host, and molecular data. We observe that there are potential challenges associated with all these information sources. As a result, we encourage careful proposal of taxonomic hypotheses with consideration for underlying species concepts and frank acknowledgement of weaknesses or conflict in the data. It seems clear that there is no single source of data that provides a wholly reliable answer to our taxonomic challenges but that nuanced consideration of information from multiple sources (the ‘integrated approach’) provides the best possibility of developing hypotheses that will stand the test of time.

The techniques employed to collect and store trematodes vary between research groups, and although these differences are sometimes necessitated by distinctions in the hosts examined, they are more commonly an artefact of instruction. As a general rule, we tend to follow what we were taught rather than explore new techniques. A major reason for this is that there are few technique papers in the published literature. Inspired by a collaborative workshop at the Trematodes 2024 symposium, we outline our techniques and processes for collecting adult trematodes from fishes and discuss the improvements we have made over 40 years of dissections of 20,000+ individual marine fishes. We present these techniques for two reasons: first, to encourage unified methods across the globe, with an aim to produce optimally comparable specimens across temporal periods, across geographic localities, and between research groups; and second, as a resource for inexperienced researchers. We stress the importance of understanding differences in host biology and the expected trematode fauna, which ultimately enables organised and productive dissections. We outline our dissection method for each key organ separately, discuss handling, fixation, and storage methods to generate the most uniform and comparable samples, and explore ethical considerations, issues of accurate host identification, and the importance and potential of clear record keeping.

With a long coastline stretching from tropical to subtropical climate zones, and an immense exclusive economic zone with over 4000 islands, the Vietnamese marine waters support a rich and biodiverse parasite fauna. Although the first parasitological record was in 1898, systematic studies of the parasite fauna have increased during the last 50 years. This comprehensive review covers the current state of knowledge of marine fish parasites in Vietnam and lists 498 species found in 225 fish species, and their geographical distribution. In addition, 251 marine parasite species have newly been added to the already known fauna of 247 species since 2006 (more than two-fold increase). The most speciose group was the Digenea, which accounted for 43% of the total parasite species biodiversity, followed by Monogenea (23.5%), Crustacea (11.6%), Nematoda, and Acanthocephala (8.0% each). The shallow and muddy Gulf of Tonkin showed a rich parasite fauna, accounting for 66.3% of the whole marine parasite fauna of Vietnam, with Digenea accounting for 51% of the regional total parasite richness, followed by Monogenea (27%), Acanthocephala (8.8%), and Nematoda (5.8%). Only a few species belonged to Hirudinea, Myxozoa, and Cestoda, suggesting that these taxa may be understudied. Despite significant progress in studies of marine fish parasites in Vietnam since 2006, only about 12% and 13% of the total fish species have been examined for parasites in the whole country and the Gulf of Tonkin, respectively.

A new species of lepocreadiid, Opechonoides opisthoporusn. sp., is described infecting 12 pomacentrid fish species from the Great Barrier Reef, Australia, with Abudefduf whitleyi Allen & Robertson as the type-host. This taxon differs from the only other known member of the genus, Opechonoides gure Yamaguti, 1940, in the sucker width ratio, cirrus-sac length, position of the testes, position of the pore of Laurer’s canal, and relative post-testicular distance. The new species exhibits stenoxenic host-specificity, infecting pomacentrids from seven genera: Abudefduf Forsskål, Amphiprion Bloch & Schneider, Neoglyphidodon Allen, Neopomacentrus Allen, Plectroglyphidodon Fowler & Ball, Pomacentrus Lacépède and Stegastes Jenyns. Phylogenetic analyses of 28S rDNA sequence data demonstrate that O. opisthoporusn. sp. forms a strongly supported clade with Prodistomum orientale (Layman, 1930) Bray & Gibson, 1990. The life cycle of this new species is partly elucidated on the basis of ITS2 rDNA sequence data; intermediate hosts are shown to be three species of Ctenophora. New host records and molecular data are reported for Lepocreadium oyabitcha Machida, 1984 and Lepotrema amblyglyphidodonis Bray, Cutmore & Cribb, 2018, and new molecular data are provided for Lepotrema acanthochromidis Bray, Cutmore & Cribb, 2018 and Lepotrema adlardi (Bray, Cribb & Barker, 1993) Bray & Cribb, 1996. Novel cox1 mtDNA sequence data showed intraspecific geographical structuring between Heron Island and Lizard Island for L. acanthochromidis but not for L. adlardi or O. opisthoporusn. sp.

The taxonomy of species of Bivesicula Yamaguti, 1934 is analysed for samples from holocentrid, muraenid and serranid fishes from Japan, Ningaloo Reef (Western Australia), the Great Barrier Reef (Queensland), New Caledonia and French Polynesia. Analysis of three genetic markers (cox1 mtDNA, ITS2 and 28S rDNA) identifies three strongly supported clades of species and suggests that Bivesicula as presently recognized is not monophyletic. On the basis of combined morphological, molecular and biological data, 10 species are distinguished of which five are proposed as new. Bivesicula Clade 1 comprises seven species of which three are effectively morphologically cryptic relative to each other; all seven infect serranids and four also infect holocentrids. Bivesicula Clade 2 comprises three species of which two are effectively morphologically cryptic relative to each other; all three infect serranids and one also infects a muraenid. Bivesicula Clade 3 comprises two known species from apogonids and a pomacentrid, and forms a clade with species of Paucivitellosus Coil, Reid & Kuntz, 1965 to the exclusion of other Bivesicula species. Taxonomy in this genus is made challenging by the combination of low resolving power of ribosomal markers, the existence of regional cox1 mtDNA populations, exceptional and unpredictable host-specificity and geographical distribution, and significant host-induced morphological variation.