A review of the currently recognised opecoelid cercariae, including the identification and emergence ecology of Cercaria capricornia XII (Digenea: Opecoelidae) from Nassarius olivaceus (Gastropoda: Nassariidae) in Central Queensland, Australia

Molecular characterisation of three species of Coitocaecum (Digenea: Opecoelidae) infecting Clinus superciliosus (Clinidae) in South Africa, with description of Coitocaecum brayi sp. n

The genus Coitocaecum Nicoll, 1915 is part of the most speciose digenean family, the Opecoelidae Ozaki, 1925, which is found globally in both freshwater and marine fishes. Fifteen opecoelid species have been reported from marine fishes in South Africa, yet only one species of Coitocaecum has been described from this region: Coitocaecum capense Bray, 1987. During an explorative study of the digeneans of the endemic, intertidal fish Clinus superciliosus (Linnaeus) from the Saldanha Bay area, Cape Town harbour, Hermanus, the Tsitsikamma section of the Garden Route National Park and Chintsa East in South Africa, a total of three distinct species of Coitocaecum were identified based on morphological and molecular (28S rDNA, ITS1-5.8S-ITS2 rDNA and COI mtDNA) data: the previously mentioned C. capense, Coitocaecum brayi sp. n. and a third, unnamed species. We provide the first molecular characterisation of species of Coitocaecum from South Africa, accompanied by detailed morphological descriptions. This study illustrates the importance of an integrated taxonomic approach, especially when studying species with similar morphology. These findings further emphasise the lack of information on the true diversity and molecular data for trematodes of marine fishes in South Africa, creating a great capacity for future explorative taxonomic studies and highlighting the use of intertidal areas for conducting such research.

New insights on the role of the holoplanktonic mollusk Firoloida desmarestia (Gastropoda: Pterotracheidae) as host for digenetic trematodes

Interactions of holoplanktonic mollusks with symbionts and parasites are poorly known. We investigated the ecology of infection (prevalence, intensity, and abundance) in Firoloida desmarestia, caught during two sampling campaign sessions in 2012, off the Baja California Peninsula, Mexico (IMECOCAL, 83 stations) and a coastal research center near La Sorpresa Beach, Baja California Sur, in the Gulf of California (14 stations). Only females of F. desmarestia were parasitized. Hemiuroidea parthenita rediae infected 1% of F. desmarestia population at IMECOCAL, whereas young unencysted metacercariae stages of Opechona pyriformis (Lepocreadiidae) parasitized 6.6% of the same host species at La Sorpresa. Overall, finding of rediae and metacercariae represent new geographical and host records and shows that F. desmarestia has a dual host function in the life cycle of trematodes. As first intermediate host, F. desmarestia harbors hemiuroid rediae, functioning as the source of infection to other zooplanktonic groups by dispersing successive cercariae. As second intermediate hosts, it harbors infective unencysted metacercariae stages of O. pyriformis, which parasitize nektonic predators (fish), most likely through trophic interaction. Our results suggest that some trematodes are able to spend their entire life cycle infecting only pelagic hosts. Parasite-F. desmarestia interaction is shown in a conceptual model, where we propose that transmission of trematodes may occur between individuals of F. desmarestia within the same swarm. Relevance of F. desmarestia as a potential host in which life cycle abbreviation of trematodes may take place is discussed. This is the first quantitative study of helminth interaction on F. desmarestia in the Eastern Pacific.

The phylogenetic position of Choerodonicola Cribb, 2005 (Digenea: Opecoelidae) with a partial life-cycle for a new species from the blue-barred parrotfish Scarus ghobban Forsskål (Scaridae) in Moreton Bay, Australia

Choerodonicola Cribb, 2005 is a minor genus of opecoelid trematodes defined for species with exceptionally small eggs but otherwise generalised morphology. Four species are currently recognised, all from fishes collected in Japanese waters but each from different perciform families: a labrid, a scarid, a sparid and pinguipeds. We report on a new species, Choerodonicola arothokoros n. sp., from the blue-barred parrotfish Scarus ghobban Forsskål (Scaridae) collected in subtropical waters of Moreton Bay, south-east Queensland, Australia. Using genetic sequence data for the ITS2 rDNA marker, we matched adult C. arothokoros to intramollsucan stages discovered in an intertidal gastropod Herpetopoma atratum (Gmelin) (Vetigastropoda: Chilodontidae) collected in close proximity to the fish hosts. Notably, the cercariae lack a penetration stylet and are among the smallest known in the Opecoelidae. We provide the first assessment of the phylogenetic position of Choerodonicola based on sequence data generated for the phylogenetically informative 18S and 28S rRNA coding regions, for C. arothokoros and also C. renko Machida, 2014, which we recollected from the yellowback seabream Dentex hypselosomus Bleeker from the fish market in Minabe, Wakayama Prefecture, Japan. In our analyses, species of Choerodonicola resolved to neither of the major marine Plagioporinae (sensu lato) clades, clustering instead with Trilobovarium parvvatis Martin, Cutmore & Cribb, 2017, Podocotyloides parupenei (Manter, 1963) Pritchard, 1966 and Macvicaria magellanica Laskowski, Jeżewski & Zdzitowiecki, 2013. This clade is phylogenetically distinctive such that it has the potential to be recognised as a new opecoelid subfamily, but further investigation is required to establish the bounds for such a grouping and to determine the morphological and/or life-history patterns reflected by the phylogeny. Finally, we propose C. interruptus (Manter 1954) n. comb. for a species previously recognised in Plagioporus Stafford, 1904 and known only from Pseudolabrus miles (Schneider & Forster), a labrid endemic to New Zealand.

The molecular phylogeny of the digenean family Opecoelidae Ozaki, 1925 and the value of morphological characters, with the erection of a new subfamily

Large and small rDNA sequences of 41 species of the family Opecoelidae are utilised to produce phylogenetic inference trees, using brachycladioids and lepocreadioids as outgroups. Sequences were newly generated for 13 species. The resulting Bayesian trees show a monophyletic Opecoelidae. The earliest divergent group is the Stenakrinae, based on two species which are not of the type-genus. The next well-supported clade to diverge is constituted of three species of Helicometra Odhner, 1902. Based on this tree and the characters of the egg and uterus, a new subfamily, the Helicometrinae, is erected and defined to include the genera Helicometra, Helicometrina Linton, 1910 and Neohelicometra Siddiqi et Cable, 1960. The subfamily Opecoelinae is found to be monophyletic, but the Plagioporinae is paraphyletic. The single representative of the Opecoelininae (not of the type genus) is nested within a group of deep-sea 'plagioporines'. The two representatives of the Opistholebetidae are embedded within a group of shallow-water 'plagioporine' species. The Opistholebetidae is reduced to subfamily status pro tem as its morphological and biological characteristics are distinctive. This implies that as opecoelid systematics develops with more molecular evidence, several further subfamilies will be recognised. Many of the morphological characters were found to be homoplasious, but the characters defining the Helicometrinae and Opecoelinae, such as filamented eggs, reduced cirrus-sac and uterine seminal receptacle, are closely correlated with the inferred phylogeny.