Opegaster Ozaki, 1928 is one of the most species-rich genera of the trematode family Opecoelidae, commonly found in marine teleost fishes. This study describes a new species of Opegaster of the intertidal fish species Labrisomus xanti Gill (Labrisomidae) (type host) and Tomicodon zebra (Jordan et Gilbert) (Gobiesocidae) from the coast of Oaxaca, Mexican Pacific. Opegaster mezcal sp. n. is characterised by the absence of papillae on the ventral sucker and the size and shape of the testes. Sequences of the D1-D3 domains from large subunit from nuclear DNA (28S) were generated for the new species and for another opecoelid species, Opecoelus adsphaericus Manter et Van Cleave, 1951. The new sequences of Opegaster mezcal sp. n. formed a clade, which is sister to O. adsphaericus. However, the phylogenetic relationships among genera of Opecoelinae remain unresolved because few species have been analysed; the addition of further taxa is necessary to better understand the evolution of the subfamily.

• Keywords
• Digenea, Mexico, Oaxaca, Plagiorchiida, marine fish, taxonomy,
• MeSH
• DNA, Helminth genetics   MeSH
• Phylogeny MeSH
• Trematode Infections * veterinary   parasitology   epidemiology   MeSH
• Fish Diseases * parasitology   epidemiology   MeSH
• Perciformes * parasitology   MeSH
• RNA, Ribosomal, 28S genetics   MeSH
• Trematoda * classification   genetics   anatomy & histology   isolation & purification   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Geographicals
• Mexico epidemiology   MeSH
• Pacific Ocean MeSH
• Names of Substances
• DNA, Helminth MeSH
• RNA, Ribosomal, 28S MeSH

Molecular and morphological data were gathered for specimens of species of Macvicaria Gibson & Bray, 1982 and Pseudopycnadena Saad-Fares & Maillard, 1986 (Digenea: Opecoelidae) collected from two sparid fishes, Diplodus vulgaris (Geoffroy Saint-Hilaire) and Sparus aurata L., off the Algerian coast of the Western Mediterranean. Phylogenetic analyses based on ITS1-5.8S-ITS2 and partial 28S rDNA sequences provided evidence for the distinct species status of eight Mediterranean species of Macvicaria. Novel molecular data are provided for four species, M. gibsoni n. sp. and M. crassigula (Linton, 1910) (sensu stricto) based on specimens from D. vulgaris, and M. mormyri (Stossich, 1885) and M. maamouriae Antar, Georgieva, Gargouri & Kostadinova, 2015 based on specimens from S. aurata; descriptions of the molecular voucher material of the former three species are provided. Two species were delineated within the "crassigula" species complex of Macvicaria, M. gibsoni n. sp. and M. crassigula (s. str.), the distinctive differentiating features being the distribution of the dorsal vitelline fields in the forebody, confluent in M. gibsoni n. sp. and non-confluent in M. crassigula (s. str.), and the molecular data for both markers. Sequences associated with morphological description are also provided for the type-species of Pseudopycnadena, P. fischthali Saad-Fares & Maillard, 1986, based on material from D. vulgaris.

• MeSH
• Species Specificity MeSH
• Phylogeny * MeSH
• DNA, Ribosomal Spacer genetics   MeSH
• Perciformes parasitology   MeSH
• DNA, Ribosomal genetics   MeSH
• RNA, Ribosomal, 28S genetics   MeSH
• Trematoda anatomy & histology   classification   genetics   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA, Ribosomal Spacer MeSH
• DNA, Ribosomal MeSH
• RNA, Ribosomal, 28S MeSH

A new species of microphallid, Longiductotrema tethepae n. sp., is reported from a muraenid eel Gymnothorax pseudothyrsoideus (Bleeker) on the northern Great Barrier Reef. The new species is described based on adults from Gy. pseudothyrsoideus and metacercariae from a grapsid crab, Grapsus albolineatus Latreille in Milbert, collected from off Lizard Island, Queensland, Australia. The new species is assigned to Longiductotrema Deblock & Heard, 1969 based on morphological characters (presence of a cirrus-sac; a long metraterm, intensively ensheathed by gland-cells; an entirely postcaecal uterus; vitellarium composed of two lateral clusters each of about ten follicles, situated in the testicular and post-testicular areas). Longiductotrema tethepae n. sp. is the third species assigned to the genus, differing from its congeners in having a distinctly larger body dimensions, a smaller pharynx in relation to oral sucker, the anterior limits of the vitelline fields at the level of the testes (vs at the level of the ovary) and in its parasitism of a muraenid fish (vs birds). Additionally, the new species differs from L. floridense Deblock & Heard, 1969 in having a shorter metraterm and from L. scandolensis Deblock & Bartoli, 1988 in having a less elongate forebody in relation to body length, shorter caeca and prepharynx, and slightly larger eggs. Phylogenetic analyses, based on partial 28S rRNA gene sequences, showed that the present species is sister to all other microphallids for which sequence data are available. This is the fourth report of a microphallid from a marine eel, the first from the Muraenidae Rafinesque and the first from a marine fish in the Indo-west Pacific. A summary of all species of the Microphallidae parasitising fish is provided.

• MeSH
• Eels parasitology   MeSH
• Species Specificity MeSH
• Phylogeny * MeSH
• RNA, Ribosomal, 28S genetics   MeSH
• Trematoda anatomy & histology   classification   genetics   MeSH
• Animals MeSH
• Check Tag
• Male MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Geographicals
• Australia MeSH
• Names of Substances
• RNA, Ribosomal, 28S MeSH