New tissue-dwelling species of Philometra Costa, 1845 and Philometroides Yamaguti, 1935 (Nematoda: Philometridae) from marine perciform fishes off the northern coast of Australia

Philometroides giginosantoroi n. sp. (Nematoda: Philometridae), a new muscle-infecting species in the Mediterranean moray (Muraena helena) revealed using integrative taxonomy

Philometroides Yamaguti, 1935 is a genus of dracunculoid nematodes of the family Philometridae Baylis & Daubney, 1926 comprising tissue-infecting species worldwide. In the present study, a new species of Philometroides is described from the Tyrrhenian Sea (central-western Mediterranean Sea) using integrative approaches such as light and scanning microscopy, histopathology and 18S rRNA sequencing. Philometroides giginosantoroi n. sp. found in the skeletal muscles of the Mediterranean moray Muraena helena can be distinguished from its congeners by a combination of morphological traits and in particular by having the oral aperture with 3 large sclerotized triangular oesophageal teeth. The molecular analyses and phylogenetic reconstructions support its status as a new taxon and placed it within a clade of tissue-infecting species, although also confirmed mismatches in the generic assignment of several species. Philometroides giginosantoroi n. sp. is the second species of the genus found in the Mediterranean Sea and in general in the European marine waters and the third species of the family known to infect the family Muraenidae.

Molecular phylogenetic relationship between Philometroides tahieli (Nematoda, Philometridae) and other philometrids from South America

In South America, the family Philometridae is represented by several genera and species. In particular, Philometra and Philometroides are the most speciose genera. In Argentina, only Philometroides tahieli has been reported so far. The main objective of this study was to analyze the phylogenetic relationship between Ps. tahieli and other South American philometrids using molecular data. The molecular analysis was performed using a female specimen of Ps. tahieli found on the opercular muscle of a juvenile Micropogonias furnieri from brackish waters in Argentina. Phylogenetic relationships were studied based on partial sequences of the 18S rDNA and 28S rDNA genes. In the 18S rDNA tree, Ps. tahieli was mainly grouped with other Philometroides from freshwater hosts from China, sharing the site of infection (head tissues or muscles). In the 28S rDNA tree, obtained with fewer sequences, Ps. tahieli is related species from subcutaneous tissues of head. This study contributes with information on philometrids and confirms the presence of different lineages among South American species, with Ps. tahieli representing a new one. Further studies on South American species using more molecular markers and new morphological characters will improve our knowledge of philometrid biodiversity and phylogeny.

Phylogenetic relationships of philometrid nematodes (Philometridae Baylis & Daubney, 1926) inferred from 18S rRNA, with molecular characterisation of recently described species

Nematodes of the family Philometridae Baylis & Daubney, 1926 (Dracunculoidea Stiles, 1907) are generally poorly known, and there are many taxonomic issues within the family. Philometrids are parasites of fish and are found in various locations throughout the host, including within the subcutaneous tissues and musculature, the abdominal cavity and gonads; vast sexual dimorphism often means the males are not collected, leading to many species being described solely on female characteristics. Although there have been a number of studies utilising molecular data, the vast majority of species are yet to be sequenced. This study undertook genetic sequencing of 15 recently described species of philometrids across 4 genera, many of which were from specimens collected from waters off Australia. All of the sequences obtained were closely related with representatives of the family Philometridae. Species were found to be distributed in the phylogenetic trees within 4 clades based on a combination of site of infection within the host and host habitat. Family of host and geographical location was not as important for position within the trees. Clade A contained philometrids collected from the abdominal cavities and head tissues of South American freshwater fish. Clade B contained philometrids primarily from the abdominal cavities of freshwater European cyprinids. Clade C contained philometrids primarily from the ovaries of marine fish. Clade D contained philometrids from the body tissues of marine and freshwater fish. The potential co-evolutionary patterns between philometrids and their fish hosts are highlighted as an area of future research. This research also highlighted the importance of correct identification of any sequenced specimen.

Morphological and genetic description of two new species of philometrid nematodes (Philometridae) parasitic in needlefishes (Belonidae) from estuaries of Florida, USA

Two new species of philometrid nematodes (Philometridae) from needlefishes (Belonidae) in Florida are described based on morphological and genetic characteristics: Philometra aequispiculata sp. n. (males and females) collected from the ovary of Strongylura marina (Walbaum) (type host) and Strongylura notata (Poey), and Philometra notatae sp. n. (females) from the swimbladder of S. notata. Both species are described and illustrated based on light and scanning electron microscopical examinations. Morphologically, P. aequispiculata sp. n. differs from all congeners mainly in the unique structure of the distal tip of the gubernaculum, whereas P. notatae sp. n. is mainly characterised by the presence of eight markedly large cephalic papillae of the outer circle in gravid and subgravid females, the body length of the gravid female (54 mm) and by the absence of caudal projections. Molecular characterisation of the new species was assessed from phylogenetic analysis of mitochondrial cytochrome c oxidase I (COI) and SSU rRNA small-subunit ribosomal RNA (SSU) sequences among closely related philometrids by way of Bayesian inference. Phylogenetic reconstructions based on COI and SSU sequences show each of the new species comprise discrete ancestor-descendent lineages.

Barracudia australiensis n. g., n. sp. (Nematoda: Philometridae) from the obtuse barracuda Sphyraena obtusata Cuvier (Perciformes: Sphyraenidae) off eastern Australia

Based on light and scanning electron microscopical studies, a new nematode parasite, Barracudia australiensis n. sp. (Philometridae), is described from the gall-bladder of the marine fish (obtuse barracuda) Sphyraena obtusata Cuvier (Sphyraenidae, Perciformes) from off the eastern Pacific coast of Australia, for which a new genus Barracudia n. g. is established. This new genus is mainly characterised by features found in the male: sickle-shaped, ventrally curved spicules, a gubernacum with a broad, dorsally bent distal portion and a markedly dorsoventrally elongated cloacal aperture. Based on these features, Barracudia spp. conspicuously differ from representatives of all other philometrid genera with known males. Philometra philippinensis Quiazon & Yoshinaga, 2013 is transferred to Barracudia as B. philippinensis (Quiazon & Yoshinaga, 2013) n. comb. Barracudia australiensis is the third nominal species of philometrids described from the Sphyraenidae and the 19th species of the Philometridae recorded from fishes in Australian waters.

The philometrid nematode Philometroides acreanensis n. sp. from the stomach wall of the catfish Pimelodus blochii in north-western Brazil

A new nematode species, Philometroides acreanensis n. sp. (Philometridae), is described from female specimens recovered from the stomach wall of the freshwater catfish Pimelodus blochii Valenciennes (Pimelodidae) collected in the Acre River (Amazon River basin), Acre State, Brazil. Based on examination by light and scanning electron microscopy, the new species differs from the two other South American congeneric species mainly in the body length of the gravid female (240-280 mm), the length of the oesophagus (1.25 mm in holotype) representing 0.5% of the entire body length, the range of cuticular embossment, as well as the location in the host (stomach), order of the fish host (Siluriformes) and the geographical distribution (Amazon River drainage system). This is the third known species of Philometroides Yamaguti, 1935 reported from South America. A key to species of Philometroides occurring in the fish of America is provided.