Members of the Philometridae represent the most important group of dracunculoid nematodes parasitizing fishes. In his monograph treating the Dracunculoidea, Moravec (2006) reported a total of 11 genera and 105 species of philometrids parasitizing freshwater, brackish-water and marine fishes. However, during the last six years (2007-2012), an additional 42 new species of Philometridae have been described, representing a 40% increase of the number of nominal species. Most of these species (30) belong to Philometra Costa, 1845, mainly represented by parasites of marine fishes, a few others (8) to Philometroides Yamaguti, 1935, and a single one to each of the following genera: Caranginema Moravec, Montoya-Mendoza et Salgado-Maldonado, 2008, Dentiphilometra Moravec et Wang, 2002, Dentirumai Quiazon et Moravec, 2013* and Spirophilometra Parukhin, 1971. Moreover, three new genera, Afrophilometra Moravec, Charo-Karisa et Jirků, 2009, Caranginema and Dentirumai, were erected. Representatives of seven genera, Afrophilometra, Buckleyella Rasheed, 1963, Caranginema, Dentiphilometra, Dentirumai, Paraphilometroides Moravec et Shaharom-Harrison, 1989 and Rumai Travassos, 1960, were studied using scanning electron microscopy (SEM) for the first time. Thirteen known but poorly described philometrid species were redescribed and, in some species of Caranginema and Philometra, previously unknown conspecific males were discovered and described. The male surface ultrastructure studied by SEM provided new taxonomically important features for species distinction. Gene sequencing was used in several recent studies and advanced our understanding of phylogenetic interrelationships among representatives of seven genera (Afrophilometra, Alinema Rasheed, 1963, Caranginema, Nilonema Khalil, 1960, Philometra, Philometroides and Rumai) and of the extent of the biodiversity of philometrids. New data were obtained on the biology and pathogenicity of several species of Nilonema, Philometra, Philometroides and Rumai. The need to carry out surveys in order to find males and to use SEM and gene sequencing to identify philometrids is emphasized. Appropriate quantitative methods to determine the impact of philometrids in ovarian tissue on host fecundity are recommended. Further detailed studies on philometrids would be significant not only from the theoretical viewpoint, but also because of their practical implications. A list of philometrid nematode species by continents is provided.
Morphological data and molecular analyses are used to describe the taxonomy of philometrid nematodes of the genus Philometra Costa, 1845, found in the gonads of marine fishes in Japan. A new Philometra species, P. sawara sp. n., is described based on male and female specimens collected from the gonads of Scomberomorus niphonius (Cuvier) (Japanese Spanish mackerel). Two additional species, Philometra nemipteri Luo, 2001 and Philometra sciaenae Yamaguti, 1941, are confirmed as valid species and are redescribed based on specimens collected from the gonads of Nemipterus virgatus (Houttuyn) (golden threadfin bream) and Pennahia argentata (Houttuyn) (silver croaker), respectively. Male P. nemipteri are first reported and described in this study. Redescriptions of female P. nemipteri and male and female P. sciaenae were also necessary based on our morphological observations. A molecular comparison of the internal transcribed spacer 2 (ITS2) region of the ribosomal DNA between P. sawara, P. nemipteri, P. sciaenae, and previously reported philometrid nematodes from the genus Philometra and Philometroides Yamaguti, 1935 supports the conclusion that the three Philometra species in the current study are independent. An ITS2-derived neighbour-joining tree, consisting of both the current specimens and previously described Philometra and Philometroides species, is also presented.
Ichthyofilaria argentinensis Incorvaia, 1999 (Nematoda: Philometridae) is redescribed from type specimens and from parasites collected from the swim bladder of Argentine hakes Merluccius hubbsi Marini, 1933 caught at the Gulf of San Jorge (46°30'S, 66°30'W), Argentine Sea, in July, 1998. Sixteen out of 80 hakes (20%) were found to be parasitised by gravid females of this philometrid. After revision of both these nematodes and type material, the following differences from the original description of the species were observed: (a) cuticle with fine transverse striations, instead of smooth cuticle; (b) presence of cephalic papillae and a pair of amphids; (c) absence of swellings in the oesophagus; (d) oesophageal gland appendix very large and lobulate rather than small and vermiform, and (d) presence of vulva and vagina. The morphological features given in the redescription allow the confirmation of the identity of I. argentinensis as a valid species and to distinguish it from other members of the genus.
Based on the original description, the nematode genus Piscinema Gambhir et Ng, 2014 and its type species, P. barakensis [sic] Gambhir et Ng, 2014 (probably a misidentified physalopterid larvae), are removed from the Philometridae, where they were allocated; they are considered a genus inquirendum and incertae sedis and a species inquirenda, respectively. The poorly described nematode Rhabdochona carpiae Nimbalkar, Deolalikar et Kamtikar, 2013 (Rhabdochonidae) appears largely fabricated and is regarded a species dubia.