Adult specimens of five little-known species of spiruridan nematodes (Spirurida) were collected during occasional examinations of some fishes from the Poonch River in Jammu and Kashmir, India: Procamallanus (Spirocamallanus) bilaspurensis Gupta et Duggal, 1973 in Mastacembelus armatus (Lacépède) (Mastacembelidae, Synbranchiformes), Rhabdochona (Rhabdochona) indica Moravec, Scholz, Ash et Kar, 2010 in Crossocheilus latius (Hamilton) (Cyprinidae, Cypriniformes), Rhabdochona (Rhabdochona) turkestanica (Skryabin, 1917) in Schizothorax richardsonii (Gray) (Cyprinidae, Cypriniformes) and both Rhabdochona (Rhabdochona) hospeti Thapar, 1950 and Rhabdochona (Globochona) cf. chodukini Osmanov, 1957 in Tor putitora (Hamilton) (Cyprinidae, Cypriniformes); besides these, unidentifiable physalopterid larvae were recorded from M. armatus and T. putitora. Their detailed light and electron microscopical studies revealed some taxonomically important, previously not observed features and made possible their redescription. Fourth-stage larvae of P. (S.) bilaspurensis and R. (R.) turkestanica are described for the first time. The latter is resurrected as an independent species. The following are considered to be species inquirendae: a total of nine poorly described species of Rhabdochona Railliet, 1916 from T. putitora in Balochistan, Pakistan, all listed in the monograph of Kakar et al. (2011), plus an additional 15 species of the genus reported from cyprinids and a catfish in the same region (Balochistan) by the same authors. Also three congeneric species from India (R. nemacheili Rautela et Malhotra, 1982, R. putitora Kaur et Khera, 1991 and R. tori Gupta et Srivastava, 1982) and one from Pakistan (R. charsaddiensis Siddiqi et Khattak, 1984) should be considered as species inquirendae due to their poor descriptions. The names of Rhabdochona putitori Anjum, 2013, R. indusi Soofi, Birmani et Dharejo, 2017 and R. sindhicus Soofi, Birmani, Dharejo, Abbasi et Ghachal, 2020 are invalid according to the International Code of Zoological Nomenclature.
About 300 species belonging to four superfamilies (Gnathostomatoidea, Habronematoidea, Physalopteroidea and Thelazioidea) of the nematode suborder Spirurina are known as the adult parasites of freshwater, brackish-water and marine fishes. They are placed in four families, of which the Gnathostomatidae, including Echinocephalus with a few species and the monotypic Metaleptus, are parasites of elasmobranchs, whereas Ancyracanthus contains one species in teleosts; the Physalopteridae is represented in fish by four genera, Bulbocephalus, Heliconema, Paraleptus and Proleptus, each with several species in both elasmobranchs and teleosts. The majority of fish spirurines belongs to the Rhabdochonidae, which includes 10 genera (Beaninema, Fellicola, Hepatinema, Heptochona, Johnstonmawsonia, Megachona, Pancreatonema, Prosungulonema, Rhabdochona and Vasorhabdochona) of species parasitizing mainly teleosts, rarely elasmobranchs, and the Cystidicolidae with about 23 genera (Ascarophis, Caballeronema, Capillospirura, Comephoronema, Crenatobronema, Cristitectus, Ctenascarophis, Cyclozone, Cystidicola, Cystidicoloides, Johnstonmawsonoides, Metabronema, Moravecnema, Neoascarophis, Parascarophis, Prospinitectus, Pseudascarophis, Pseudoproleptus, Salvelinema, Similascarophis, Spinitectoides, Spinitectus, Sterliadochona), with many species parasitic in teleosts only. Because of difficulties in studying fish spirurines, associated with their morphological and biological peculiarities, most species of these parasites are poorly known. It is apparent that their present classification system does not reflect phylogenetic relationships and a taxonomic revision of this nematode group, based on detailed morphological (including SEM and TEM), life history and molecular studies of individual species, is quite necessary. In Cystidicolidae, several genera have been based on details in the cephalic structures visible only with the aid of SEM, but it will be evident whether or not these tiny features are of generic importance only when more cystidicolids are described using SEM and comparative molecular data become available. Data on the biology of fish spirurines are scarce. In known cases, their life cycles involve aquatic arthropods (crustaceans or insects) as intermediate hosts, in which, sometimes, the larvae undergo a precocious development and may even attain adulthood and become gravid in these invertebrates; sometimes, fish paratenic hosts are known to occur in cystidicolids parasitizing as adults piscivorous definitive hosts. Some spirurine species are pathogenic and are known as causative agents of serious fish diseases. and Consequently, further detailed studies on fish spirurines are significant not only from the theoretical viewpoint, but they may also have practical implications.
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.