The egg shell of Huffmanela huffmani Moravec, 1987 forms three main layers: an outer vitelline layer, a middle chitinous layer, and an inner lipid layer. The vitelline layer, forming the superficial projections of the egg shell, comprises two parts: an outer electron-dense, and an inner electron-lucid part. The chitinous layer is differentiated into three parts: an outer homogenous electron-dense part, a lamellated part, and an inner electron-dense net-like part. The lipid layer comprises an outer net-like electron-lucid part, and an inner homogenous electron-lucid part. The polar plugs are formed by electron-lucid material with fine electron-dense fibrils.
The larval development of the nematode Contracaecum rudolphii (Rudolphi, 1819), a common parasite of the proventriculus of cormorants, was experimentally studied. Within the eggs cultivated in freshwater under laboratory temperatures of 20-22 °C, the developing larva undergoes two moults on days 4-5, attaining the third larval stage. Most of the ensheathed third-stage larvae, 291-457 µm long, hatch spontaneously from egg shells on days 5-6. Experiments have indicated that hatched ensheated third-stage larvae and those still inside egg capsules are already infective to copepods and fishes, which both can be considered paratenic (metaparatenic) hosts. Five copepod species, Acanthocyclops vernalis, Cyclops strenuus, Ectocyclops phaleratus, Eucyclops serrulatus and Megacyclops viridis, the isopod Asellus aquaticus and small carps Cyprinus carpio were infected by feeding them these larvae. In addition, 9 fish species, Alburnoides bipunctatus, Anguilla anguilla, Barbatula barbatula, Cyprinus carpio, Gobio gobio, Perca fluviatilis, Phoxinus phoxinus, Poecilia reticulata and Tinca tinca, were successfully infected by feeding them copepods previously infected with C. rudolphii third-stage larvae. In fishes, larvae from copepods penetrate through the intestinal wall to the body cavity, where, in a few weeks, they become encapsulated; the larvae substantially grow in fish, attaining the body length up to 4.87 mm. In carp fry, the nematode third-stage larvae survived for about 15 months (up to 18 months in fish infected directly, i.e., without copepods). One small cormorant (Phalacrocorax carbo sinensis) was successfully infected by feeding it with copepods harbouring C. rudolphii third-stage larvae.
Scanning electron microscopy examinations of trematode specimens belonging to Crepidostomum farionis (O.F. Müller, 1784) and C. metoecus Braun, 1900, collected from brown trout, Salmo trutta fario L., in the Czech Republic, made it possible to study their surface morphology including details not described previously. The tegument of both species bears numerous characteristic papillae around the oral sucker (in C. metoecus also around the ventral sucker) and the ventral and dorsal surfaces of the forebody, exhibiting a high degree of variability in numbers and arrangement, with tegumental bosses forming lateral fields on the forebody and minute sensory receptors with submerged cilia scattered on the surface of the dorsal part of the oral sucker. In addition to marked differences in the size, shape and position of the oral muscular lobes, both species distinctly differ in the number of genital pores: two separate pores in C. farionis and a single pore in C. metoecus.
The nematode Philometra rubra (Leidy, 1856) (Philometridae) is redescribed from subgravid females found in the abdominal cavity of the fish Morone saxatilis (Walbaum) from South Carolina, USA in November 2008. The species is characterized by the presence of 14 cephalic papillae arranged in two circles, a relatively long oesophagus with a distinct anterior inflation, and well-developed papilla-like caudal projections. Cephalic papillae of the external circle differ from those in other congeners in that the dorso-lateral and ventro-lateral papillae are large, dome-shaped, whereas the dorso-dorsal and ventro-ventral papillae are small.
The male of the gonad-infecting nematode Philometra filiformis (Stossich, 1896) (Philometridae) is for the first time described, based on specimens from the ovary of the marine fish Pagellus erythrinus (Linnaeus) from the Tyrrhenian Sea off Sicily, Italy. It is mainly characterized by the testis extending anteriorly nearly to the anterior end of body, the oesophagus without a usual anterior inflation, the absence of a dorsal barb or distinct transverse lamellae on the tip of the gubernaculum, the measurements of the spicules and the gubernaculum, and a fairly long body.
Two species of mayfly nymphs, Habroleptoides modesta (Hagen) and Habrophlebia lauta (Eaton) (Ephemeroptera: Leptophlebiidae), were found as suitable experimental intermediate hosts of the fish nematode Rhabdochona denudata (Dujardin, 1845) (Rhabdochonidae), an intestinal parasite of Palaearctic cyprinids. The parasite's eggs were obtained from nematode gravid females parasitizing the European chub, Leuciscus cephalus (L.), of the Rokytná River, Czech Republic. At the water temperature of 9°C, the eggs of R. denudata were ingested by the intermediate host and the hatched, toothed (with a minute cephalic boring tooth) first-stage larvae about 200 µm long penetrated into the body cavity of the mayfly. There the larvae grew and moulted twice (on 16-18 and 30-35 days p.i.) before attaining the third stage, which is already infective for the fish definitive host. Infective larvae of this stage were about 1.5 mm long and their morphology resembled that of adults except for the vestibule structure; they became encapsulated as in those of other congeneric species.
Based on light and scanning electron microscopical studies, the following five species of the Philometridae (Nematoda: Dracunculoidea) are described from female specimens collected from marine fishes off the southwestern coast of Java, Indonesia: Philometra lobotidis sp. n. from the abdominal cavity of the Atlantic tripletail Lobotes surinamensis (Bloch) (Lobotidae, Perciformes); Philometra javaensis sp. n. from the abdominal cavity of the immaculate puffer Arothron immaculatus (Bloch et Schneider) (Tetraodontidae, Tetraodontiformes); Philometra psettoditis sp. n. from the musculature of the Indian spiny turbot Psettodes erumei (Bloch et Schneider) (Psettodidae, Pleuronectiformes); Philometroides indonesiensis sp. n. from the musculature of the hound needlefish Tylosurus crocodilus crocodilus (Péron et Lesueur) (Belonidae, Beloniformes); and Philometroides trichiuri sp. n. from the dorsal fin of the largehead hairtail Trichiurus lepturus Linnaeus (type host) and the savalai hairtail Lepturacanthus savala (Cuvier) (both Trichiuridae, Perciformes). All these new species are distinguished from their congeners parasitizing marine fishes by morphological (mainly the shape and structure of the cephalic and caudal ends and of the oesophagus) and biometrical features. Besides previously known Philometra pellucida (Jägerskiöld, 1893) and Philometra ocularis Moravec, Ogawa, Suzuki, Miyazaki et Donai, 2002, they are the only nominal philometrid species recorded from Indonesian waters.
Recent examinations of some marine fishes from off the southern coast of Iraq revealed the presence of five species of Philometra Costa, 1845 (Nematoda: Philometridae): Philometra arabiensis sp. n. (males and females) from the ovary of the shrimp scad Alepes djedaba (Forsskål) (Carangidae, Carangiformes), Philometra psettoditis Moravec, Walter et Yuniar, 2012 (females) from the body cavity of the Indian halibut Psettodes erumei (Bloch et Schneider) (Psettodidae, Pleuronectiformes), Philometra terapontis Moravec, Gopalakrishnan, Rajkumar, Saravanakumar et Kaliyamoorthy, 2011 (female) from the ovary of the jarbua terapon Terapon jarbua (Forsskål) (Terapontidae, Centrarchiformes), Philometra sp. (females) from the ovary of the Arabian blackspot threadfin Polydactylus mullani (Hora) (Polynemidae, Carangariformes) and Philometra sp. 2 of Moravec et al. (2016a) (females) from the ovary and body cavity of the bartail flathead Platycephalus indicus (Linnaeus) (Platycephalidae, Perciformes). Philometra arabiensis sp. n. is mainly characterised by the length of spicules (198-243 µm) and gubernaculum (75-99 µm), the gubernaculum/spicule length ratio (1 : 2.33-2.79), the structure of the gubernaculum distal portion and the male caudal end, and the body length of males (1.86-2.73 mm). The present findings of P. psettoditis and P. terapontis in fishes of the Arabian Gulf represent new geographical records for these parasites.
The nematode Goezia spinulosa (Diesing, 1839) (Raphidascarididae) is redescribed based on specimens found in the stomach and intestine of the naturally infected arapaima Arapaima gigas (Schinz) from the Mexiana Island, Amazon River Delta, Brazil. Light and electron microscopy examinations revealed some previously unreported or inaccurately described morphological features in the species, such as the position of the excretory pore, phasmids in the male or the number (4) of postanal papillae. The morphology of G. spinulosa is compared with that of other four congeneric species parasitizing freshwater fishes in South America. This nematode seems to be one of the most pathogenic parasites of A. gigas in the Mexiana Island, which are responsible for a high mortality of cultured arapaima fingerlings. Apparently, the source of G. spinulosa infection for arapaima fingerlings cultured in tanks was the infected plankton collected in the localities inhabited by wild arapaimas. Therefore, control measures should include the sterilisation of the plankton before its use as food for fish. A rare infection of Eustrongylides sp. larvae (Dioctophymatidae) in arapaima fingerlings was also found (new host record); the larvae were inside swellings on the body surface.