A comparative morphological study of specimens of Ligophorus spp. from Mugil cephalus in western Mediterranean and the Black Sea localities has been carried out, indicating the presence of 2 distinct forms, i.e., Ligophorus chabaudi and Ligophorus cephali n. sp. A detailed description of the latter and an up-to-date redescription of L. chabaudi are provided. The existence of these 2 morphological species was additionally supported by principal component analysis based on 19 metric characters of 87 specimens arranged in samples defined by parasite species and geographical locality. The analysis indicated consistent differences between species but not between localities; this pattern was well supported by jackknife procedures. Linear discriminant analyses showed that the main metric differences between the 2 species were attributable to the lengths of the dorsal and ventral bars and to the uncinulus length; use of the first 2 variables was enough to allocate all specimens studied to either form. The erection of L. cephali n. sp. raises the number of sympatric Mediterranean species of Ligophorus on M. cephalus to 3. The known geographical ranges of these species are compared.

Four gobiid species, Babka gymnotrachelus, Neogobius melanostomus, Neogobius fluviatilis, and Proterorhinus semilunaris, were parasitologically studied in different localities of the Dnieper and Vistula river basins. The highest number of parasitic species was found in N. fluviatilis (35 taxa). The parasite fauna of N. melanostomus, B. gymnotrachelus, and P. semilunaris consists of 23, 22, and 15 taxa, respectively. The species accumulation curves show stable accumulation of parasite species by all four fish hosts along the studied part of the corridor, from the Dnieper Estuary to the Vistula River delta. The plot reveals also that the studied gobies lose the parasites common in the host native range and accept new parasites from the colonized area. In the case of N. melanostomus, it complies with the enemy release hypothesis, as the parasite load was low in the invaded area if compared to the native range. The three other alien gobies are vector for Gyrodactylus proterorhini in the Baltic basin. Moreover, populations of this alien monogenean tend to be more abundant in their new range in comparison with the Black Sea basin. In general, the number of parasite species in the colonized area was of the same rank as in the native one for N. fluviatilis, and even higher for B. gymnotrachelus. This results from accumulating new parasite species along the gobiid invasion route. In particular, the N. fluviatilis, B. gymnotrachelus, and P. semilunaris lost some of their native parasites and gained the local ones after entering the post-dam part of the Vistula River; it can be interpreted as a partial escape from parasites.

Comparative morphology and multivariate morphometric analysis of monogeneans collected on flathead mullets Mugil cephalus from 2 Russian localities of the Japan Sea revealed the presence of 3 new species of Ligophorus, namely, L. domnichi n. sp., L. pacificus n. sp., and L. cheleus n. sp., which are described herein. So far, only 1 species of dactylogyrid monogenean identified as Ligophorus chabaudi was known on flathead mullets in this sea, but after comparison with the present material, we propose that this form actually represents L. domnichi n. sp. Results support previous zoogeographical evidence, suggesting that flathead mullets from different seas harbor different species complexes of Ligophorus. One interesting finding is that the 3 new species have a U-shaped ovary, whereas ovate ovaries have been reported in previous descriptions of species of the genus, e.g., L. vanbenedenii, L. parvicirrus, L. imitans, and L. chongmingensis. The U-shaped ovary was revealed only when the worms were observed in lateral view. The additional examination of L. vanbenedenii, L. parvicirrus, L. imitans, and L. pilengas specimens from our collections also revealed a U-shaped ovary in these forms as well. Further studies should establish whether or not this character is shared by all members of the genus.

We recognize four species in the Neoechinorhynchus agilis complex. We studied specimens of Neoechinorhynchus (Hebesoma) personatus Tkach, Sarabeev & Shvetsova, 2014 from Mugil cephalus in the Mediterranean Sea off Tunisia and in the Black Sea, and also specimens of Neoechinorhynchus ponticus n. sp. from Chelon auratus Risso in the Black Sea. Specimens from M. cephalus at both locations were similar. All structures of N. ponticus n. sp. were considerably smaller than those of N. personatus. Two other species of the N. agilis complex are recognized: Neoechinorhynchus agilis (Rudolphi, 1819) sensu stricto from various hosts in the Atlantic and the Mediterranean, and Neoechinorhynchus yamagutii Tkach, Sarabeev & Shvetsova, 2014 from M. cephalus and Planiliza haematocheila in the Pacific, especially the Sea of Japan. Neoechinorhynchus dimorphospinus Amin & Sey, 1996 from marine fish in the Persian Gulf and the Pacific Ocean off Vietnam may be a candidate for membership in the N. agilis complex. X-ray scans of gallium cut and intact hooks of N. personatus and N. ponticus showed differences in the mineral content of hooks with higher sulfur levels in smaller hooks and in hooks from specimens in the Black Sea compared to specimens from the Mediterranean. The relatively high genetic differences between N. ponticus n. sp. and other species of Neoechinorhynchus using a partial 18S rDNA dataset support its independent status. Neoechinorhynchus ponticus n. sp. and N. personatus have a common ancestor with species of Neoechinorhynchus collected from saltwater fish.

The morphology of cystacanths and adults of Profilicollis altmani (Perry, 1942) Van Cleave, 1947 (Polymorphidae) were studied from the Pacific mole crab Emerita analoga (Stimpson) (Crustacea, Hippidae) and Belcher’s gull Larus belcheri (Vigors) (Aves, Laridae), respectively, in Peru. Comparative morphometrics with accounts of other populations of P. altmani from elsewhere off the Pacific and Atlantic coasts of North and South America revealed marked intraspecific population variations. We report scanning electron micrographs (SEM) of new features, not before noted or captured in line drawings by earlier observers. We further present microscope images that reveal internal details not previously reported or possible to see with SEM. Energy dispersive X-ray analysis (EDXA) revealed unusual patterns in the chemistry of proboscis hooks especially the high sulfur and diminished phosphorous and calcium in hook tips and low sulfur and high levels of phosphorous and calcium at mid hooks. The size and shape of all hooks of the cystacanths are reported for the first time. Histopathological studies in L. belcheri from Peru are also included. Cystacanths of P. altmani from California were also analyzed for molecular patterns and compared with other sequences reported from other locations. The molecular data and the analysis of our new sequences of cytochrome oxidase I (COI) showed that haplotypes of P. altmani had low genetic variation; the species is not geographically structured, and within its clade no monophyletic group is formed.

SummaryNew morphometric data, including details of the copulatory system and attachment structures, as well as inner organs are provided for Ancyrocephalus paradoxus Creplin, 1839. Scanning electron microscopy reveals new information of the body shape, position of the cephalic organs’ openings, and structure of anchors, as well as differences in the in anchors’ structure in adults and sub-adults of A. paradoxus. Energy dispersive analysis for X-ray was conducted for the first time for anchors in Monogenea and revealed structural differences between different parts of the anchors in two age groups.

The present study was performed to observe histopathological effects of Oculotrema hippopotami Stunkard, 1924 infection in the eye of Hippopotamus amphibius, as well as to reveal new details of morphology and structural features of this monogenean and its comparison between 2 age stages of the parasite. This was done using both light and scanning electron microscopy, energy dispersive X-ray analysis (EDXA) and histopathology. The presence of a mixture of different generations (adult and sub-adult) in one host individual is common for Oculotrema Stunkard, 1924 in contrast to Polystoma Zeder, 1800. New metrical and graphical information obtained for adults and sub-adults compared with the previous studies. Here we show the presence of genital papillae in adults, metrical data on the distal part of the vas deferens. SEM micrographs of sperm ejaculatory structures and information about the flattened dorsal side of the body provided for the first time. Histopathological changes, such as necrosis and hemorrhage in host tissues as a result of O. hippopotami attachment structures are described. Structural analysis of different body parts of O. hippopotami of both age groups are also included. We show qualitative differences in the presence of hardening ions (S, P, Ca) in attachment structures (oral and haptor suckers) that increase with the age of the worm. The presence of sub-adults and adults on the same host, together with high levels of infection without high pathogenicity may account for Oculotrema being one of the most successful parasites among the Monogenea.

Pallisentis (Pallisentis) nandai Sarkar, 1953 is a freshwater fish parasite restricted to the Indian subcontinent in the Ganga River and its tributaries. It was described from the leaffish, Nandus nandus (Hamilton) from the Ganga River delta at Calcutta. We recovered variant specimens from the same host species from the Ganga near its headwaters at Bijnor about 1500 km away. Our specimens were clearly identifiable as P. nandai but varied considerably from those in the original description, especially in the size of proboscis hooks, receptacle and lemnisci. The original description was incomplete (missing line drawings of female trunk and reproductive system, male trunk, complete proboscis, hooks and hook roots) and inaccurate (proboscis, hooks, receptacle wall), and some measurements were lumped together for both sexes. We provide a complete description and include new morphological information including the first description of para-receptacle structure in the genus Pallisentis Van Cleave, 1928, scanning electron microscopy and microscope images, molecular analysis, and energy dispersive X-ray analysis (EDXA) of hooks and spines of our specimens for the first time. Additional details of proboscis hook roots, trunk spines, micropores and micropore distribution are described. The unique metal composition of hooks (EDXA) demonstrated a considerably high but variable level of sulphur and negligible level of calcium in collar and trunk spines and hook tips, but a higher level of sulphur and calcium at the hook basal arch than at the hook tip and edge. A comparison with the EDXA pattern of another species of Pallisentis, P. İndica Mital & Lal, 1976, were considerably different. The phylogenetic position of P. nandai within Eoacanthocephala was generated to assess the molecular characterization based on 18S and ITS1-5.8S-ITS2 ribosomal DNA sequences. Maximum likelihood and Bayesian inference analyses placed P. nandai in a clade with other Pallisentis species under the family Quadrigyridae. This is the first report based on molecular evidence for P. nandai.