Examination of 4055 molluscs of 10 species from cenotes (= sinkholes) and other freshwater bodies in the Yucatan Peninsula, Mexico revealed the presence of-larval stages of 13 trematodes. The following species were found: Echinochasmus leopoldinae Scholz, Ditrich et Vargas-Vázquez, 1996, E. macrocaudatus Ditrich, Scholz et Vargas-Vázquez, 1996 (Echi-nostomatidae), Saccocoelioides sp. (? sogandaresi Lumsden, 1963) (Haploporidae), Crassicutis cichlasomae Manter, 1936, pleurolophocercous ophthalmocercaria sp. (Homalometridae), Ascocotyle (Ascocotyle) sp., Ascocotyle (Phagicola) nana Ransom, 1920 (Heterophyidae), Oligogonotylus manieri Watson, 1976 (Cryptogonimidae), Genarchella astyanactis (Watson, 1976) (Derogenidae), xiphidiocercariae sp. 1, 2 and 3 (Lecithodendriidae?), and furcocercaria gen. sp. (Fellodistomidae). The life-cycle of the derogenid Genarchella astyanactis was studied for the first time. It was found that it differs from that of G. genarchella: the first intermediate host, Pyrgophorus coronatus (Pfeiffer, 1839), released cystophorous furcocercariae of G. astyanactis that developed, after ingestion by the second intermediate host, copepods (experimentally Mesocyclops chaci Fiers, Reid, Ilife et Suárez-Morales, 1996), into metacercariae resembling by their morphology juvenile trematodes found in the stomach of Aslya-nax fasciatus. No progenetic cercariae (metacercariae) found in G. genarchella were observed in the life-cycle of G. astyanactis. Rediae and cystophorous furcocercariae were recovered from naturally infected snails and snails experimentally kept in contact with eggs from the uterus of G. astyanactis adults.
During a survey of the parasites of freshwater fishes from cenotes (sinkholes) of the Yucatan Peninsula the following species of monogeneans were found on cichlid, pimelodid, characid and poeciliid fishes: Sciadicleithrum mexicanum Kritsky, Vidal-Martinez et Rodriguez-Canul, 1994 from C.ichlasoma urophthalmus (Giinther) (type host), Cichlasoma friedrichsthali (Heckel), Cichlasoma octofasciatum (Regan), and Cichlasoma synspilum Hubbs, all new host records; Sciadicleithrum meekii Mcndoza-Franco, Scholz et Vidal-Martinez, 1997 from Cichlasoma meeki (Brind); Urocleidoides chavarriai (Price, 1938) and Urocleidoides travassosi (Price, 1938) from Rhamdia guatemalensis (Günther); Urocleidoides costaricensis (Price et Bussing, 1967), Urocleidoides heteroancistrium (Price et Bussing, 1968), Urocleidoides anops Kritsky et Thatcher, 1974, Anacanthocotyle anacanthocolyle Kritsky et Fritts, 1970, and Gyrodaclylus neotropicalis Kritsky et Fritts, 1970 from Aslyanax fasciatus; and Gyrodactylus sp. from Gambusia yucatana Regan. Urocleidoides chavarriai, U. travassosi, U. costaricensis, U. heteroancistrium, U. anops, Anacanthocotyle anacanthocotyle and Gyrodactylus neotropicalis are reported from North America (Mexico) for the first time. These findings support the idea about the dispersion of freshwater fishes and their monogenean parasites from South America through Central America to southeastern Mexico, following the emergence of the Panamanian isthmus between 2 and 5 million years ago.
From May 1993 to April 1995, the seasonal occurrence of metacestodes of Neogryporhynchus cheilancristrotus (Wedl, 1855) (Cyclophyllidea: Dilepididae) in its second intermediate host, the blue bream Abramis ballerus (L.) was studied monthly in the Oder River on the borders of Germany and Poland. Based on the parasite specimens found, detailed data on their morphometries are presented. The metacestodes occurred in the blue bream intestine throughout the year (overall prevalence 27% and intensity 1-56 (mean 4.8) metacestodes per infected fish). Increased prevalences and mean intensities of infection were noted from March to June and November to December indicating that spring, late autumn and early winter are the main periods of new infections.
Specimens of three little-known species of Rhabdochona (Nematoda: Rhabdochonidae) were collected during occasional examinations of some freshwater fishes in India: R. (Rhabdochona) hellichi turkestanica (Skryabin, 1917) in Schizothorax sp. (Cyprinidae, Cypriniformes) from the Lodhomakhola and Rangit Rivers, West Bengal and Sikkim, respectively; R. (R.) hospeti Thapar, 1950 in Tor sp. (Cyprinidae) from the Rangit River; and R. (Globochona) mazeedi Prasad et Sahay, 1965 in Clupisoma garua (Hamilton) (Schilbeidae, Siluriformes) from the Farakka Dam Lake, West Bengal. Their detailed light and electron microscopical studies revealed some taxonomically important, previously not observed features and made possible their redescription. Fourth-stage larvae of R. hospeti are described for the first time. Rhabdochona hellichi turkestanica (syns. R. denudata filamentosa Bykhovskaya-Pavlovskaya, 1936, R. kashmirensis Thapar, 1950, R. schizothoracis Siddiqi et Khattak, 1984) is proposed as a subspecies, differing from the nominotypical subspecies R. hellichi hellichi (Šrámek, 1901) mainly in the shape of the distal end of the left spicule, molecular data and geographical distribution. Rhabdochona moraveci Katoch et Kalia, 1991 (a homonym to R. moraveci Duggal et Kaur, 1987) is renamed R. indica nom. n. The following six species are considered new junior synonyms of R. hospeti: Comephronema [sic] mackiewiczi Malhotra et Rautela, 1984, Rhabdochona moraveci Duggal et Kaur, 1987, R. bifidum Kakar et Bilqees, 2007, R. uvaginus Kakar et Bilqees, 2007, R. bolani Kakar, Bilqees et Ahmad, 2008 and R. cephalodiverticula Kakar, Bilqees et Ahmad, 2008. Rhabdochona edentati Paul et Majumdar, 1994 is considered a species incertae sedis.
Specimens of the nematode genus Rhabdochona Railliet, 1916 (Rhabdochonidae) were collected during helminthological examination of four species of cyprinid fishes in two rivers of the Amur River basin in the Russian Far East (Primorsky Region) in June 2011. Detailed light microscopical (LM) and scanning electron microscopical (SEM) examinations (the latter used for the first time for the reported nematode species) of the available material revealed the presence of three inadequately described nominal species of this genus: R. (Rhabdochona) denudata (Dujardin, 1845) from the spotted steed Hemibarbus maculatus Bleeker (Gobioninae), and R. (Rhabdochona) longispicula Belous in Roytman, 1963 and R. (Globochonoides) coronacauda Belous, 1965 from Culter alburnus Basilewsky (Cultrinae) in the Ilistaya River. Detailed morphological study of these worms, especially SEM examination, made it possible to reveal some previously unreported morphological features (e.g., the presence of sublabia or the character of ventral precloacal ridges) and to confirm other taxonomically important characters such as the shape of deirids, number of anterior prostomal teeth, number and situation of lateral preanal and postanal papillae or the detailed structure of the crown-like formation on the female tail tip in R. coronacauda. Unidentifiable Rhabdochona (Rhabdochona) gravid females were recorded from the humpback Chanodichthys dabryi (Bleeker) (Cultrinae) in the Ilistaya River and from the Amur minnow Rhynchocypris lagowskii (Dybowski) (Leuciscinae) in the Komissarovka River.
Two fish cestodes, the little-known Eubothrium fragile (Rudolphi, 1802) and E. rugosum (Batsch, 1786), the type species of the genus Eubothrium Nybelin, 1922, are redescribed on the basis of new material from twaite shad, Alosa fallax (Lacépède, 1803), from England and burbot, Lota lota (Linnaeus, 1758), from Russia, respectively. The tapeworms are compared with two other species of the genus, E. crassum (Bloch, 1779) and E. salvelini (Schrank, 1790), common parasites of salmonid fish in the Holarctic. The most notable differential characters are the size and the shape of the scolex (smaller and oval in E. fragile), the shape of the apical disc (four or more indentations in E. crassum), the number and size of the testes (the largest and least numerous in E. rugosum), and the position and size of the vitelline follicles (almost entirely cortical in distribution in E. fragile and E. crassum versus largely medullary in E. rugosum and E. salvelini). A comparison of species has also shown the morphological similarity of the freshwater species (E. rugosum and E. salvelini) on one hand and those of marine origin, E. fragile and E. crassum, on the other, with the latter species occurring also in fresh waters. A key to the identification of the species studied is also provided.
Proteocephalus macrophallus (Diesing, 1850), considered by several authors as species inquireruia, was recently found in Cichla ocellaris in Venezuela. This material is compared with voucher specimens from the same host (C. ocellaris) from Brazil, identified and redescribed as P. macrophallus by Woodland (1933). The specific status of P. macrophallus is confirmed. This species is characterized by: 1 ) the shape of the body, which is wide and short, 2) the absence of a neck, 3) the distribution of the vitelline follicles, which converge posteriorly to the ovarian lobes, and 4) the structure of the uterus, which is evacuated in the last proglottides and transformed to thick-walled diverticles apparently separated each from other. A neotype is designated.
Monozoic cestodes of the genus Khawia Hsü, 1935 (Caryophyllidea: Lytocestidae), parasites of cyprinid fish in Europe, Asia, Africa and North America, are revised on the basis of taxonomic evaluation of extensive materials, including recently collected specimens of most species. This evaluation has made it possible to critically assess the validity of all 17 nominal species of the genus and to provide redescriptions of the following seven species considered to be valid: Khawia sinensis Hsü, 1935 (type species); K. armeniaca (Cholodkovsky, 1915); K. baltica Szidat, 1941; K. japonensis (Yamaguti, 1934); K. parva (Zmeev, 1936); K. rossittensis (Szidat, 1937); and K. saurogobii Xi, Oros, Wang, Wu, Gao et Nie, 2009. Several new synonyms are proposed: Khawia barbi Rahemo et Mohammad, 2002 and K. lutei Al-Kalak et Rahemo, 2003 are synonymized with K. armeniaca; K. coregoni Kritscher, 1990 with Caryophyllaeus laticeps (Pallas, 1781) (family Caryophyllaeidae); K. cyprini Li, 1964 and K. iowensis Calentine et Ulmer, 1961 with K. japonensis; K. dubia (Szidat, 1937) (syn. Bothrioscolex dubius Szidat, 1937) with K. rossittensis; and Tsengia neimongkuensis Li, 1964 and T. xiamenensis Liu, Yang et Lin, 1995 with K. sinensis. Khawia prussica (Szidat, 1937) (syn. Bothrioscolex prussicus Szidat, 1937) is considered to be species incertae sedis, but its morphology indicates it may belong to Caryophyllaeus Gmelin, 1790 (Caryophyllaeidae). The molecular analysis of all seven valid species, based on comparison of sequences of two nuclear ribosomal and two mitochondrial genes, has shown that the species form three major groups clustered according to their fish hosts. Five species from common and crucian carp and goldfish were grouped together, whereas K. armeniaca from barbels (Barbinae) and K. baltica from tench (Tinca) formed separate clades. In contrast, geographical distribution does not seem to play a crucial role in grouping of individual taxa. A phylogenetic tree based on morphological characters was incongruent with that inferred from molecular data, which indicates that some morphological traits may be homoplastic. A key to identification of all species of Khawia based on morphological characteristics is provided.