Molecular analysis of an extensive specimen collection of morphologically distinct tapeworms of the genus Caryophyllaeus Gmelin, 1790 (Cestoda: Caryophyllidea), parasites of cyprinid fishes in the Palaearctic Region, brought evidence of host-related plasticity in critical morphological characters widely used for species circumscription and classification of these tapeworms. The results obtained here do not support the traditionally used morphological concept of species-defining characters of the order Caryophyllidea Carus, 1863, especially due to high morphological plasticity of the scolex and the anterior end of the body. Several morphotypes within both Caryophyllaeus laticeps (Pallas, 1781) and Caryophyllaeus brachycollis Janiszewska, 1953 generally corresponding to different hosts and geographical regions, were recognised likely suggesting host- and geography-related intraspecific morphological variability. Genetic data confirmed euryxenous host specificity of both species, most profoundly C. laticeps, but did not support the existence of cryptic species. In fact, some of the fish hosts may harbour both of the congeneric species including several of their respective morphotypes. The pattern of morphological and genetic divergence observed in both cestode species studied indicates a scenario of possible host range extensions and subsequent parasite diversification. If molecular sequence variability and host-related morphological polymorphism are confirmed in other groups of monozoic cestodes, it may complicate species identification and straightforward classification of these parasites.
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.
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.
A comparative study of the scoleces of caryophyllidean tapeworms (Cestoda: Caryophyllidea), parasitic in cypriniform fishes in the Palaearctic Region, was carried out using light and scanning electron microscopy. Three-dimensional pictures of the scoleces of 18 species of caryophyllidean cestodes of the Capingentidae (1 species), Caryophyllaeidae (7) and Lytocestidae (10), and outlines of the scoleces and anterior extent of the testes and vitelline follicles of 19 Palaearctic taxa were documented. Both species of Atractolytocestus Anthony, 1957 possess a bulboacuminate scolex, whereas species of Archigetes Leuckart, 1876 have fossate scoleces of the bothrioloculodiscate type, with loculi, bothrium-like depressions and an apical disc. Breviscolex orientalis Kulakovskaya, 1962, the only member of the Capingentidae, has a cuneiform scolex, as do both taxa of the lytocestid genus Caryophyllaeides Nybelin, 1922. The scoleces of two species of Caryophyllaeus Gmelin, 1790 are flabellate, whereas that of the congeneric C. fimbriceps Annenkova-Chlopina, 1919 is cuneicrispitate. Khawia Hsü, 1935, the most specious Palaearctic genus, with seven taxa that we consider to be valid, has the highest diversity in scolex morphology: semi-bulbate, flabellate, cuneiform, cuneifimbriate, truncated cuneiform-flabellate and festoon-like. Species of Monobothrium Nybelin, 1922 have either a digitiform scolex with widened posterior part or cuneiform, with lateral auricular extensions. Paracaryophyllaeus gotoi (Motomura, 1927) is characteristic in its possessing a bulbate scolex, whereas Paraglaridacris limnodrili (Yamaguti, 1934) has a fossate scolex of the bulboloculate type with bothrium-like depressions and feebly developed lateral loculi. Anterior extent of the testes and vitelline follicles and their mutual position show a somewhat higher variability than scolex shape, with intraspecific variation in some taxa, such as Atractolytocestus sagittatus (Kulakovskaya et Akhmerov, 1965), B. orientalis, Khawia armeniaca (Cholodkovsky, 1915) and K. sinensis Hsü, 1935. Based on scolex morphology and relative position of the anterior testes and vitelline follicles, a key is provided to facilitate the routine identification of 20 Palaearctic caryophyllidean taxa.
The ultrastructure and chemical composition of the proboscis hooks and surrounding tegument of Acanthocephalus lucii (Müller, 1776), a parasite of European perch, Perca fluviatilis Linnaeus, were examined using scanning (SEM) and transmission (TEM) electron microscopy and X-ray microanalysis (EDXA). The blade of middle hooks consists of three layers: an outer homogeneous layer, an inner heterogeneous layer and a central core. TEM observation revealed the presence of hollow tubes, which spaced the central core; fibrous inner hook layer surrounded by an electron-dense margin and the basal tegumental layer filled with electron-dense bodies and outer layer. We found for the first time that the so-called ''epidermal covering'' surrounding of the exposed hook blade (outer hook layer) is a modified striped portion of the tegumental layer and there are no special contact sites between these two morphologically different structures, i.e. striped layer of the syncytial tegument and following proper outer hook layer, which is a homogeneous, moderately electron-dense layer of ~0.3 µm in thickness. The hook root is embedded into subtegumental fibrous layer. X-ray microanalysis of both the surface and internal parts of A. lucii hooks demonstrated the presence of calcium, magnesium, phosphorus and sulphur. The highest concentration of sulphur was recorded at the tip of hooks, whereas the middle part of the hooks was most rich in calcium, phosphorus and magnesium. The proximal part of the hooks contained lower concentrations of sulphur, calcium and phosphorus. In the proboscis tegument, only two elements, calcium and silicon, were found. The differences observed in the chemical composition of the hook ''epidermal covering'' and the proboscis tegument support our ultrastructural findings that the hook tegumental covering is a modified structure compared with that of the general proboscis tegument.