Oncospheral hook morphogenesis in the davaineid cestode Inermicapsifer madagascariensis (Davaine, 1870) Baer, 1956

The fine structural characteristics of oncospheral hook morphogenesis in the davaineid cestode Inermicapsifer madagascariensis are described. The primordia of the hooks appear in the oncoblasts of embryos in the advanced stage of development, in which there is a greatly reduced number of blastomeres that exhibit a bilaterally symmetrical pattern in their organization.

The hook primordium, adjacent to the invaginated part of the nuclear envelope, is surrounded by an abundance of free ribosomes, mitochondrial aggregations and extended Golgi regions. Simultaneously with its elongation and transformation into a blade, the hook primordium material becomes differentiated to form an electron dense cortex and a less dense, inner, crystal-like core. At the beginning of shank formation, the blade of the hook protrudes outside the oncoblast. The membrane-enclosed point of exit of the blade is surrounded by a cytoplasmic sheath which later forms a circular, septate desmosome.

With oncoblast degeneration, muscle fibres attach directly to the collar and the base of the hook.     

Karyological studies on three strigeid digeneans: Ichthyocotylurus erraticus (Rudolphi, 1809), I. variegatus (Creplin, 1825) and Apatemon gracilis (Rudolphi, 1819)

Previous work has shown that karyology may be a valuable technique for discriminating morphologically similar species. In the present study, chromosome number and morphology were described for three strigeid species, Ichthyocotylurus erraticus (Rudolphi, 1809), I. variegatus (Creplin, 1825) and Apatemon gracilis (Rudolphi, 1819). The results show that these species possess the same diploid number of chromosomes (2n = 20) in somatic cells. The relative length and the position of the centromere were determined, and significant inter-specific differences in the karyotypes are demonstrated, enabling the ready discrimination of I. erraticus and I. variegatus cercariae. A review of known karyotypes of the family Strigeidae suggests that possible routes of evolutionary changes involve pericentric inversions within chromosomes rather than Robertsonian translocations between elements.     

Intraspecific variation in Diplophallus polymorphus (Rudolphi, 1819) (Cestoda: Acoleidae) from avocets and stilts (Recurvirostridae) in North America

Diplopallus polymorphus (Rudolphi, 1819) (Cestoda: Acoleidae), hitherto recorded from avocets Recurvirostra avosetta L. and stilts Himantopus himantopus (L.) (Recurvirostridae) in Europe, Asia and Africa, is reported for the first time as a parasite of Recurvirostra americana Gmelin, 1788 and Himantopus mexicanus (Milller, 1776) in the Pacific, Central and Mississippi migratory flyways of North America. D. polymorphus is redescribed, as it shows great intraspecific variation in the number (20–25) and size (0.087-0.122 mm) of the rostellar hooks and in the position of the cirrus-sac and relation of the external seminal vesicle to the longitudinal excretory vessels. It is found that the intraspecific variations are neither related to host nor to locality of the host. The possible synonymy of D. polymorphus with D. colli Ahern & Schmidt, 1976 and with Himantocestus blanksoni Ukoli, 1965 is discussed.     

Variation in the morphology of adult Apatemon gracilis Rudolphi, 1819 (Digenea: Strigeidae) reared in different avian hosts

Adult Apatemon gracilis (Rudolphi, 1819) were reared experimentally in three different avian hosts: herring gulls Larus argentatus Gmelin, domestic chicks Gallus gallus (L.) and eider ducklings Somateria mollissima (L.). Comparisons of size, body proportions and fecundity were made between these and specimens obtained from a naturally infected goosander Mergus merganser L. The eider duck proved to be a suitable experimental host, rearing adults of comparable size and fecundity to those from the natural host. The growth and development of the parasite in domestic chicks and herring gulls were significantly reduced. Similar conditions are likely to exist in the natural environment and this should be taken into consideration when choosing experimental hosts for use in the laboratory or when identifying species.     

Clinostomum complanatum and Clinostomum marginatum (Rudolphi, 1819) (Digenea: Clinostomidae) are separate species based on differences in ribosomal DNA

Infections by metacercariae of Clinostomum (Leidy, 1856) species adversely affect aquacultured fish and are potentially transmissible to humans. Molecular methodologies are efficient tools, which enable diagnosis of all life-history stages of trematodes in their diverse hosts. The small subunit of ribosomal DNA genes of adults of the Old World Clinostomum complanatum (Rudolphi, 1819) and the New World Clinostomum marginatum (Rudolphi, 1819), obtained from a little egret Egretta garzetta (Linnaeus, 1766) and the great blue heron Ardea herodias (Linnaeus, 1758), respectively, were amplified, sequenced, and aligned. The resulting alignment was used to develop a genetic assay to differentiate between these species.     

Early intrauterine embryonic development of the bothriocephalidean cestode Clestobothrium crassiceps (Rudolphi, 1819), a parasite of the teleost Merluccius merluccius (L., 1758) (Gadiformes: Merlucciidae)

The early intrauterine embryonic development of the bothriocephalidean cestode Clestobothrium crassiceps (Rudolphi, 1819), a parasite of the teleost Merluccius merluccius (L., 1758), was studied by means of light (LM) and transmission electron microscopy (TEM). Contrary to the generic diagnosis given in the CABI Keys to the cestode parasites of vertebrates, the eggs of C. crassiceps, the type of species of Clestobothrium Lühe, 1899, are operculate and embryonated. Our LM and TEM results provide direct evidence that an operculum is present and that the eggs exhibit various stages of intrauterine embryonic development, and in fact represent a good example of early ovoviviparity. The intrauterine eggs of this species are polylecithal and contain numerous vitellocytes, generally ∼ 30, which are pushed to the periphery and remain close to the eggshell, whereas the dividing zygote and later the early embryo remain in the egg centre. During early intrauterine embryonic development, several cleavage divisions take place, which result in the formation of three types of blastomeres, i.e. macro-, meso- and micromeres. These can be readily differentiated at the TEM level, not only by their size, but also by the ultrastructural characteristics of their nuclei and cytoplasmic organelles. The total number of blastomeres in these early embryos, enclosed within the electron-dense eggshells, can be up to ∼ 20 cells of various sizes and characteristics. Mitotic divisions of early blastomeres were frequently observed at both LM and TEM levels. Simultaneously with the mitotic cleavage divisions leading to blastomere multiplication and their rapid differentiation, there is also a deterioration of some blastomeres, mainly micromeres. A similar degeneration of vitellocytes begins even earlier. Both processes show a progressive degeneration of both vitellocytes and micromeres, and are good examples of apoptosis, a process that provides nutritive substances, including lipids, for the developing embryo.     

A taxonomic Study of Species of Bothriocephalus Rudolphi, 1808 (Cestoda: Pseudophyllidea) from Eels in Japan: Morphological and Molecular Evidence for the Occurrence of B. claviceps (Goeze, 1782) and Confirmation of the Validity of B. Japonicus Yamaguti, 1934

A taxonomic study of specimens of Bothriocephalus from eels (Anguilla spp.) in Japan has demonstrated the occurrence of two species, B. claviceps (Goeze, 1782) and B. japonicus Yamaguti, 1934. The former species is a parasite of eels (A. anguilla and A. rostrata) in the Holarctic Region and was recently reported from A. marmorata in Japan. The conspecificity of tapeworms newly found in an eel (A. ? japonica) from Lake Biwa, central Japan, with B. claviceps has been confirmed by the great similarity of their ITS-2 gene sequences (similarity 95.3% and 95.2%). However, the sequences of worms identified as B. claviceps from A. marmorata differed considerably from those of B. claviceps from two populations of A. anguilla from Europe and the above-mentioned one from Japan (similarity 66.3%, 67.1% and 65.1 %, respectively), thus indicating that the former cestodes may have been misidentified. This assumption was confirmed by morphological evaluation of a voucher specimen from A. marmorata. The morphology of this cestode, as well as those from A. japonica from two localities in Japan (Lakes Biwa and Suwa), indicates their conspecificity with B. japonicus. The validity of this taxon has been confirmed on the basis of a re-examination of the type-specimens. The two taxa, B. japonicus and B. claviceps, differ from each other in the shape and length of the scolex (619–730 μm in B. japonicus versus 1,180–2,100 μm in B. claviceps), the relative position of the cirro-vaginal and uterine pores (opposite each other in relation to the median line of the body in B. japonicus versus tandem or slightly offset along the median line in the latter species), and the size of the eggs (41–52 × 28–35 μm in B. japonicus versus 50–70 × 31–43 μm in B. claviceps).

     

Bioecology of the parasites of high altitude homeothermic host-parasite systems. II. Infections by strobilocerci of Hydatigera balaniceps (Hall), H. laticollis (Rudolphi) and H. parva (Baer) in relation to sex, size and weight of Indian house rat

The influence of sex, size and weight of the Indian house rat (Rattus rattus) on concurrent liver infections with Hydatigera balaniceps (Hall), H. laticollis (Rudolphi) and H. parva (Baer) has been discussed. A significant inverse relationship was recorded between cestode infection and rat size. Parasitization index and mean worm burden-host weight ratio decreased with increase in rodent weight.     

Molecular evidence for the synonymy of two species of Apatemon Szidat, 1928, A. gracilis (Rudolphi, 1819) and A. annuligerum (von Nordmann, 1832) (Digenea: Strigeidae) parasitic as metacercariae in British fishes

The current study examined rDNA (internal transcribed spacer regions, ITS1 and ITS2) and cytochrome c oxidase subunit 1 (CO1) sequence data of Apatemon annuligerum (originating from two geographical locations) and A. gracilis metacercariae (originating from four natural piscine hosts) to determine the systematic status of these two strigeid digeneans. With the exception of short repeat motifs, the ITS1 regions sequenced demonstrated no intra- or inter-specific sequence variation. ITS2 sequences were 292 bp and CO1 sequences 366 bp in length and identical for both nominal Apatemon species. These sequence data provide strong evidence that the two species are con-specific and that A. annuligerum should be regarded as a junior synonym of A. gracilis.     

Redescription of Pseudanthobothrium hanseni Baer, 1956 and description of P. purtoni n. sp. (Cestoda: Tetraphyllidea) from different pairs of rajid skate hosts, with comments on the host-specificity of the genus in the Northwest Atlantic

During a parasitological survey of Leucoraja erinacea, L. ocellata, Malacoraja senta and Amblyraja radiata from Passamaquoddy Bay and waters surrounding the West Isles of the Bay of Fundy, NB, Canada, seven species of cestodes were recovered. Examination of these skates revealed the presence of two distinct species of Pseudanthobothrium Baer, 1956: one was retrieved from M. senta and A. radiata, identified as P. hanseni Baer, 1956 and redescribed herein; the other was retrieved from L. erinacea and L. ocellata and differs from previously described species. The new species is described herein as P. purtoni n. sp. on the basis of the degree of apolysis, the maximum width of the strobila, the length of the cirrus-sac and the number of testes. Additionally, the distinctiveness of both species of Pseudanthobothrium is supported by the characterisation of a 643 base-pair nuclear marker, which includes most of the D2 variable region of the large subunit ribosomal DNA (LSU). The recovery of two different tetraphyllidean species, each from two different host species, challenges the oioxeny (strict host-specificity) of echeneibothriine cestodes and can be explained, at least in part, by the similarities in diet and substrate preference within each host pair.