Elucidation of Himasthla leptosoma (Creplin, 1829) Dietz, 1909 (Digenea, Himasthlidae) life cycle with insights into species composition of the north Atlantic Himasthla associated with periwinkles Littorina spp

Trematodes of the genus Himasthla are usual parasites of coastal birds in nearshore ecosystems of northern European seas and the Atlantic coast of North America. Their first intermediate hosts are marine and brackish-water gastropods, while second intermediate hosts are various invertebrates. We analysed sequences of partial 28S rRNA and nad1 genes and the morphology of intramolluscan stages, particularly cercariae of Himasthla spp. parasitizing intertidal molluscs Littorina spp. in the White Sea, the Barents Sea and coasts of North Norway and Iceland. We showed that only three Himasthla spp. are associated with periwinkles in these regions. Intramolluscan stages of H. elongata were found in Littorina littorea, of H. littorinae, in both L. saxatilis and L. obtusata, and of Cercaria littorinae obtusatae, predominantly, in L. obtusata. Other Himasthla spp. previously reported from Littorina spp. in North Atlantic are either synonymous with one of these species or described erroneously. Based on a comparison of newly generated 28S rDNA sequences with GenBank data, rediae and cercariae of C. littorinae obtusatae were identified as belonging to H. leptosoma. Some previously unknown morphological features of young and mature rediae and cercariae of the three Himasthla spp. are described. We provide a key to the rediae and highlight characters important for identification of cercariae. Genetic diversity within the studied species was only partially determined by their specificity to the molluscan host. The nad1 network constructed for H. leptosoma lacked geographical structure, which is explained by a high gene flow owing to highly vagile definitive hosts, shorebirds.

Four marine digenean parasites of Austrolittorina spp. (Gastropoda: Littorinidae) in New Zealand: morphological and molecular data

Littorinid snails are one particular group of gastropods identified as important intermediate hosts for a wide range of digenean parasite species, at least throughout the Northern Hemisphere. However nothing is known of trematode species infecting these snails in the Southern Hemisphere. This study is the first attempt at cataloguing the digenean parasites infecting littorinids in New Zealand. Examination of over 5,000 individuals of two species of the genus Austrolittorina Rosewater, A. cincta Quoy & Gaimard and A. antipodum Philippi, from intertidal rocky shores, revealed infections with four digenean species representative of a diverse range of families: Philophthalmidae Looss, 1899, Notocotylidae Lühe, 1909, Renicolidae Dollfus, 1939 and Microphallidae Ward, 1901. This paper provides detailed morphological descriptions of the cercariae and intramolluscan stages of these parasites. Furthermore, partial sequences of the 28S rRNA gene and the mitochondrial gene cytochrome c oxidase subunit 1 (cox1) for varying numbers of isolates of each species were obtained. Phylogenetic analyses were carried out at the superfamily level and along with the morphological data were used to infer the generic affiliation of the species.

Phenotypic plasticity in the cercarial indices of human and rodent samples ofSchistosoma mansoni(Digenea: Schistosomatidae)

In the epidemiology of schistosomiasis, the cercarial index (CI) has been used for several purposes, including the identification of the species of vertebrate host involved in transmission in a particular setting. The CI of samples of Schistosoma mansoni of human (BH) and rodent (CMO) origin have now been compared, in an attempt to identify morphological markers on cercariae that would indicate whether the eggs from which the cercariae have developed were produced in humans or in rodents. After silver-nitrate impregnation of the cercariae, the CI (and their reaction norms) for the antero-dorsal (AD), antero-lateral (AL) and tail-stem (U) sensory receptors were investigated. The data analysis was based on linear-regression methods, Levene's test for the equality of variances, pooled-variance independent t-tests, and discriminant analysis. The results indicated that CI varied with vertebrate-host origin, that the AD reaction norms were more consistent and plastic than the other reaction norms investigated, that there appeared to be no simple allometric relationship between any of the CI investigated and cercarial body length, and that the BH sample gave larger standard deviations and a higher incidence of mis-classification than the CMO, indicating some developmental instability in the sample of human origin. The relative instability of the BH sample was, however, possibly the result of the experimental procedures. As the parasites used to produce the BH sample had been isolated from humans fairly recently and then routinely maintained in mice, host-induced selection could have affected the sample, altering its CI and their reaction norms. The results of the discriminant analysis indicated that, of the indices investigated, AD was the best morphological marker for distinguishing human and rodent samples of S. mansoni.

The neuro-muscular system in fresh-water furcocercaria from Belarus. I Schistosomatidae

The neuro-muscular system (NMS) in cercariae of the family Schistosomatidae from Belarus was studied with immunocytochemical methods and confocal scanning laser microscopy. The specimens of Bilharziella polonica were compared with Trichobilharzia szidati and Trichobilharzia franki. The patterns of F-actin in the musculature, 5-HT-immunoreactive (IR), FMRFamide-IR neuronal elements and α-tubulin-IR in sensory receptors and nerves were investigated. No indications of structural differences in the musculature, the 5-HT-IR, FMRF-IR neuronal elements and the general distribution of sensory receptors were noticed between cercariae of Trichobilharzia spp. The number of 5-HT-IR neurons in the cercarial bodies is 16. In cercaria B. polonica, the tail musculature is weaker than in Trichobilharzia spp. A detailed schematic picture of the NMS in the tail of Trichobilharzia spp. cercaria is given. The function of NMS elements in the tail is discussed.

The neuro-muscular system in cercaria with different patterns of locomotion

The neuro-muscular system (NMS) of cercariae with different swimming patterns was studied with immunocytochemical methods and confocal scanning laser microscopy. Specimens of the continuously swimming Cercaria parvicaudata, Maritrema subdolum and Himasthla elongata were compared with specimens of the intermittently swimming Cryptocotyle lingua and the attached Podocotyle atomon. The patterns of F-actin in the musculature, 5-HT immunoreactive (-IR), FMRFamide-IR neuronal elements, α-tubulin-IR elements in the nervous and sensory systems and DAPI-stained nuclei were investigated. The general plan of the NMS was similar in all cercariae studied. No major structural differences in the patterns of muscle fibres were observed. However, in the tail of C. lingua, transverse muscle fibres connecting the bands of longitudinal muscles were found. No major structural differences in the 5-HT- or FMRFamide-IR nervous systems were observed. The number of 5-HT-IR neurones in the cercarial bodies varied between 12 and 14. The number and distribution of the α-tubulin-IR processes on the cercarial bodies and tails differed from each other. The relation between the number and structure of the α-tubulin-IR processes and the host finding strategy of the cercariae is discussed. A detailed schematic picture of the NMS in the tails of C. lingua and M. subdolum is presented.

Innervation of cercarial tegumentary receptors investigated by the Sevier-Munger method

The investigation of the sensory nature of tegumentary receptors in platyhelminths remains a challenge due to technical difficulties related to nerve tissue exposure and its experimental handling. Neuromorphological studies have been carried out but few demonstrated the association of these receptors with the nervous system. This paper introduces the Sevier-Munger method as an alternative approach to study the innervation of tegumentary receptors in larval flatworms. Twenty heterophyid cercariae were fixed in hot 5% formalin, with all washes performed in tap and distilled water. They were developed in a solution of ammoniacal silver and 2% formalin under the microscope for 10 min, with preparations shaken gently throughout the procedure. In all specimens, nerve cells stained black against a pale gold background. Fine nerve fibers of the subsurface nerve plexus were observed. These fibers sent distal branches from the plexus to the cercarial tegument. The branches became fine nerve endings, projecting as receptors in the cephalic (5CIV(5), 2CV(2), and 2CV(4)), anterior (4AIL, 3AIIL, 2AIIIL), midbody (1ML, 3MV), posterior (1PIL, 1PIIL, and 1PIIIL), and caudal (2UD) regions of the cercaria. These results indicate that the Sevier-Munger method is useful to demonstrate the association of cercarial tegumentary receptors with the subsurface nerve plexus. They also recommend the use of alternative methods to further investigate flatworm nervous systems. Moreover, there is a pressing urge for a standardized protocol, combining a plethora of methods and techniques. Interdisciplinary collaboration aiming at a better understanding of the function of flatworm nervous systems is particularly encouraged.

Melanoides tuberculatus (Gastropoda: Thiaridae) as intermediate host of Heterophyidae (Trematoda: Digenea) in Rio de Janeiro metropolitan area, Brazil

In the late 1960s, Melanoides tuberculatus snails were introduced in Brazil from North/East Africa and Southeast Asia. The first records of specimens infected with cercariae were registered in Rio de Janeiro State in 2001. The present study reports the occurrence of M. tuberculatus infected with larval trematodes in Rio de Janeiro City. Bottom sediment was collected with dip nets and sieved through 0.25 inch-mesh screening. Snails were transported to the laboratory in vials with stream water, then measured and individually isolated in glass vials with distilled water. They were exposed to artificial light and temperature to induce cercarial emergence. The most actively emerging cercariae were processed by differential staining and silver nitrate impregnation methods. Negative snails were subsequently dissected. Approximately 700 snails were collected. Snail total lengths ranged from 1.2 to 3.3 cm. The prevalence rate was 15.76% although 53.76% of the snails were found infected in one of the sites. Infected snails were infected with rediae and pleurolophocercous cercariae. Cercarial morphology and chaetotaxy were consistent with those of the family Heterophyidae mostly due to the presence of median dorsal and ventral fins on the tail and the absence of CI dorsal sensory receptors.