Observations on the fine structure of the cercaria of Notocotylus attenuatus and formation of the cyst wall of the metacercaria

Musculature arrangement and locomotion in notocotylid cercariae (Digenea: Notocotylidae) from mud snail Ecrobia ventrosa (Montagu, 1803)

Cercariae of digenean family Notocotylidae are characterized by a set of morphological traits which make them easily distinguishable from any other. One of the key features is absence of ventral sucker. This affects basic ways of locomotion and attachment. To understand how these functions are fulfilled we studied musculature arrangement in cercariae of two species by means of fluorescent-phalloidin staining and confocal microscopy. We used Cercaria Notocotylidae sp. No. 11 and 12 Deblock, 1980 from mud snails Ecrobia (=Hydrobia) ventrosa. Information on gross morphology (especially body-tail junction) and basic behavioural patterns of these cercariae is also updated. Major special features of musculature are associated with the ventral concavity: extreme development of dorsoventral muscle fibres and formation of annular arrangement of longitudinal muscle fibres on the ventral side. Additional body-wall and internal muscle bundles in the anterior region are also specific for notocotylid cercariae and seem to play important role in twisting movements during substratum testing. Musculature of dorsal adhesive pockets, oral sucker and tail is also described. These results are discussed in relation to observed locomotory patterns.

The attachment of cercariae of an ectoparasitic digenean,Transversotrema patialensis, to the fish host: behavioural and ultrastructural aspects

The behaviour which enables the cercariae of the ectoparasitic digenean,Transversotrema patialensis, to establish themselves on the surface of their fish hosts has been described experimentally using anaesthetized fish. Specialized regions of the cercarial tail, the arm processes, seem to be adapted for both specific recognition of, and rapid attachment to, the outer surface of a fish. Each arm process bears an array of nine ciliary sensory structures, the mammiform receptors, which have been tentatively identified as contact chemoreceptor organs involved in host recognition. Also present on each arm is an adhesive pad that mediates the initial attachment to the host. It is a differentiated region of the distal cytoplasm of the epidermal syncytium which invests the whole arm process. The cytoplasm of the pad region contains membrane-bounded adhesive granules, the contents of which are released during activation of the pad.

The structure and possible function of the ventral papillae of Notocotylus triserialis Diesing, 1839

Notocotylus triserialis bears three rows of eversible papillae on its ventral surface. These papillae, which in living worms are firmly applied to the host mucosa, contain numerous pyriform cells. Histochemical tests indicate the presence, within the papillar cells, of protein, lipid, haemoglobin and esterase, and the absence of carbohydrate, acid mucopolysaccharide, RNA, haemosiderin and acid and alkaline phosphatase. Transmission electron microscopy shows the tegument of the papillae to be similar to the non-papillar ventral tegument. The pyriform cells contain many mitochondria with numerous cristae. A mechanism is proposed whereby the musculature of the worm effects the retraction and eversion of the ventral papillae.

A comparative ultrastructural and histochemical study of the metacercarial cyst walls of four species of Paragonimus (Troglotrematidae: Trematoda)

The metacercarial cyst walls of Paragonimus westermani, P. miyazakii, P. ohirai, and P. iloktsuenensis were examined using ultrastructural and histochemical techniques. The cyst walls of P. westermani, P. miyazakii, and P. ohirai were found to have five distinct layers, whereas the wall of P. iloktsuenensis had only two. The so-called outer cyst wall recognized on light microscopy by Miyazaki (1961) was composed of layers I-III and the so-called inner cyst wall comprised layers IV and V. The outermost layer (I) consisted of collagen fibers and probably originated from the host. Layer III detached easily from layer IV on removal of the cysts from the host tissues. Layer IV was composed of proteoglycans, and layer V consisted of protein alone. A regular hexagonal pattern in layer V appeared to be characteristic of P. westermani. Although the basic morphological patterns observed in the layers constituting the cyst walls were similar in all species examined, the thickness of each layer was apparently different. This characteristic seems to be a suitable criterion for the identification of metacercarial cysts of Paragonimus species.

The ultrastructural characterization of the tegument of Clonorchis sinensis (Cobbold, 1875) cercaria

The tegumental ultrastructure of the cercaria of the liver fluke, Clonorchis sinensis (Cobbold, 1875), was studied by scanning and transmission electron microscopy. The body surface is almost encircled by many rows of regularly arranged spines. The tegumental syncytium of the body contains many rod-shaped dense granules and central electron-lucent bodies, neither of which are present in the tail tegument. There are four rows of hooked teeth and modified spines on the oral cone. These teeth are differentiated morphologically and probably functionally from the other body spines. Disc-shaped papillae with long or short cilia are distributed on the body in a bilaterally symmetrical pattern dorsally and ventrally. There are 30 to 37 papillae with much longer cilia laterally. Four pairs of papillae were found on the tail. From their structure and location these papillae appear to have a mainly tango- or rheoreceptive function. Another type of sheathed papillae is situated around the oral sucker. The cuticular tegument is expanded laterally at the base of the tail, forming a characteristic sac-like structure.