The structure and composition of the cyst wall of the metacercaria of Cloacitrema narrabeenensis (Howell & Bearup, 1967) (Digenea: Philophthalmidae).

The mstacercarial cyst of Cloacitrema narrabeenensis which is formed in the open is composed of four layers: an outermost layer of acid mucopolysaccharide, a layer of protein which is presumed to be tanned, a layer of neutral mucopolysaccharide and an innermost layer of keratinized protein. The two layers which together form the outer cyst wall can be split off by slight pressure from the two remaining layers which together form the inner cyst wall. In the centre of the ventral side of the inner cyst wall, the keratinized layer is incomplete and this ventral plug region is composed of neutral mucopolysaccharide. The cyst wall is therefore very similar to that of Fasciola hepatica, the main difference being that the order of the two layers of the outer cyst is reversed. General evolutionary and functional relationships of metacercarial cysts are discussed.     

Schistosoma mansoni: changes in the outer membrane of the tegument during development from cercaria to adult worm

Hockley D. J. and McLaren D. J. 1973. Schistosoma mansoni: changes in the outer membrane of the tegument during development from cercaria to adult worm. International Journal for Parasitology3: 13–25. The tegumental outer membrane of the cercaria is trilaminate: the adult worm, however, has a seven-layered membrane. Formation of the heptalaminate membrane commences immediately after the cercaria has penetrated the vertebrate host: multilaminate membrane-bounded vacuoles are passed from subtegumental cells into the tegument where they enlarge, join to the outer membrane and open to the exterior. The heptalaminate limiting membrane of the vacuole thus becomes the outer membrane of the tegument. At the same time the original trilaminate tegumental membrane is formed into microvilli which are cast off and thus the cercarial outer membrane is lost. Schistosomula usually have a heptalaminate outer membrane within three hours of penetration. After this time the large vacuoles are replaced by smaller membraneous bodies which presumably contribute to the outer membrane during growth of the schistosomulum. The membraneous bodies are also present in the tegument of the adult worms and there is some evidence that the outer membrane is continually renewed.     

The formation of the cyst wall of the metacercaria of Fasciola hepatica L.

Summary The several concentric layers of the cyst wall of Fasciola hepatica are formed from precursors synthesised in the cystogenic cells of the cercaria during its development in the redia. A cinematographic analysis shows that the separate components are released in succession during encystment.The outer portion of the wall consists of two layers: a tanned protein and a carbohydrate-protein complex. The granular precursors of these are formed in separate groups of cells and migrate from these cells into the superficial epithelium (embryonic epithelium) during development. They are released to form the outer wall by the bursting of the embryonic epithelium at the beginning of encystment. This process is rapid and is completed in a few minutes.A pause follows the separation of the outer wall during which a further polysaccharide layer is released and the cells, which contain the rod-like scrolls of sheets of the laminated component of the inner wall, migrate from within the cercaria through gaps in the superficial musculature on to the cercarial surface to form a new epithelium replacing that previously shed.The cercaria now begins a series of complex oscillatory movements within the enveloping outer cyst wall during which the scrolls are secreted into the space underneath the outer wall, unroll and are compacted by the animal's movements into the lamellar inner wall.The rodlets are enclosed in vacuoles and their secretion is effected by the fusion of the vacuolar membrane with the plasma membrane without destroying the integrity of the cells, which remain to constitute the epithelium of the juvenile fluke when this emerges later.     

Metacercarial cyst formation in vitro of Echinostoma paraensei

Cercariae of Echinostoma paraensei Lie and Basch 1968 encysted normally in the presence of Biomphalaria glabrata embryo (Bge) cells in culture, partially in culture conditioned medium, and not at all in fresh culture medium alone. At the ultrastructural level the cyst is composed of 2 well defined regions. The outer cyst wall (OCW) is particulate to fibrous in nature, formed from secretory granules released from the cercarial tegument. Membranous scrolls or rodlets secreted from the subtegumental cystogenous gland cells are then added to this layer, forming the inner cyst wall (ICW). After 24 hr the cultured cyst is enclosed by a thin cellular capsule similar to that found around cysts in the snail host. The capsule also contains collagen fibers, not found elsewhere in Bge cell cultures.     

The fine structure of the cystogenic cells of the cercaria of Fasciola hepatica L.

Summary The wall of the cyst of the metacercaria of the liver fluke (Fasciola hepatica L). is composed of four layers: an external tanned protein, two layers giving reactions of proteins and polysaccharides and an internal, finely laminated layer of keratinized protein. Each of the precursors of these layers is synthesised in a distinct kind of cystogenic cell in the cercaria, while it is still within the redia in the intermediate host, a snail.The cells forming the protein precursors are similar in cytoplasmic structures to secretory cells such as those of the exocrine pancreas. The cells producing protein and polysaccharides resemble mucinogenic cells.The keratin precursor is a rodlet formed by the rolling of a sheet into a scroll and all stages of this process can be recognised in the synthesising cells in the early cercaria.     

The life cycle of Cloacitrema michiganensis McIntosh, 1938 (Trematoda: Philophthalmidae)

Experimental infections of Cloacitrema michiganensis were established in chicks by inoculation per cloaca with excysted metacercariae. Ovigerous adults were present 20 days later with eggs containing ocellate miracidia after 21 days. The eggs hatch in utero; the miracidium contains a fully developed redia. Rediae of 2 size groups were present in the digestive gland of the brackish-water snail, Cerithidea californica. Megalurous cercariae are released and encyst on submerged objects. The stages of C. michiganensis resembled those of Parorchis acanthus, a philophthalmid also infecting C. californica, except for differences in the epidermal plate count of their miracidia and in their cercarial stage which was larger in P. acanthus and had a spinuous tegument with a collar of spines.     

The development of the primitive epithelium and true tegument in the cercaria of Schistosoma mansoni.

The formation of the final cercarial tegument of Schistosoma mansoni is preceded by that of a so-called primitive epithelium. The primitive epithelium is derived from the tegument of the daughter sporocyst. The final cercarial tegument is formed from peripherally located somatic cells of the cercarial embryo, which expand and coalesce beneath the primitive epithelium. The primitive epithelium degenerates and disappears. The ultrastructure of both epithelia in the course of the development of the cercaria is described in detail. Possible functions are discussed.     

Ultrastructure of three types of sense receptors of larval Austramphilina elongata (Amphilinidea)

Ultrastructure of three types of sense receptors of larval Austramphilina elongata (Amphilinidea). International Journal for Parasitology16: 245–251. The ultrastructure of three sense receptors is described. The first is the ending of an anterior dendrite which penetrates deeply into the epidermis and is surrounded by an invagination into the epidermis of the tegument, basal lamina and a thick layer of underlying fibrous matrix, and contains electrondense collars, a basal body and a short ciliary rootlet; it does not reach the surface and is without a cilium. The second is a dendrite which penetrates through the tegument and epidermis and does not contain electron-dense collars, a basal body or a cilium; it forms a free ending on the surface. The third is a nerve ending in the epidermis without electron-dense collars or a basal body, with microvilli-like structures (rhabdomere) and flanked by a densely granular (pigment?) body on one side; it is interpreted as a simple photoreceptor. Diagrams of six sense receptors previously described are given, and the distribution of the receptors in the larva is discussed.     

Ultrastructure of the daughter sporocyst and developing cercaria of Schistosoma japonicum in experimentally infected snails, Oncomelania hupensis hupensis

Ultrastructure of daughter sporocysts and cercariae of Schistosoma japonicum were studied 2 and 4 months after infection of Oncomelania hupensis hupensis. The body walls of daughter sporocysts are similar at all infectious stages. They consist of an external syncytial tegument on a basement membrane, and an internal cellular subtegument surrounding a body cavity containing developing cercariae. The cercariae embryos develop 2 months after infection from germinal balls in the brood chamber of the daughter sporocyst. They are at first enveloped by a primitive epithelium rising from the daughter sporocyst. Four months after infection, the cercariae were almost fully developed and the primitive epithelium had degenerated. The body wall of the cercaria consists of a thin tegument covered by a surface coat of fibrous material and connected to the subtegumental cells by cytoplasmic processes. The matrix of the tegument contains numerous dense bodies, vacuoles, and spines. Two types of sensory structures - uniciliated and multiciliated - are found at the anterior tip of the cercaria. There are five pairs of penetration gland cells of two distinct types differentiated by the morphology of secretory granules. Flame cells are found in both daughter sporocysts and in cercariae. The cilia of the flame cells are characterized by the typical 9 and 2 cilium pattern.     

A histochemical study of the secretory gland cells of Cercaria shikokuensis and their role during development from cercaria to metacercaria.

The roles of secretory glands during the developmental process from an immature cercaria to a metacercaria in Cercaria shikokuensis were studied. Four types of secretory cells were identified in this species. On maturation of the cercaria in redia, the products of ventral gland cells and mucoid gland cells formed a thick surface coat on the mature cercaria, and the products of cephalic gland cells also formed a thin cover on the surface coat. In the process leading to the formation of a metacercaria, the surface coat constituted the outer layer of the cyst, mucoid gland cells secreted mucous substances inside the wall, and then cystogenous gland cells discharged their products to the inner wall. The cyst wall was composed of four layers, and it was thought that the outermost surface layer helped the cyst wall to adhere to the matrix and the intermediate layers helped to put together outer and inner walls.     

Stereoscan studies of rediae, cercariae, cysts, excysted metacercariae and migratory stages of Fasciola hepatica

The external surface of the redial body of Fasciola hepatica is provided with microvillus-like projections or short lamellae, and short cilium-like structures are common anteriorly. The anterior part of the cercarial body possesses a pattern of regularly arranged small depressions each containing a spine. Both long and short cilium-like structures occur anteriorly. The tail is spineless and provided with dorsolateral folds. The outer cyst wall is formed by granules secreted from the tegument all over the body apart from the ventral sucker. Most granules transform into fibrillae which form the thick outer spongy layer. The precursor of the inner cyst wall is at the beginning closely attached to the metacercarial surface, but later the membrane-like cyst wall extends, and when fully formed the metacercaria lies free in the flattened circular inner cyst. The ventral plug is formed by the ventral sucker. The tegument of newly excysted metacercariae is provided with simple pointed spines, but later during migration in the mouse the spines become flattened and multipointed. Very young migratory stages may be attached with host cells.     

Schistosoma mansoni: topochemical features of cercariae, schistosomula, and adults

The teguments of developing and mature cercariae, recently transformed, and 1-wk-old schistosomula and adult worms were examined for the ultrastructural location of macromolecular carbohydrates and polyelectrolytes. The surface of mature cercariae within sporocysts and cercariae released from the snail is covered by a filamentous coat which reacts with cytochemical reagents for the demonstration of vicinal glycols, but neither the coat nor the surface of the tegument plasmalemma binds cationic colloidal iron at low pH.Upon penetrating mammalian skin, the cercaria sheds its surface coat; the tegument surface of newly transformed schistosomula, older schistosomula and adult worms stains en bloc with acidic colloidal iron, as does the tegument plasmalemma of mature cercariae if the overlying filamentous coat is first removed by physicochemical means. The cercarial coat thus serves to mask anionic groups at the surface of the tegument plasmalemma which become functionally exposed after penetration of the mammalian host. The distribution of colloidal iron binding sites coincides with those for the carbohydrate-complexing phytohemmagglutnin, concanavalin A, which suggests that these membrane-fixed anions are acid mucopolysaccharides, glycoproteins or glycolipids. Carbohydrate-containing material was also localized within membrane-bound vesicles of the tegument matrix and perikarya of developing cercariae and postcercarial schistosomes, suggesting that surface mucosubstances contributing to the tegument glycocalyx of these worms are elaborated, at least in part, by the tegument itself.     

Phylogenetic position and morphology of Raphidiophrys elongata sp. nov. (Haptista: Centroplasthelida) with notes on cyst wall structure and evolution

The majority of centrohelids bear external coverings consisting of organic spicules or siliceous scales. Cyst coverings are usually reinforced with additional layers of modified scales. The cyst wall of Raphidiophrys heterophryoidea has an unusual and complex structure. It consists of three different types of scales and includes the mosaic scale layer not known in other centrohelids. During excystment, the cyst wall fragments along the sutures of the mosaic layer. For other Raphidiophrys species, cyst coverings are not studied. The present paper describes a new Raphidiophrys species, R. elongata, belonging to the NC7 environmental clade. Trophozoites bore thin plate scales with reduced upper plate. Under starvation, cysts emerged in clonal cultures. Cyst coverings of R. elongata and R. heterophryoidea were studied in comparison with the use of FIB-SEM. Cyst wall of R. elongata was significantly thinner than in R. heterophryoidea and was formed with 3–5 layers of uniform overlapping scales. No mosaic scale layer was present. During excystment, trophozoite exited cyst shell through random fissure. Possible evolutionary events and driving forces behind the complication of cyst wall within Raphidiophrys were discussed.     

The cercarial tail in Proterometra macrostoma (Digenea: Azygiidae): permeability and fine structure of the tegument

Permeability of the cercarial tail in Proterometra macrostoma was examined in vitro with 1 mM 3H-glucose, which tails absorb by diffusion alone. Naturally emerged cercariae (bodies withdrawn into tails) were permeable, but they rapidly (3 min) equilibrated with glucose in the bathing medium and maintained steady state for 4 hr. Metabolism of absorbed glucose was not detectable until after 90 min, and radioactivity in bodies dissected from tails after 4 hr was negligible. On the basis of cercarial water content (90% of total weight) and absorbed isotope at steady state, the calculated volume of the equilibrating compartment was 4% of an intact cercaria. This value correlated well with that of the tegument (3-5%), which was 1-2 microm thick as seen by transmission electron microscopy. A continuous, electron-dense basal membrane/lamina separated the tegument from subtegument. We conclude that the glycocalyx and external plasma membrane are freely permeable, whereas the basal membrane is the barrier that effectively isolated the subtegument from exogenous glucose. The basal membrane also may be the primary structure that protects the subtegument and cercarial body from effects of osmotic stress.     

长尾蚴吸虫幼虫在菲律宾蛤仔的寄生部位及其组织化学的研究

本文报道长尾蚴吸虫幼虫在菲律宾蛤仔的寄生部位及其组织化学的研究,长尾蚴吸虫幼虫主要寄生于哈仔的生殖腺组织中,仅少部分进入生殖腺附近的消化腺,鳃等。受感染严重的蛤仔,其生殖腺的滤泡等组织被虫体占满并被耗尽,长尾蚴吸虫子胞蚴的胞壁及尾蚴的皮导主要含碱性蛋白质和粘蛋白,子胞蚴的胚球,尾蚴的吸盘,生殖原基,单细胞腺体主要ＤＮＡ阳性物质,排泄囊含丰富的碱性蛋白质;尾蚴体的中部含有呈颗粒团的粘蛋白和抗淀粉酶的     

Differentiation of the tegument and associated structures in Diphyllobothrium dendriticum Nitsch (1824) (Cestoda: Pseudophyllidea). An electron microscopical study

Grammeltvedt Anne-François 1973. Differentiation of the tegument and associated structures in Diphyllobothrium dendriticum Nitsch 1824 (Cestoda : Pseudophyllidea). An electron microscopical study. International Journal for Parasitology3: 321–327. The differentiation of the tegument and associated structures of the coracidium, procercoid, plerocercoid and adult is described. The embryophore is composed of four zones and is covered by a fibrous layer resembling a glycocalyx. The oncospheral plasma membrane is extensively folded. A typical cestode tegument, with a distal and perinuclear cytoplasm, is probably already existing in the coracidium. The formation of the microvilli starts after about three days in the copepod host. In young procercoids ribosomes and Golgi complexes were observed in the distal cytoplasm. These organelles disappear at later stages. The infective procercoid has a typical tegument. The microvilli are shaped like a thorn compressed from the sides. They have an electron dense tip and a less dense base in which microfilaments are seen. Bodies, called disc-shaped and lamellated bodies, are described. The microvilli of the plerocercoid are characterized by a great variation in shape. The villi are bounded by two unit membranes. The lamellated bodies are especially well developed. The adult microvilli are uniform in shape. The lamellated bodies are few in young adults and disappear in mature worms.     

Morpho-functional specialization of the branching sporocyst of Prosorhynchoides borealis Bartoli, Gibson & Bray, 2006 (Digenea, Bucephalidae)

Sporocysts of Prosorhynchoides borealis were obtained from the marine bivalves Abra prismatica and studied using transmission electron microscopy. The sporocyst body consists of a mass of branching and intertwining hollow tubules that ramify through the host's digestive gland and gonads. This study investigated the ultrastructure of the sporocyst branches which comprise alternate distended areas (brood chambers) with a relatively thin body wall, narrower portions with a thicker body wall (constricted areas) and terminal regions. Pronounced differences between these areas were revealed in the structure of their tegument and body cavity lining, as well as in the cellular composition of the subtegumental layers. Body wall composition in distended areas was consistent with the specialization for cercarial nurture in the brood chambers. The structure of the constrictions suggested a dual role of nutrient absorption and physical separation of adjacent brood chambers. Two types of terminal region were identified, one specialized for the investigation and penetration of host tissues and the other, in which the germinal cells are formed, for cercarial production. The overall structure of the sporocyst branches helps explain why this linear modular system, i.e. brood chambers and constrictions continuously growing into the host tissue, enables the sporocyst's long-term existence and can continuously produce cercariae in numbers comparable with those produced by rediae and/or daughter sporocyst infrapopulations in other digeneans. The origin of the nuclei in the outer tegumental layer of some branching bucephalid sporocysts is also discussed.     

An ultrastructural study of alimentary tract development in the cercariae of Prosorhynchoides borealis (Digenea,Bucephalidae)

Podvyaznaya I. 2011. An ultrastructural study of alimentary tract development in the cercariae of Prosorhynchoides borealis (Digenea, Bucephalidae). —Acta Zoologica (Stockholm) 92 : 170–178. The development of digestive system in Prosorhynchoides borealis cercariae was studied using transmission electron microscopy. The foregut and caecum primordia arise in early cercarial embryos as two adjoining cellular cords. The primordial pharynx appears as a cluster of myoblasts in the mid‐part of the foregut primordium whose proximal end abuts onto the ventral embryonic tegument. Later, a lumen develops within the gut primordia and their component cells form the embryonic cellular epithelium with an essentially similar structure in the foregut and caecal regions. Subsequently, the foregut epithelial cells merge to form a syncytium. This process proceeds asynchronously and the most proximal foregut area remains cellular for the longest time. The syncytial lining of the foregut establishes syncytial connections with secretory cytons differentiating in the surrounding parenchyma. These cytons produce secretory granules, which are transported through cytoplasmic connections to the foregut syncytium. Before cercariae reach maturity, their foregut epithelium becomes anucleate and continuous with the external tegument. By the end of cercarial development, numerous short lamellae appear on the luminal surface of the caecal epithelium. The caecal cells become involved in secretory activity as indicated by the presence of Golgi‐derived secretory bodies in their cytoplasm.     

Ultrastructure of cysts of E. coli

Ultrastructure of cysts of E. coli. International Journal for Parasitology4: 125–131. The cyst wall of E. coli in the mature stage comprises two distinct layers, and the cytoplasm contains many of the organelles observed in other amoebae.     

Convergence of the cyst in cysticercoids (Cestoda,Hymenolepidata) and the tegument in cystacanths (Acanthocephala)

It was shown that despite fundamental differences in the organization of the tegument of cystacanths and the cyst wall of cysticeroids, they have a number of features similar in localization, morphology, terms of formation, and functional value. These include a powerful outer layer of glycocalyx on the surface of the tegument, filling of the distal department with dense substance, and the presence of complicated fibrillar systems. It is supposed that the nature of these particularities is convergent and is determined by the similarity of the life cycles of Hymenolepidata and Acanthocephala.