Ultrastructural and histochemical observations on the epidermis, presumptive tegument and glands of the miracidium of Gigantocotyle explanatum (Trematoda:Paramphistomidae)

Dunn T. S., Hanna R. E. B. and Nizami W. A. 1987. Ultrastructural and histochemical observations on the epidermis, presumptive tegument and glands of the miracidium of Gigantocotyle explanatum (Trematoda: Paramphistomidae). International Journal for Parasitology17: 885–895. The miracidium is invested with 20 ciliated epidermal cells arranged in four tiers (6: 8: 4: 2 = 20). Non-ciliated ridges of cytoplasm, located between the epidermal cells, are continuous with an extensive multivesiculate syncytium which underlies the body musculature and comprises the main bulk of the miracidium. It is suggested that the syncytium represents the presumptive sporocyst tegument. Two distinct types of glands are present in the anterior region of the miracidium, viz. a large, syncytial apical gland and a single pair of small, unicellular lateral glands. The apical papilla is formed by the bounding membrane of the apical gland, which is elevated into a complex network of anastomosing lamellae. The lateral glands terminate in discrete rosetteshaped areas on the apical papilla. The possible function of glands in digenetic miracidia and the nature of their secretions are discussed.     

Stereoscan studies of eggs, free-swimming and penetrating miracidia and early sporocysts of Fasciola hepatica.

The egg of Fasciola hepatica has a smooth surface with a slightly elevated circle marking the fracture of the operculum. The operculum and the aperture have crenated edges. The epithelial cells of the miracidium are covered with long cilia. When miracidia are vibrated in an ultrasonic cleaner the cilia of the epithelial cells of the four posteroir tiers are broken off only leaving longitudinal rows of cilium stubs, whereas the cilia of the first tier are still retained. The apical papilla is provided with a dorso-ventral furrow, multiciliated pits and isolated sensory cilia. The narrow intercellular ridge is smooth, whereas the epithelial cells have small cytoplasmic knobs between the cilia. The penetration into the snail (Lymnaea truncatula) and the transforamtion into sporocyst may be separated into three phases. (1) Less than 1 min after attachment to the snail the ciliated cells of the anterior tier are shed and swim away. (2) The cilia of the remaining cells beat violently and after about 5 min most cilia are broken off near the cell surface. The miracidium remains for about 15 min embedded as far as the intracellular ridge receptors (lateral papillae and sheathed ciliated nerve endings). During this period extensive contraction and relaxation of the body are performed. (3) The final penetration of the snail epithelium takes about 15 min. Simultaneously with the penetration into the snail tissue the "bald" cells (epithelial cells with cilium stubs only) of the four posterior tiers loosen, florm globules and fall off. The surface below the cells is smooth and in cytoplasmic continuity with the intercellular ridge and the apical papilla, and this syncytium forms the later tegument of the sporocyst. After a few days the tegument of the sporocyst is provided with microvillus-like projections and the apical papilla and sensory structures are lost.     

Scanning electron microscope observations on the miracidium of Schistosoma

Miracidia of two species of Schistosoma, viz. haematobium and japonicum, were studied with the scanning electron microscope to more clearly visualize what is seen with the light microscope and the transmission electron microscope, and more specifically, to relate the structure of the apical papilla to its function in snail penetration.The apical papilla of schistosome miracidia is composed of corrugated areas which form tiny suckerlike cups, presumably used by the miracidium to facilitate attachment to the snail during penetration. A lateral opening (secretory pore) on the apical papilla and short stubby apical cilia (tactile or sensory) are also demonstrated.     

Schistosoma mansoni: penetration apparatus and epidermis of the miracidium

Free swimming miracidia of Schistosoma mansoni were studied with the electron microscope for the purpose of describing the penetration apparatus and the epidermis. The penetration apparatus was composed of 3 unicellular glands which contain membrane-bound vesicles containing macromolecular diglycols. Each gland contained a nucleus, rough endoplasmic reticulum, Golgi complexes, numerous mitochondria, and glycogen stores. Each gland cell opened to the exterior through the apical papilla.The surface of the miracidium, with the exception of the apical papilla, was covered with ciliated epidermal cells containing numerous mitochondria, membranous bodies, and glycogen. No nuclei were detected within these epidermal cells. Intercellular ridges connecting with subepidermal cytons interrupted the epidermal cells at numerous points. The ridges were joined to the epidermal cells by septate desmosomes. Beneath the epidermal cells were found circular and longitudinal muscle bundles.Sensory structures of various types were associated with the outer covering. These consisted of (1) numerous “knob-like” cytoplasmic projections associated with epidermal cells, (2) bulbous, lamelloid structures with external cytoplasmic projections, and (3) ciliated nerve endings with posterior epidermal tiers and ciliated nerve pits associated with apical papilla.     

Description of embryonic development and ultrastructure in miracidia of Cardiocephaloides longicollis (Digenea,Strigeidae) in relation to active host finding strategy in a marine environment

The functional ultrastructure and embryonic development of miracidia in naturally released eggs of the trematode Cardiocephaloides longicollis were studied using light and transmission electron microscopy. This species has operculated eggs and embryogenesis occurs in the marine environment before an actively infecting ciliated miracidium hatches. Six different developmental stages were identified. The lack of pores in the eggshell indicates its impermeability and the miracidium's dependency on glycogen nutritive reserves, contained in numerous vitellocytes in early embryos. As the development advances, these merge into larger vitelline vacuoles that encircle the miracidium and may aid its hatching. Tissue and primary organ differentiation were observed in advanced stages, i.e., terebratorium, glands, cerebral ganglion, peripheral sensory endings, and eyespots. The anterior part of the body contains a single apical and paired lateral glands, as well as two types of sensory endings, which permit location, adhesion, and penetration of the host. No previous studies describe the embryonic development and ultrastructure of miracidia in strigeids, however, some of the structural features shared with other, well described species with unknown life cycles are emphasised. This study highlights that ultrastructural data have to be interpreted in relation to parasite biology to understand the structural requirements of specific parasite strategies.     

Development of Trichobilharzia australis Blair & Islam, 1983 in the snail, Lymnaea lessoni Deshayes and in an experimental definitive host, the Muscovy duck

The development of Trichobilharzia australis Blair & Islam, 1983 in the intermediate host, Lymnaea lessoni Deshayes and in experimental definitive hosts, Muscovy ducks is described. 24 hours after entry into the snail, miracidia had lost their cilia, epidermal plates and lateral processes and became young mother sporocysts. They were located in the tissues of the head-foot organ of the snail and were oval in cross section but still retained the shape of a miracidium, and measured 0.058-0.066 X 0.041-0.049 mm. From the seventh day onward young mother sporocysts were tubular, thin-walled, irregular in shape and were in the tissues of the lung and kidney of the snail. On the 24th day mature mother sporocysts and young daughter sporocysts were found in the digestive gland. Between the 24th and 29th day mature daughter sporocysts with fully developed cercariae ready to emerge, or already emerged, could be seen in the digestive gland of the snail. Cercariae emerged from the snail from the 29th to 46th day after exposure at 25 degrees +/- 1 degree C. The prepatent period of T. australis in the Muscovy ducks was 22 to 42 days after the beginning of exposure to cercariae.     

Morphology of the nasal fossae and associated structures of the hamster (Mesocricetus auratus)

The hamster nasal cavity consists of vestibular, non-olfactory and olfactory portions. Much of the non-olfactory nasal cavity surface is lined by cuboidal, stratified cuboidal, and low columnar epithelia, devoid of cilia. Goblet cells and ciliated respiratory epithelium are present over only a small portion of the nasal cavity surface. The largest glandular masses in the hamster nose are the maxillary recess glands, the vomeronasal glands and the lateral nasal gland 1; these three glands contain neutral mucopolysaccharides (PAS-positive). Other nasal glands contain both acidic and neutral mucopolysaccharides; the staining reaction for acidic mucopolysaccharide is stronger in goblet cells and olfactory glands than in the other nasal glands. The ducts which open into the nasal vestibule are the excretory ducts of compound tubuloacinar serous glands. The one major PAS-positive gland whose duct opens into the nasal vestibule is the lateral nasal gland 1. The ducts of the compound tubuloacinar vomeronasal glands open into the lumen of the vomeronasal organ, which is connected to the ventral nasal meatus by means of the vomeronasal duct. The ducts of the branched tubuloacinar maxillary recess glands open into the maxillary recess. Few ducts open into the caudal half of the nasal cavity.     

Lecithochirium furcolabiatum (Jones 1933), Dawes 1947: the miracidium and mother sporocyst.

Experimental infections of the marine topshell Gibbula umbilicalis with Lecithochirium furcolabiatum (Digenea: Hemiuroidea) have allowed the development of a model system which will enable further studies of the molluscan host response. The long-lived intertidal prosobranch host is easily maintained in the laboratory, and experimental infection rates of 98% were consistently achieved. The miracidium and mother sporocyst have been studied at both light and ultrastructural levels, providing the first account of the morphology of these stages in Hemiuridae. The ingested egg hatches within the host intestine, treatment with L-cysteine and alkaline pH stimulating miracidial emergence in vitro. The general body surface of the miracidium is devoid of spines or cilia, the latter being restricted to four plates near the anterior extremity. The miracidium swims actively prior to penetration of the gut wall, the sporocyst being released from the miracidial epidermal coat within the haemocoel. Within 5 weeks of infection, the filamentous mother sporocyst contains 1 to 3 oval germ balls, daughter sporocysts being recorded free within the digestive gland haemocoel 7 weeks later. Twenty three weeks after ingestion of eggs, the daughter sporocyst extends into the host gill filaments, containing cystophorous cercariae ready for emergence.     

Proteomic Analysis of the Schistosoma mansoni Miracidium

Despite extensive control efforts, schistosomiasis continues to be a major public health problem in developing nations in the tropics and sub-tropics. The miracidium, along with the cercaria, both of which are water-borne and free-living, are the only two stages in the life-cycle of Schistosoma mansoni which are involved in host invasion. Miracidia penetrate intermediate host snails and develop into sporocysts, which lead to cercariae that can infect humans. Infection of the snail host by the miracidium represents an ideal point at which to interrupt the parasite’s life-cycle. This research focuses on an analysis of the miracidium proteome, including those proteins that are secreted. We have identified a repertoire of proteins in the S. mansoni miracidium at 2 hours post-hatch, including proteases, venom allergen-like proteins, receptors and HSP70, which might play roles in snail-parasite interplay. Proteins involved in energy production and conservation were prevalent, as were proteins predicted to be associated with defence. This study also provides a strong foundation for further understanding the roles that neurohormones play in host-seeking by schistosomes, with the potential for development of novel anthelmintics that interfere with its various life-cycle stages.     

腔阔盘吸虫尾蚴及后蚴穿刺腺等腺体的组织化学及其功能的初步研究

本文报道应用组织化学反应方法初步观察了腔阔盘吸虫(Eurytrema coelomaticum)尾蚴及后蚴体中单细胞腺的组织化学成分及其生理功能。尾蚴的5对大单细胞腺主要分泌粘蛋白、酸性粘多糖及微量碱性蛋白质,当子胞蚴被排到外界时,此腺体物质分泌出充满子胞蚴内囊腔并包被着各尾蚴。尾蚴在此腺体分泌物保护下渡过其在外界生存的时间。尾蚴的4对小单细胞腺主要包含中性糖蛋白及结合氨基的蛋白质(可能是含酶物质),此腺体物质可能是在尾蚴进入昆虫宿主(草螽)体内穿钻其胃壁进入血腔时分泌出能溶解胃壁组织帮助尾蚴的穿钻行为。成熟后蚴的穿刺腺对PAS反应呈强阳性,其分泌物可以溶解囊蚴的囊壁,使后蚴迅速脱囊。各幼虫期其他器官组织的组化成分也经观察。     

Functional morphology of the mammiliform penial glands ofLittorina saxatilis (Gastropoda)

Summary The functional morphology of the mammiliform penial glands ofLittorina saxatilis has been investigated with both light and electron microscopy. These penial glands line the ventral edge of the penis and orient with the female mantle during copulation. Secretions are released from the penial glands to this interface where they probably function in adhesion. The penial gland secretions comprise heterogeneous granules as well as apocrine and mucous secretions. The heterogeneous granules are produced in separate multicellular glands arranged in a series of lobes that lie outside a thick smooth muscle layer enclosing the lumen. Each glandular lobe is surrounded by a thin layer of smooth muscle. Secretions are transported in individual cellular processes that pass through the thick smooth muscle layer and empty into the lumen. Surrounding the lumen is an epithelium containing apocrine secretory cells as well as occasional goblet-type, mucous cells. The combined action of the muscles forces secretions out of the lumen through the penial papilla, onto the external surface of the mammiliform penial gland. Longitudinal muscles extend into the penial papilla enabling its protrusion or retraction. Retraction of the penial papilla following secretion release is thought to create negative pressure beneath the penial gland producing suction adhesion. The visco-elastic properties of the penial gland secretion are qualitatively different from foot mucus and may represent specialization to an adhesive function.     

Histological study of the development of Fasciola hepatics in Lymnaea truncatula, L. glabra and L. palustris infested at hatching]

The development of Fasciola hepatica is histologically analysed in Limnaea truncatula, L. glabra and L. palustris infested at hatching with a single miracidium. The development of the redial generations of Fasciola is not affected by the species of snail host but depends on growth of the snail. In snails of size within 2 mm (considered at the day 49 of infestation to 20 degrees C), the rediae show a delay of maturity compared with rediae observed in snails of higher sizes. The distribution of redia 1 of generation 1 should have an influence on growth of the snail host.     

Immunocytochemical studies on the localization of pancreatic-type phospholipase A2 in rat stomach and pancreas, with special reference to the stomach cells

Using a specific polyclonal antibody raised against rat pancreatic phospholipase A2 (PLA2), we investigated the localization of the enzyme in the rat pancreas and stomach by light and electron microscopy. In the pancreas, the enzyme was localized in the acinar cells, whereas the pancreatic islets showed no immunoreaction. In the stomach, the PLA2 reactive with the anti-pancreatic PLA2 antibody was distributed exclusively in the gastric glands, but not in the gastric pits or the pyloric glands. On the section of the stomach subjected to immuno- and PAS-staining, immunopositive cells were not the PAS-positive cells located in the gastric pit and the neck region of the gastric gland. Immunopositive cells were present from the neck to the bottom of the gastric gland. Immunoelectron microscopic observation revealed that the immunogold-labeled cell had a highly-developed rough endoplasmic reticulum in the basal cytoplasm and characteristic zymogen granules in the apical cytoplasm. Taking into account the cell position in the gastric gland, the immunopositive cell could therefore be identified as a chief cell. Since no double stainability with PLA2 and PAS was observed in the same cell, it is suggested that PLA2 could be used cytochemically as a marker enzyme of the chief cell in the gastric gland at the light-microscopic level. From the immunoelectron microscopic findings, we believe that the PLA2 in the stomach is released into the lumen of the stomach by exocytosis and could function as a digestive enzyme in the alimentary tract, like the PLA2 secreted from the pancreas. Other possible roles of the PLA2 in the stomach are discussed.     

Gland cells associated with the alimentary tract of a monogenean, Diclidophora merlangi

Three distinct groups of unicellular glands open into the buccal cavity, prepharynx, and oesophagus, respectively, of Diclidophora merlangi. Buccal glands produce a dense, acidophilic secretion of protein-rich droplets that are discharged from duct-like extensions of the glands by eccrine secretion. Prepharyngeal glands are extensive and contain basiphilic secretory droplets of varying density and characterized by the presence of one or two dense core-like inclusions. The droplets are PAS-positive and reactive for protein, and accumulate in the gland cell apices which form part of the lining to the prepharynx lumen. They are released in large numbers by apocrine secretion or, individually, by an eccrine secretory mechanism. Oesophageal glands are acidophilic and contain electronlucid, PAS-positive droplets that develop a crystalline appearance prior to release via either eccrine or apocrine secretion. Differences in ultrastructure and histochemistry indicate the glands are also functionally separate, and their probable role in feeding and extracellular digestion of blood in the worm is discussed.     

The morphology and life-cycle of Trichobilharzia parocellata (Johnston & Simpson, 1939) Islam & Copeman, 1980 from the visceral blood vessels of Australian anatids

Summary The morphology of Trichobilharzia parocellata from the portal and mesenteric blood vessels of Anas gibberifrons and A. superciliosa from northern Australia is described. The life-cycle was completed in domestic Muscovy ducks exposed to Cercaria parocellata from naturally infected Lymnaea lessoni. Adults of T. parocellata are distinguished from closely related species by the point of caecal reunion in the male, the number of testes, the nature of the tegument and the species of snail hosts. The miracidia differed from all others in the genus except T. indica in having a pair of coarsely granular posterior secretory glands, a pair of apical glands, a papilla on each side in front of the lateral processes and 18 to 20 germinal cells in a single germinal mass. The prepatent period of T. parocellata in Muscovy ducks was only 11 days after exposure. Pigeons did not become infected. ac]19840624     

Fine structure of the spermatheca and of the accessory glands in Orchesella villosa (Collembola, Hexapoda)

The spermatheca and the accessory glands of the collembolan Orchesella villosa are described for the first time. Both organs exhibit ultrastructural differences, according to the time of the intermolt in which the specimens were observed. A thick cuticular layer lines the epithelial cells of the accessory glands. In the reproductive phase, they are involved in secretory activity; a moderately dense secretion found in the apical cell region opens into the gland lumen. Cells with an extracellular cistern are intermingled with the secretory cells. These cells could be involved in fluid secretion, with the secretory product opening into the cistern which is filled with an electron-transparent material. After the reproductive phase, the gland lumen becomes filled with a dense secretion. The accessory gland secretion may play a protective role towards the eggs. The spermatheca is located between the accessory glands; its epithelium is lined by a thin cuticle forming spine-like projections into the lumen and consists of cells provided with an extracellular cistern. Secretory cells, similar to those seen in the accessory glands, are missing. Cells with a cistern could be involved in the production of a fluid secretion determining sperm unrolling and sperm motility.     

Sensory receptors of the miracidium of Gigantocotyle explanatum (Trematoda:Paramphistomidae)

Five types of sensory receptors are described. Both uniciliated and multiciliated nerve endings occur on the apical papilla. The former structures possibly have a tango- or rheo-receptive function, while the latter may have a chemoreceptive function. A number of uniciliated sensory structures are also present embedded within the intercellular ridges. A pair of unciliated lateral papillae are located in the intercellular ridge separating the first and second tiers of epidermal cells. Each is associated with a number of sheathed unciliate nerve bulbs. A pair of internal “lamellate ciliary organs” are ascribed a photoreceptive function. Each comprises a cylindrical cell body enclosing a large cavity, into which project eight or more cilia bearing a number of concentrically arranged spherical lamellae. A single unicellular “conical organ”, covered with microvilli, projects into an extracellular space, bounded in part by the lateral glands. This structure may represent a second type of photoreceptor, or alternatively may serve as a gyroscopic device.     

The rôle of the calyx and poison gland of Cardiochiles nigriceps in the host-parasitoid relationship

Parasitism of Heliothis virescens by Cardiochiles nigriceps reduced the growth of the host. Both the poison gland and the calyx of the female parasitoid were important in reducing the growth of the parasitized host. Injections of poison gland contents (0·04 gl/larva) or calyx fluid (0·04 gl/larva) into H. virescens larvae did not affect their growth. However, a mixture of the two glands (1:1) at this low dosage significantly reduced the weight gained by Heliothis larvae.     

Comparative morphology,functions, and homologies of the coxal glands in oribatid mites (Arachnida: Acari)

1. Forty-eight species of oribatids in 37 families representing most of the superfamilies were collected from various environments (littoral, salt marsh, litter, sod, and freshwater) and sectioned. 2. The coxal gland is composed of a sacculus and a labyrinth in all stages of all oribatid species. Muscles, originating on the body wall, insert at several points on the thin-walled sacculus which opens into the labyrinth. The labyrinth has an internal, chitinous supporting skeleton. The type A labyrinth has 3–180° bends, producing four parallel regions, and occurs in all inferior oribatids. The type B labyrinth has 1–180° bend, producing two parallel regions, and occurs in all superior oribatids. The coxal gland duct and the lateral gland duct join, penetrate the body wall, and empty into the posterior end of the podocephalic canal. All oribatids have lateral accessory glands, but only inferior oribatids have rostral and medial glands. Three ductless coxendral bodies are always present. 3. The labyrinth length in oribatids is correlated with body size and the environment of the species. Oribatids from sod, leaflitter, or moss show a simple correlation of labyrinth length (X) to total body length (Y) where Y = 4.64X. Freshwater species have a labyrinth length greater than that of comparably sized terrestrial species and salt water (littoral) species have a labyrinth length less than that of comparably sized terrestrial species. There is a greater reduction in labyrinth length in species restricted to salt marshes than in species not restricted to salt marshes. 4. The probable function of oribatid coxal glands is osmoregulation. Hemolymph filtration would occur across the sacculus by positive hemolymph pressure and contraction of the sacculus muscles. Resorption of ions would occur in the labyrinth, which is noncollapsible due to the internal skeleton. The hypothesis is that in freshwater species the rate of filtration is high and resorption of ions would have to be very efficient, therefore they have an elongated labyrinth; but in salt water species water loss must be minimized and preservation of ions would be a disadvantage, therefore they have a shortened labyrinth. Excre ion may also be a function of the coxal glands. The lateral gland may possibly function as an endocrine gland involved with production of a molting hormone. The rostral glands in inferior oribatids may have a salivary function. 5. The coxal glands of Peripatus, some millipedes, apterygote insects, decapod crustaceans, and all arachnid orders are homologous. The Tetrastigmata, Notostigmata, Cryptostigmata, and soft ticks have typical arachnid coxal glands. The coxal glands of higher Prostigmata may be modified into salivary, silk, or venom glands. The coxal glands in Mesostigmata, Astigmata, and hard ticks are lacking or highly modified.