Ultrastructure of genital system ducts of Diphyllobothrium latum (Cestoda:Pseudophyllidae): the ducts of the female reproductive system

The components of the female reproductive system of Diphyllobothrium latum, including ovary, ovicapt, oviduct, vitelline ducts, vitelline reservoir, vagina, seminal receptacle, ootype with unicellular Mehlis's gland, ootype-uterine duct and uterus were observed with the electron microscope. The epithelium of the female reproductive system ducts consists of a nucleate syncytial layer. Structural differences in apical surface of the ducts, the number of nuclei and organoids in syncytial layer as well as the number of underlaid muscles were revealed. The regional differentiations of the uterus wall were registered. The middle and distal region of uterus was covered with microtriches. The filamentous microtriches were observed in apical surface of vagina. The epithelium of seminal receptacle and distal region of uterus were underlaided by the powerful muscle layers. The fertilization canal was revealed. It was shown that the formation of egg shells implemented by the deposit of vitelline globules in their surface in the ootype-uterine duct. Structural and functional differences of different parts of female apparatus in various groups of cestodes are conditioned by species biology.     

Scanning and transmission electron microscopy of the female reproductive system of Schistosoma margrebowiei Le Roux, 1933

Transmission electron microscopy shows that the uterus of female Schistosoma margrebowiei possesses the same ultrastructure as that of the tegument but lacks spines and sense organs. It does not possess secretory cells and opens at the gonopore which by scanning electron microscopy was seen to be composed of numerous leaf-like protrusions. The morphology of the ovary is comparable with that of other Digenea. Immature and mature ova possess cortically arranged granules and occur within the posterior zone of the ovary. Cilia and lamellae line the luminal surface of the oviduct and ootype, the lamellae running unidirectionally along the duct. Only a single type of secretory cell is seen within Mehlis' gland and this produces dense bodies which are associated with Goldi bodies. Narrow cytoplasmic channels supported by microtubules deliver these secretory bodies to the ootype. The vitelline duct is lined with cilia and lamellae and the vitelline gland contains four types of cells, S1, S2, S3 and S4. Calcareous corpuscles are found within mature S4 cells.     

Immunocytochemical demonstration of neuropeptides in the fish-gill parasite, Diclidophora merlangi (Monogenoidea)

Using the indirect immunofluorescence technique, immunoreactivity (IR) to three mammalian and one invertebrate regulatory peptide has been demonstrated in the nervous system of the monogenean gill parasite Diclidophora merlangi. IR to pancreatic polypeptide (PP), peptide tyrosine tyrosine (PYY) and FMRFamide was evident throughout central and peripheral nervous tissues, whereas vasoactive intestinal polypeptide (VIP)-IR was confined to a portion of the longitudinal ventral nerve cords. Staining patterns revealed the orthogonal arrangement of the nervous system consisting of paired cerebral ganglia, connecting post-pharyngeal commissure, three pairs of longitudinal nerve cords and associated neurones. PP-IR, PYY-IR and FMRFamide-IR were intense throughout the central nervous system of the worm. A small plexus of nerve fibres and somata in each peduncle was immunoreactive for FMRFamide and provided innervation to each of the eight posterior clamps. In the peripheral nervous system, PP-IR, PYY-IR and FMRFamide-IR occurred in an extensive nerve-net with fine, possibly sensory nerve endings in the tegument. PP-IR was also present in nerve fibres in the walls of the ootype, seminal vesicle and uterus. PYY- and FMRFamide-IRs, while evident in nerve fibres of the ootype wall, were also present in a distinct population of cells that encircles the ootype, and which are linked to it by fine cytoplasmic connectives. The majority of these somata were bipolar or multipolar. PYY-IR and FMRFamide-IR were also associated with nerve fibres and bipolar cells in the wall of the vitelline reservoir. Regulatory peptides would appear to play an integral role in neuronal functioning and egg development in D. merlangi.     

In vitro studies on the functional maturation and locomotion of sperm in a free-living nematode, Panagrellus redivivus

In the seminal vesicle of male Panagrellus redivivus the sperm are normally rounded, non-motile and have cytoplasmic organelles randomly scattered throughout the whole cell body. Sperm become amoeboid in the uterus of the female with a clear anterior region capable of producing pseudopodia and an arch-shaped rigid posterior region containing numerous organelles. The sperm arrange themselves in the form of a chain in the uterus attaching themselves anterio-posteriorly, however sperm entering the post-vulvar uterine sac do not form a chain and remain scattered. Approximately eight hours after insemination the sperm in the uterus stop producing pseudopodia. Pseudopodial formation recommences in the seven to eight anteriormost sperm in the chain as they reach seminal receptacle.     

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.     

Morphology and function of the female reproductive system of Ebalia tumefacta (Decapoda,Brachyura, Leucosiidae)

In this article, the morphology and function of the female reproductive organs of Ebalia tumefacta were investigated using histological methods. While the vagina conforms to the concave type, the study reveals a new orientation of seminal receptacle compartments. The seminal receptacle consists of two chambers, which are oriented in anterior‐posterior direction. This is in contrast to the dorso‐ventral orientation of seminal receptacle chambers in all other known brachyuran crabs. The anterior chamber is lined by cuticle, whereas the posterior chamber is covered with a holocrine glandular epithelium. The oviduct connection is located ventrally, close to the opening of the vagina. The oviduct orifice is characterized by a transition of the epithelium lining of the oviduct to the seminal receptacle holocrine glandular epithelium. Special features are muscle fibers, which are attached to the oviduct orifice and to the sternal cuticle as well. The muscle fibers can be found exactly at that point where the oviduct opens into the seminal receptacle and are secondly attached to the sternum beneath. This musculature is newly described for Eubrachyuran crabs. This musculature can be interpreted as an important feature in the fertilization and egg‐laying process in relation to supporting and controling the inflow of eggs into the seminal receptacle lumen. These new discoveries were compared to the known pattern of an Eubrachyuran seminal receptacle. J. Morphol. 276:517–525, 2015. © 2014 Wiley Periodicals, Inc.     

Ultrastructure and cytochemistry of the tegument of Atriaster heterodus (Platyhelminthes: Monogenea)

The tegument of the polyopisthocotylean monogenean Atriaster heterodus Lebedev & Parukhin, 1969 was studied using transmission electron microscopy. The outer syncytial layer of the tegument is connected to the internal cell bodies by cytoplasmic extensions which interweave between the muscular fibres. The free surface of the syncytium has projections of the external membrane which are similar to microvilli. The undulating basal membrane, with numerous narrow elongate projections, is associated with the basal lamina situated between the syncytial and muscular layers. The cell bodies and syncytial layer of the tegument exhibit two types of vesicles, one with fibrous contents and one with electron-dense contents; these were analysed using two cytochemical tests, the E-PTA and alcian blue methods, used for the first time on monogeneans.     

Developing embryo and cyclic changes in the uterus of Peripatus (Macroperipatus) acacioi (Onychophora,Peripatidae)

Female reproductive tracts of the viviparous neo-tropical onychophoran Peripatus acacioi have been examined at different times throughout the year, and the altering relationship between the developing embryo and the uterus is described. Depending on her age and time of year, the female may have one or two generations of embryos within her uterus. The uterine wall consists of a thin outer epithelium and basal lamina, three layers of muscles, and a thick basal lamina beneath an inner epithelium lining the uterus lumen. These layers are consistent along the length of the uterus apart from the inner epithelial lining, which varies according to position in the uterus and the developmental stage of embryos contained in the uterus. Early embryos are positioned along the length of the uterus and therefore have space in which to grow. During cleavage and segment formation, each embryo is contained within a fluid-filled embryo cavity that increases in size as the embryo grows. Morulae and blastulae are separated by lengths of empty uterus in which the epithelial lining appears vacuolated. Until the process of segment formation is complete, the embryos are attached to a placenta by a stalk and remain in the same part of the upper region of the uterus. As these embryos grow, the lengths of vacuolated cell-lined uterus between them decrease. Each embryo cavity is surrounded by the epithelial sac, the maternal uterine epithelium, which becomes overlaid by a thin layer of cells, the embryo sac, which is believed to be of embryonic origin. The placenta is a syncytial modification of the epithelial sac located at the ovarian end of each embryo cavity covered by the embryo sac and is analogous to the mammalian noninvasive epitheliochorial placenta. Segment-forming embryos have their heads directed toward the ovary. As the embryo gets longer during segment formation, its posture changes from coiled to flexed. Once segment formation is complete, the embryo loses contact with its stalk, an embryonic cuticle forms, and the embryo turns around so that its head is directed toward the vagina. The embryo escapes from its embryo sac and moves to the lower part of the uterus. In the lower part of the uterus, the straightened fetuses are first unpigmented but subsequently become pigmented as the secondary papillae on the body surface form and an adult-type cuticle forms beneath the embryonic cuticle. While the embryos are contained within their embryo cavities, nutrients are supplied by the placenta. Throughout development the mouth is open and in the mature fetus the gut is lined by peritrophic membrane and material is present in the gut lumen. Trachea have been observed only in fetuses that were ready for birth. Insemination, cyclical changes in the uterine epithelium, and the nature of the cuticle shed at parturition are discussed. © 1995 Wiley-Liss, Inc.     

Cyton II: A subtegumental cell type in the cercaria of Schistosoma mansoni

In Schistosoma mansoni cercaria, an aggregate of subtegumental cells is found in a small, dorsoanterior area of the body (middivision). These cells are nestled between two laterally positioned flame cells and the muscle that delimits the anterior end of the body, and the anterior end of the central ganglion. This highly amorphous cell type, designated as cyton II, has a heterochromatic nucleus and a cytoplasm that is elaborated into coarse, tortuous processes. Its cytoplasm contains ribosomes, mitochondria, sparse amounts of endoplasmic reticulum, and two types of circular-to-oval concentric membranous bodies. One type has an electron-dense core and measures 200–250 nm on the short axis, and the other is completely membranous and measures 100–125 nm on the short axis. The cell body of cyton II communicates with the tegument that covers a small, dorsoposterior area of the anterior organ (oral sucker); however, we could not confirm a tegumental connection with the body division. When cercariae transform into schistosomules, the concentric membranous bodies of cyton II migrate into the anterior organ's tegument via cytoplasmic processes of the cell. The major function of previously described cells that have similar membranous bodies is to supply additional membranes to the outer tegument during development into an adult worm. A multilaminated outer membrane is an adaptation to the survival of the schistosomule and adult worm in the bloodstream of the vertebrate host (Hockley amd McLaren [′73]). The presence of membranous bodies from cyton II in the tegument does not confirm that this cell type participates in the formation of multilaminated membranes. Its precise function remains to be determined. © 1995 Wiley-Liss, Inc.     

Gyrodactylid developmental biology: historical review, current status and future trends

In the viviparous gyrodactylids, embryos develop one inside another within the parental uterus, a phenomenon with major implications for the biology of this species-rich group. Development occurs via two routes: first-born daughters develop at the centre of an embryo cluster in utero, whereas all other daughters develop from oocytes. The resulting offspring are, however, morphologically indistinguishable. We review here the history of gyrodactylid embryology in the context of current knowledge and, present additional cytogenetic and ultrastructural observations of embryonic development. These progenetic parasites are highly modified for viviparity; oocyte maturation and sperm storage occur in a single chamber, the Egg Cell Forming Region, and a mature oocyte passes into the uterus after the birth of the preceding, fully developed offspring. The uterus has a syncytial lining derived from anterior and posterior cap cells. These cells are the first to differentiate in the female reproductive system and may be involved in controlling development. Embryos receive nutrients via the uterus rather than from vitelline cells. Traditionally, development of the first-born daughter has been considered a form of polyembryony, although paedogenesis has also been suggested. In contrast to previous studies, we could not trace lineage of the first-born daughter to a single quiescent macromere. However, only mitotic divisions have been conclusively observed in the intraembryonic generation, indicating an asexual origin. All other daughters are formed from meiotically derived oocytes by sexual reproduction or automictic parthenogenesis. The latter may involve pre-meiotic doubling of chromosomes, but the precise mechanism and the relative proportion of sexual and parthenogenetic offspring are unknown. Exceptionally, cleavage in Gyrodactylus spp. occurs by duets rather than quartets (a pattern previously only recorded in acoels) and is characterised by extensive cell rearrangements. Blastomeres may be connected by fine cytoplasmic processes or completely disassociated and are readily redistributed by the muscular actions of the parental uterus. This process resembles 'Blastomeren-Anarchie' of rhabdocoels but without the structural support of vitelline cells. It prevents generation of early cell fate maps and indicates regulative, rather than mosaic, development. Structures such as the gut and excretory system differentiate late, and are highlighted, together with the attachment apparatus, as examples of post-embryonic differentiation. Molecular and cellular techniques are now essential to further elucidate mechanisms of gyrodactylid reproduction, which will in turn contribute to current debates with animal embryology.     

Immunohistochemical localization of 36 and 29 kDa proteins in sparganum.

Antigenic proteins of 36 and 29 kDa were localized in Spirometra mansoni plerocercoid (sparganum) immunohistochemically by avidin biotin complex (ABC) staining. When polyclonal antibodies such as BALB/c mouse serum immunized with crude saline extract of sparganum or confirmed sparganosis sera were reacted as primary antibodies, the positive chromogen (3-amino, 9-ethylcarbazole) reactions were recognized at syncytial tegument, tegumental cells, muscle and parenchymal cells and lining cells of excretory canals. A monoclonal antibody (MAb) which was reacting to 36 and 29 kDa proteins in the extract of the worm was localized at the syncytial tegument and tegumental cells. The present results suggested that the potent antigenic proteins of 36 and 29 kDa in sparganum were produced at the tegumental cells and transported to the syncytial tegument.     

The study of the ultrastructure of the female reproductive system in a parasite of bats Allassogonoporus amphoraeformis (Digenea: Allassogonoporidae)

The morphology and fine structure of the female reproductive system of allassogonoporid trematode Allassogonoporus amphoraeformis have been described for the first time. The ovary consists of the germ cells being at various developmental stages and supporting cells of two types. The oviduct, seminal receptacle with its short duct and the proximal portion of Laurer's canal are lined by flattened cellular epithelium with lamellae and cilia on its luminal surface and well-developed basal infoldings. The distal part of Laurer's canal and metraterm are tegumental in structure and are characterized by sparse secretory inclusions and lacking of spines. Mehlis' glands of two types open into ootype. The uterus wall is composed of highly flattened epithelial cells surrounded by basal lamina and sparse muscle bundles. Vitelline lobules consist only of the vitelline cells at various developmental stages. The mature vitelline cells contain two types of inclusions: vitelline droplets and rarely scattered lipids. Vitelline ducts are lined by cellular epithelium with highly folded luminal surface and devoid of cilia. Presented results are compared with earlier obtained data on other lecithodendrioiden trematode Prosthodendrium ascidia ([symbol: see text], 1990).     

Development of the reproductive system of Echinostoma paraensei in Mesocricetus auratus analyzed by light and confocal scanning laser microscopy

This study was performed to gain insight into the maturation of the reproductive system of Echinostoma paraensei worms grown in an early infection of Mesocricetus auratus. Hamsters were infected with 100 metacercariae and necropsied on days 3, 5, 7, 10 and 14 post infection (dpi). Recovered flukes stained with hydrochloric carmine were preserved as whole mounts and analyzed by light and confocal scanning laser microscopy. The average worm recovery was 43.7 per host. Images of the male and female reproductive systems were taken. The ovary and anterior and posterior testis were evidenced on day 3, while the ootype and cirrus sac were present on day 5. Confocal imaging showed primordium testis and ovary as a cluster of primordial cells from day 3 onward. The testes, ovary, cirrus sac and uterus organs were already present during the first week of life. The two testes were seen as individual structures on 7 dpi while the cirrus sac and vitelline glands were in development. The ovary was connected to the uterus while the ootype was adjacent to it. Both testes were larger than the ovary, showing cells at different stages of development, but with few bundles of functional spermatozoa in 10 day-old worms. On day 14, eggs and spermatozoa were seen in the uterus and seminal vesicle, respectively, while oocytes appeared in the ootype as fertilized eggs. We conclude that the reproductive system of E. paraensei was functional on 14 dpi in the hamsters.     

An ultrastructural study of the early cercarial development in Prosorhynchoides borealis (Digenea: Bucephalidae) with special reference to formation of the primitive epithelium

Primitive epithelium and outer tegumental layer formation during early cercarial development was studied in Prosorhynchoides borealis using electron microscopy. It demonstrated that germinal cells freely floating in the sporocyst body cavity divide to give rise to naked cell aggregates. These early embryos are highly irregular in outline and are composed of blastomeres differing in size and structure. In embryos consisting of about 12-14 cells a few (possibly only two) superficial macromeres become concave and produce thin extensions which envelop the embryonic mass before fusing to form a syncytial primitive epithelium. This primitive epithelium forms syncytial connections with underlying embryonic cells. Primordial tegumental cells become apparent in late germinal balls below the primitive epithelium. These cells expand and fuse to give rise to an embryonic nucleated tegument. The embryonic tegument is connected to peripheral embryonic cells by thin cytoplasmic bridges until the basement lamina is formed. Subsequently, the primitive epithelium is shed by the embryos and the nuclei in the embryonic tegument undergo pyknotic degeneration. These results are analysed and compared with data from studies on other trematode species and it is concluded that the primitive epithelium is derived from the embryo in at least the majority of digeneans.     

Tegument and apical end organ fine structure in the metacestode and adult Proteocephalus ambloplitis

The tegument of plerocercoid and adult P. ambloplitis was examined. Differences in tegument structure existed between these two stages. Plerocercoids of P. ambloplitis lacked extensive vacuolization and unicellular gland cells characteristic of adult tegument. Plerocercoid microtriches were short and conoid; adult microtriches were lenticular with an extended, whip-like shaft. An inclusion, not previously reported from proteocephalid cestodes, is described. Adult tegument had ducts, originating from underlying unicellular glands, extending through the distal cytoplasm and opening to the exterior between microtriches.

The apical end organ cavity of P. ambloplitis contained numerous labyrinth-like spherical bodies. These structures appeared to be synthesized and secreted into the end organ by a thin cellular lining of the end organ. This lining was composed of discrete, filamentous cells believed to be modified subtegumental cell bodies. Spherical structures identical to those observed within the end organ cavity occurred within this cellular lining. The spherical bodies may be associated with enzymes necessary for tissue migration by the metacestode.     

Ultrastructural aspects of the oesophageal and reproductive systems of the equine parasite Strongylus vulgaris

The ultrastructure of the dorsal oesophageal gland ampulla and its relationship with the oesophagus, oesophageal ultrastructure, and control mechanisms in oesophageal activity were studied. Terminal ducts of the sub-ventral glands open through the oesophageal crown at the base of the buccal cavity. The terminal duct of the dorsal oesophageal gland running through the dorsal gutter opens to the exterior at the rim 'groove' of the buccal capsule. The posterior oesophageal region is clavate and the cuticle of the lumen folds to form outlet valves, 'valvulae'. An inconspicuous oesophago-intestinal valve (three lobes) connects oesophagus and intestine and is visualized in the open and shut position. In the female reproductive tract, with the exception of the uterus, the cells lie on a thick, irregular (convoluted) basal lamina. The apical plasma membrane of the uterus, and seminal receptacle, extend into the lumen by microvilli-like projections with which spermatozoa make intimate contact. The lumen of the uterus is filled with oocytes, fertilized and unfertilized. Testicular cells have two parts linked by a rachis. Spermatocytes are elongated with a large nucleus, distinct nuclear membrane, and many granules. The apical membrane of the rachis forms long microvilli-like projections with balloon-like tips. The amoeboid spermatozoa contain membrane specializations, a nucleus devoid of a membrane, and are enclosed by a pseudopodial-like extension.     

Wheat Streak Mosaic Virus-induced Cytoplasmic Expansion and Membrane Proliferation

The cytoplasmic volume of wheat streak mosaic virus-infected cells was significantly greater than that of cells in healthy control tissue. Ultrastructural examination revealed that mainly cellular membranes and ribosomes filled the expanded cytoplasm. Imperfectly spherical inclusions, containing continuous endoplasmic reticulum membranes at the periphery and a mixture of membranes and ribosomes in the centre, were observed near nuclei at early infection stages. The inclusions became larger as infection progressed. Membranes and ribosomes proliferated also throughout the cell, forming a matrix in which organelles and various cytopathic structures were enclosed. Numerous vesicles were observed in the cytoplasm of other WSMV-infected cells. Multi-layered membrane bodies were found at later infection stages. Virus particles were present in the central space of these myelin-like structures. The presence of apparently intermediate stages in myelin-like structure development in chloroplasts suggest that at least some of the myelin-like structures originated from the chloroplasts.     

Development and roles of vitelline cells in eggshell formation in Fasciola gigantica

Summary

In Fasciola gigantica, vitelline cells are the major contributors to the formation of the eggshell. The vitelline cells develop in vitelline follicles that are located in the posterior third of the adult parasite's body, in the areas lateral to the uterus and the testis. Mature vitelline cells are released and transported to the Mehlis' gland-ootype complex via a series of vitelline ducts. Based on ultrastructural features, the developing vitelline cells are classified into four stages: stem cell, protein-synthetic, carbohydrate-synthetic and mature cell stages. At the protein-synthetic stage, the eggshell globules are formed, whereas during the carbohydrate-synthetic stage glycogen particles and glycan vesicles are synthesized. The mature vitelline cells are detached from the nurse cells, and pass successively into the intrafollicular, interfollicular, longitudinal and transverse vitelline ducts, to be stored in the vitelline reservoir before being transported to the ootype via the median vitelline duct. At the same time, ova are transported from the ovary through the oviduct into the ootype lumen where each becomes surrounded by a number of vitelline cells. Vitelline cells secrete eggshell globules to surround a group of vitelline cells and an ovum in the ootype lumen, and these globules coalesce into the definitive eggshell. In the middle part of the uterus fertilization occurs, after which the eggshell is completely formed. Within the egg proper, vitelline cells break down, releasing glycogen and other products to nourish the developing embryo.     

Ultrastructure of the digestive tract of Gyliauchen nahaensis (Platyhelminthes, Digenea), an inhabitant of the hindgut of herbivorous fishes

Digenean parasites of vertebrates usually amplify the surface area of their gut by increasing the size of the absorptive caeca. Some members of the family Gyliauchenidae, however, have relatively small caeca but have a greatly expanded foregut. The morphology of the elongate gut of the digenean Gyliauchen nahaensis, an inhabitant of herbivorous fish of the family Siganidae, was examined by light and transmission electron microscopy. The extensive foregut, consisting of a mouth, pharynx, and esophagus, is lined with a syncytial tegument-like lining, which is connected to nucleated cell bodies sunken in the parenchyma. The apical cytoplasm in the mouth and anterior regions of the pharynx resembles that of the general body tegument, although some regional specialization is present. The lining of posterior regions of the pharynx is armed with large apical projections, which are thought to serve as filtration structures. The lining of the anterior and middle esophagus displays a peculiar form of surface amplification involving the formation of elongate flask-shaped invaginations of the apical cytoplasm. The cell bodies associated with these regions are rich in secretory vesicles and it is proposed that these regions of the esophagus are expanded to promote extracellular digestion. The posterior region of the esophagus lacks the invaginations of other esophageal regions, but displays instead large surface projections. The caeca consists of columnar cells lined by extensive apical microlamellae. The peculiar gut morphology of G. nahaensis, coupled with alterations in the arrangement of suckers, is interpreted to be an adaptation to the predominantly herbivorous diets of the definitive hosts.     

Observations on the attachment by the monogenean, Anoplodiscus australis, to the caudal fin of Acanthopagrus australis

The unarmed haptor of Anoplodiscus australis erodes the epidermis and attaches to the basal lamina above the stratum compactum in the caudal fin of Acanthopagrus australis by an eosinophilic, weakly PAS-positive and strongly toluidine blue-positive secretion. Ultrastructural evidence shows that the adhesive secretion, in the form of rod-shaped bodies, is produced by subtegumentary cells that connect by ducts to the thin, ventral syncytial tegument of the haptor; these bodies pass into the tegument, then coalesce in the host-parasite interface. This means of attachment has developed by an enhancement and regional specialization of the subtegumentary secretory cells associated with a syncytial tegument in monogeneans and some other platyhelminths. The available evidence indicates that the adult parasite is permanently attached.