Oogenesis in the free proglottis ofTrilocularia acanthiaevulgaris (Cestoda,Tetraphyllidea)

The early (ovarian) stages of oogenesis inTrilocularia acanthiaevulgaris have been studied by light microscope histochemistry and transmission electron microscopy. The process proceeds as far as meiotic prophase in the primary oocyte. The oogonia and early immature primary oocytes occupy the anterior and outer edges of the ovary and are typically undifferentiated cells, showing a high nucleo-cytoplasmic ratio. The scant cytoplasm is packed with free ribosomes and contains a small number of mitochondria and a few short strands of granular endoplasmic reticulum (GER). The oogonia undergo a number of mitotic divisions, marked by the presence of centrioles. The immature primary oocytes enter meiotic prophase, as evidenced by the appearance of nuclear synaptonemal complexes. The maturing primary oocytes, which occupy the inner, central region of the ovary, undergo a growth phase that is accompanied by an increased nucleolar volume and export of RNA to the cytoplasm via nuclear pores, and by an increase in the number of mitochondria. A GER network develops and, together with the Golgi complexes, is involved in the production of a small number of cortical granules. The GER often takes the form of concentric cisternae. Numerous lipid droplets are also present in the cytoplasm. The mature primary oocytes predominate in the posterior region of the ovary, near the oviduct. They represent a resting phase in development, in which cellular activity is minimal. Lipid droplets are abundant and the cortical granules remain in more central regions of the cell and do not migrate to the periphery of the cell. The ovary contains a second, non-germinal type of cell, the follicle cell. The cell body is smaller in size than the oogonia, and cytoplasmic processes from it ramify around the periphery of the ovary. The different cell types within the ovary are embedded in a cytoplasmic matrix that contains a number of organelles.     

Spermatogenesis and the fine structure of the mature spermatozoon in the free proglottis ofTrilocularia acanthiaevulgaris (Cestoda,Tetraphyllidea)

Spermatogenesis and the structure of the mature spermatozoon ofTrilocularia acanthiaevulgaris have been studied by light microscopic histochemistry and transmission and scanning electron microscopy. The primary spermatogonia occupy the periphery of the testis and undergo four mitotic divisions; incomplete cytokinesis results in two secondary, four tertiary and eight quaternary spermatogonia and sixteen primary spermatocytes. The quaternary spermatogonia and successive stages develop in a plasmodial rosette with their nuclei at the periphery and connected to the cytophore by cytoplasmic bridges. The primary spermatocytes undergo two meiotic divisions, resulting in 64 spermatids that develop into spermatozoa. Intranuclear synaptonemal complexes in primary spermatocytes confirm the first meiotic division. The onset of spermiogenesis is marked by an elongation of the spermatid nucleus and the appearance of arching membrane-bound clefts (after Rosario 1964) that delimit the differentiation zone. The latter contains a pair of axonemes with their associated basal bodies and rootlets and, as it extends, the nucleus migrates into it. At first, the axonemes grow at right angles to the extension, but during development they rotate through 90° and come to fuse with the cytoplasmic extension. The mature spermatozoon has a borad head region, a middle piece and a narrow tail region. It consists of a highly coiled nucleus, paired axonemes of the 9+1 pattern typical of platyhelminths, one of which extends the full length of the tail and the other ends part-way along the tail, particles of -glycogen and peripheral microtubules. A crested body spirals around the outside of the sperm body in the tail region.T. acanthiaevulgaris is placed in context within the phylogenetic schemes for cestodes based on sperm ultrastructure.     

A comparative study ofTrilocularia acanthiaevulgaris Olsson 1867 (Cestoda,Tetraphyllidea) from the stomach and spiral valve of the spiny dogfish

Differences in the internal anatomy and ultrastructure ofTrilocularia acanthiaevulgaris from the stomach and spiral valve of the spiny dogfish are described with the aid of electron microscopy and light microscope histochemistry. Worms from the stomach rarely exceed 7 mm in length and do not exhibit signs of segmentation. In contrast, spiral valve worms are segmented, reach a length of some 30 mm and release free proglottides which mature whilst detached from the strobila. Numerous calcareous corpuscles and large glycogen-filled vacuolations occur throughout the body of stomach worms, but are almost totally absent from spiral valve worms. The neck region of spiral valve worms is packed with many germinative cells. The distal tegumental cytoplasm of the stomach worm contains many electron-lucid vesicles, mitochondria and forming microtriches. Microtriches on the tegumental surface are scant, and those present are directed posteriorly. The distal tegumental cytoplasm of the spiral valve worm contains few electron-lucid vesicles and mitochondria but has many dumb-bell-shaped vesicles. Microtriches are longer and more numerous than those of stomach worms. The differences suggest thatT. acanthiaevulgaris worms from the stomach are juveniles which migrate to the spiral valve where they develop into the adult.     

An ontogenetic study of the cholinergic and serotoninergic nervous systems inTrilocularia acanthiaevulgaris (Cestoda,Tetraphyllidea)

The localisation and distribution of the cholinergic and serotoninergic components of the nervous system in the plerocercoid, adult and free proglottis stages of the tetraphyllidean tapewormTrilocularia acanthiaevulgaris were determined by enzyme histochemical and immunocytochemical techniques. The central nerve ring (CNR) in the scolex contains two lateral ganglia and gives rise to five pairs of longitudinal nerve cords (LNC's; three lateral, two median). The nerve cords run posteriorly throughout the bodies of the plerocercoid and adult worms and the free proglottis. Nerves from the CNR and accessory lateral LNC's pass to the bothridia, where they give rise to extensive nerve plexuses. As the individual proglottides develop along the strobila, a small nerve ring forms at the anterior end of each proglottis; within the nerve ring, distinct bilateral ganglia develop prior to the release of the proglottis. All ten LNC's are present in the free proglottis. The genital atrium and cirrus sac are innervated by cholinergic and serotoninergic elements. The cholinergic nervous system predominates in the CNS within the scolex, whereas there is a larger population of 5-HT-immunoreactive nerve cells associated with the LNC's and segmental ganglia along the strobila and within the free proglottis.     

The structure,composition, formation and possible functions of calcareous corpuscles in Trilocularia acanthiaevulgaris Olsson 1867 (Cestoda,Tetraphyllidea)

Mature calcareous corpuscles in the juvenile (stomach) worms of Trilocularia acanthiaevulgaris comprise a number of concentric lamellae interspersed with areas of flocculent material. Each lamella is composed of a pair of membranous rings to which amorphous, non-crystalline material is attached. The process of corpuscle formation is intracellular, beginning with the autophagic breakdown of the cytoplasm to produce a central vacuole within a parenchymal cell. The vacuole enlarges until only a thin layer of cytoplasm remains at the periphery and the nucleus is displaced to one end of the cell. Paired, concentrically arranged membranes are laid down beneath the peripheral cytoplasmic layer and eventually occlude the central vacuole. X-ray analysis of the corpuscles indicates the presence of calcium, phosphorus, sulphur, zinc and molybdenum, with the major peaks representing calcium, phosphorus and sulphur. Calcium appears to be bound to the lamellae rather than associated with the material between lamellae. The possible functions of the corpuscles are discussed in relation to the biology of T. acanthiaevulgaris and its developmental sequence in the dogfish gut.     

The fine structure and possible functions of scolex gland cells inTrilocularia acanthiaevulgaris (Cestoda,tetraphyllidea)

The ultrastructure of the scolex glands ofTrilocularia acanthiaevulgaris is described with the aid of transmission electron microscopy. The syncytial scolex gland cells exhibit an ultrastructure which is typical of secretory cells, in that they contain extensive and distended cisternae of granular endoplasmic reticulum (GER), numerous Golgi complexes and secretory vesicles. The vesicles are transported via microtubule-lined ducts to the apex of the scolex where they are released from the tegumental surface by an eccrine process. The secretion is often accumulated in reservoirs created by a lateral swelling of the ducts. Cytochemical studies show that the secretion has a glycoprotein nature. It is suggested that the secretion probably acts as an adhesive, aiding attachment of the worm to the host mucosa. This may be more important in juvenile worms which have less well-developed scoleces.     

Embryonic development of three Cestoda from the genus Acanthobothrium (Tetraphyllidea, Onchobothriidae) (author's transl)]

The embryonic development from the egg to the oncosphere is examined in three Cestoda: Acanthobothrium coronatum (Rud., 1819), Acanthobothrium filicolle, Zschokke, 1888 and Acanthobothrium zschokkei Baer, 1948 (Tetraphyllidea, Onchobothriidae). The three ontogeneses have in common the following data: -- Two vitelline cells pass with the zygote into the ootype where a thin shell is formed out of a material which comes from the vitelline cells. -- At first the cleavage is equal, then it becomes unequal resulting in the formation of four types of blastomeres: macromere, secondary macromere, mesomere and micromere. -- The preoncospheral phase is characterized first by the blastomere multiplication and later by their decreasing number and differentiation. -- The embryonic envelopes are formed within the shell. The vitelline layer includes the cytoplasm, a vitelline nucleus and possibly the secondary macromere, the nucleus of which always lies against the outer membrane of this envelope. The syncytial embryophore develops from mesomeres coming from the embryo. -- The oncosphere is limited by its owm membrane whose posterior region seems to double in order to form a kind of cap bending over the six hook tips. The final number of embryonic hexacantha cells is relatively low.     

Ultrastructure of the spermatozoon of <Emphasis Type="Italic">Calliobothrium verticillatum</Emphasis> (Cestoda,Tetraphyllidea, Oncobothriidae)

The ultrastructure of the spermatozoon of Calliobothrium verticillatum (Cestoda, Tetraphyllidea, Oncobothriidae) parasite of the smoothhound shark, Mustelus mustelus L. (Pisces, Carcharhiniformes), was studied by transmission electron microscopy. This spermatozoon presents five regions characterized by several ultrastructural elements: an apical cone, a crested body, two axonemes of 9 + “1” pattern, electron-dense granules, a nucleus and cortical microtubules. In the present study, three of these features were the subject of a detailed attention. The first is the presence of two axonemes, which confirms that the Tetraphyllidea, Oncobothriidae possess two axonemes whereas the Tetraphyllidea, Phyllobothriidae possess only one axoneme. The second is the presence of one crested body, a criterion homogeneous in the Tetraphyllidea but heterogeneous among the different orders of Cestoda. The third is the number and the disposition of cortical microtubules. These three criteria seem to be interesting for phylogeny.     

An ultrastructural study of the cirrus and vagina ofPhyllobothrium vagans (Cestoda: Tetraphyllidea)

Ultrastructural observations on the genital ducts ofPhyllobothrium vagans revealed that the lining of both cirrus and vagina is made up of a distal cytoplasmic layer, similar to the tegument, and is lined with microtriches. Microtrichial polymorphism was found in the lining of the cirrus. The ultrastructure of the glandular cells surrounding cirrus and vagina, and of the cirrus sac is described. The significance of the findings to earlier studies on microthrix structure and function as well as to early histological studies of the genital ducts of cestodes is discussed.     

Ultrastructure and cytochemistry of vitellogenesis in Wenyonia virilis Woodland, 1923 (Cestoda, Caryophyllidea)

Vitellogenesis in Wenyonia virilis was examined by transmission electron microscopy (TEM), including the cytochemical detection of glycogen at the ultrastructural level with the periodic acid-thiosemicarbazide-silver proteinate (PA-TSC-SP) technique. Mature vitelline follicles have cells in various stages of development, progressing from immature cells of gonial type near the periphery of the follicle to maturing and mature vitellocytes towards the centre. Maturation is characterized by: (1) increase in cell volume; (2) increase in nuclear surface area restoring the N/C (nucleo-cytoplasmic) ratio; (3) nucleolar transformation; (4) extensive development of parallel cisternae of GER, the shell-protein producing units; (5) development of Golgi complexes, engaged in shell-granule/shell-globule formation and packaging; (6) synthesis and storage of glycogen in the cytoplasm; (7) simultaneous, independent formation and storage of intranuclear glycogen; (8) continuous fusion of small shell-granules into larger shell-globules and fusion of these into large shell-globule clusters with a progressive increase in the number and size of the latter; and (9) disintegration of GER in the medial layer of vitellocyte cytoplasm, degenerative changes and accumulation of glycogen and shell-globule clusters within the cytoplasm. The functional significance of numerous shell-globule clusters and the relatively small amount of nuclear and cytoplasmic glycogen is analysed. Unlike vitellogenesis of other caryophyllids, the nuclear glycogen of mature vitellocytes in W. virilis is randomly dispersed in the nucleoplasm and never forms a high central accumulation, the so-called “nuclear vacuole”. The nutritive function of vitellocytes appears greatly reduced in W. virilis, a fact perhaps related to the intrauterine development of the early embryos. The ultrastructure of vitellogenesis in W. virilis is compared with that in other lower cestodes, both monozoic and polyzoic. Conclusions concerning interrelationships of the vitellogenesis pattern of the ultrastructural cytochemistry of mature vitellocytes of W. virilis to intrauterine embryonation, absence of uterine glands and an extensive uterus characteristic for this species, are drawn and discussed. Dedicated to the memory of Professor Wincenty L. Wiśniewski on the occasion of 50th anniversary of his death     

Ultrastructure of spermiogenesis and mature spermatozoon of Angularella beema (Clerc, 1906) (Cestoda, Cyclophyllidea, Dilepididae)

The ultrastructure of the spermiogenesis of a dilepidid cestode species is described for the first time. The spermiogenesis of Angularella beema is characterised by absence of both flagellar rotation and proximodistal fusion. The differentiation zone is surrounded by cortical microtubules and is delimited by a ring of arching membranes. It contains two centrioles, one of which develops the axoneme that grows directly into the elongating cytoplasmic protrusion. This pattern of spermiogenesis was described as the Type IV spermiogenesis of cestodes. Among cestodes, similar pattern of spermiogenesis is known in the family Hymenolepididae and in some representatives of the family Anoplocephalidae. The mature spermatozoon of A. beema consists of five regions differing in their ultrastructural characteristics. It is characterised by the presence of cortical microtubules (spirally arranged at angle of 30–40° to the spermatozoon axis) and a single crested body. There is a periaxonemal sheath in certain parts of the spermatozoon as well as glycogen-like granules between the periaxonemal sheath and the cortical microtubules. The comparisons of the mature spermatozoon of A. beema with those of other two dilepidid species (Dilepis undula and Molluscotaenia crassiscolex) demonstrate some variation within the family: presence of periaxonemal sheath in A. beema and D. undula and its absence in M. crassiscolex; presence of electron-dense rods in D. undula and their absence in A. beema.     

Molecular identification larvae of Onchobothrium antarcticum (Cestoda: Tetraphyllidea) from marbled rockcod,Notothenia rossii,in Admiralty Bay (King George Island,Antarctica)

Antarctic bony fishes are infected with cestode larvae belonging to the order Tetraphyllidea (parasites as adults in chondrichthyans). Larvae of the Tetraphyllidea differ from each other in the morphology of their scoleces and represent five forms. There are larvae with bothridia subdivided into one, two and three loculi, bothridia sac-like in shape and bothridia undivided with hook-like projections. Only one species of the family Onchobothriidae, Onchobothrium antarcticum, has been described from Antarctica and larvae with trilocular bothridia were assigned to this cestode species. In this study, ten larvae obtained from Notothenia rossii and three adult specimens of Onchobothrium antarcticum isolated from Bathyraja eatonii were examined. A partial sequence of cytochrome c oxidase subunit 1 of three adult specimens and four larvae was identical. The remaining six larval sequences differed from the sequences obtained from adult cestodes. Partial sequences of lsrDNA of all analyzed larvae were identical. These results confirm the taxonomic affiliation of the larvae with trilocular bothridia parasitizing marbled rockcod in Antarctica as Onchobothrium antarcticum.     

Ultrastructure of the spermatozoon of the bank vole tapeworm, Paranoplocephala omphalodes (Cestoda, Cyclophyllidea, Anoplocephalidae)

The mature Paranoplocephala omphalodes spermatozoon is filiform, tapered at both ends and lacks mitochondria. Its anterior extremity exhibits an apical cone of electron-dense material measuring about 900 nm in length and 200 nm in width, and two crested-like bodies. The cortical microtubules follow a 25–35° helicoidal path along their whole length, except at the posterior extremity where they become parallel to the spermatozoon axis. They are arranged in a single or two fields which may cover each other partially. The axoneme, of the 9+“1” pattern of the Trepaxonemata, lacks a peri-axonemal sheath and does not reach the extremity of the spermatozoon. The nucleus is a compact and irregular cord coiled in a spiral around the axoneme. Moreover, we report for the first time a nucleus in the spermatozoon of a Cyclophyllidea species which reaches beyond the axonemal posterior extremity. The cytoplasm, depending on the level where the section is cut, is slightly electron dense or electron lucent and contains numerous small electron-dense granules in regions III–V. In the posterior spermatozoon extremity, granular material is replaced by a terminal and compact electron-dense material. Received: 1 June 1997 / Accepted: 20 September 1997     

Ultrastructure studies of Proteocephalus longicollis (Cestoda, Proteocephalidea): transmission electron microscopy of scolex glands

The ultrastructure of two types of secretory glands in the scolex of preadults of Proteocephalus longicollis is described for the first time in the present report. The gland cells contain extensive cisternae of granular endoplasmic reticulum and Golgi complexes, which participate in the production of secretory globules. Type I scolex glands produce electron-dense globules of various size. The secretory globules enter the secretory canal, openings of which were not observed in the preadults. The secretory product of type I was found at the inner sucker surface and in the tegument of the sucker edges. In addition, electron-dense globules in adult worms are secreted via an eccrine mechanism. Type II scolex glands are characterized by secretory globules of lower electron density and occur mainly in preadults. The electron-lucent, membrane-bound secretory globules are transported via microtubule-lined ducts opening to the exterior at the tegumental surface. Secretory globules of type II are released by an eccrine process. Received: 7 February 2000 / Accepted: 2 March 2000     

Ultrastructure of spermiogenesis and mature spermatozoon of Breviscolex orientalis (Cestoda: Caryophyllidea)

Spermiogenesis and spermatozoon ultrastructure of the caryophyllidean cestode Breviscolex orientalis Kulakovskaya, 1962, first member of the family Capingentidae studied, a parasite of cyprinid fish Abbottina rivularis, are described using transmission electron microscopy. Spermiogenesis in B. orientalis follows the Type II pattern described by Ba and Marchand (Mém Mus Natl Hist Nat 166:87–95, 1995) for cestodes. It begins with the formation of a zone of differentiation containing a large nucleus and a pair of centrioles. The centrioles are separated from one another by an intercentriolar body composed of three electron-dense layers. Each centriole is associated with typical striated roots. At the beginning of the spermiogenesis, an electron-dense material is observed in the apical region of the differentiation zone. During the initial stage of spermiogenesis, one of the centrioles gives rise to a free flagellum, which then rotates and undergoes proximodistal fusion with the cytoplasmic protrusion of the differentiation zone. The mature spermatozoon of B. orientalis corresponds to the Type III pattern described by Levron et al. (Biol Rev 85:523–543, 2010). It is characterized by the absence of mitochondrion and crested body. Five regions of the mature spermatozoon are differentiated. The main ultrastructural characteristics are: one axoneme of 9 + “1” trepaxonematan pattern, cortical microtubules and nucleus. The comparison of the spermiogenesis of B. orientalis with those of the other caryophyllidean species demonstrates some variation within the order relative to the presence and morphology of the intercentriolar body, the presence of slight rotation of the flagellar bud and a complete proximodistal fusion of the free flagellum with a cytoplasmic protrusion.     

Ultrastructure studies on the papillae and the nonciliated sensory receptors of adultSpirometra erinacei (Cestoda,Pseudophyllidea)

The small numerous papillae on the ventral surface of the gravid proglottid of adultSpirometra erinacei were studied by scanning electron microscopy. The arrangement of clumps of papillae was recognized on the surface of the central portion around the genital atrium, with lateral clumps being located above a pair of longitudinal nerve cords and marginal ones, on both sides of the proglottid. By transmission electron microscopy, two types of nonciliated sensory receptors were observed within the papillae. The type I, single receptor was embedded within a papilla. This dome-like sensory receptor contained two electron-dense collars and four rootlets surrounded by numerous thin filaments. The type II receptor was found arranged in groups in the area between the papillae, and the apical end was exposed to the external environment. This simple, club-like sensory receptor contained electron-lucent vesicles and microtubules. We believe that the papillae play an important role in crossinsemination.     

Ultrastructure study of the excretory system and the genital primordium of the infective stage ofOnchocerca volvulus (Nematoda:Filarioidea)

The electron microscopic investigation of the anterior part of the infective third-stage juvenile ofOnchocerca volvulus provides first insights into the structure of the excretory system of this developmental stage of the parasite. The most anterior part of this system consists of a cell process of the syncytial excretory cells. At this height the excretory cells enclose the cuticle-lined excretory channel. The channel is in the process of elongation in the anterior-posterior direction, indicated by cell division in this region. More posteriad an ampulla-like structure is forming in the cytoplasm of the excretory cells. The inner surface of this ampulla is lined with a small number of single microvilli. In this part of the system the cytoplasm of the excretory cells is rich in Golgi bodies and endocytic vesicles. The ampulla has direct access to the exterior by the excretory duct. The excretory duct is a cuticle-lined structure surrounded by supporting fibres of an additional cell. This duct cell connects the excretory duct to the body-wall cuticle at the excretory pore. Adjacent to the region of the excretory system a cell is found that resembles a gland cell. This cell is in close contact to the ventral nerve cord. The genital primordia of the third-stage juvenile consist of several dividing cells. The female genital primordium is seen at the junction of the muscular with the glandular oesophagus and the male primordium can be found at the junction of the glandular oesophagus with the gut.     

Ultrastructure of spermiogenesis and the spermatozoon of Sudarikovina taterae (Cestoda, Cyclophyllidea, Anoplocephalidae) intestinal parasite of Tatera gambiana (Rodentia, Gerbillidae)

The young spermatid of Sudarikovina taterae exhibits a nucleus with a partially condensed chromatin and a differentiation zone, bordered by cortical microtubules, delimited at the front by arched membranes and containing two centrioles. The latter are parallel to one another and linked together at their bases by electron-dense material. During spermiogenesis, one of the centrioles gives rise to a flagellum whereas the other disappears. Crested-like bodies lie outside the cortical microtubules and the nucleus migrates in the spermatid along the axoneme. At the end of spermiogenesis, the ring of arched membranes constricts and the old spermatid becomes detached from the residual cytoplasm. The S. taterae mature spermatozoon is filiform and tapered at both extremities. It exhibits an apical cone of electron-dense material and seven crested-like bodies 50 to 100 nm thick. The cortical microtubules run along the whole length of the spermatozoon. They are spiralized at their anterior extremities and straight over the rest of their length. The nucleus is a fine compact cord interposed between the axoneme and the cortical microtubules. The cytoplasm is slightly electron-dense in regions I and II of the gamete. In regions III, IV and V, it contains fine electron-dense granulations and patches of electron-lucent material. An electron-dense material located both between and under centrioles has not been observed before in a platyhelminth. Similarly, distinctive ultrastructural characters between centrioles and seven crested-like bodies have not been previously described in a cestode. Moreover, we report for the first time the existence of cortical microtubules spiralized only at their anterior extremities in a cestode from a mammal.     

Ultrastructure studies of preadult Proteocephalus longicollis (Cestoda, Proteocephalidea): transmission electron microscopy of scolex sensory receptors

The ultrastructure of five types of presumed sensory receptors in the scolex of preadults of Proteocephalus longicollis is described. Two types of nonciliate sensory receptors are situated on the inner surface of the lateral sucker. They differ from each other in the shape, presence, or absence of a large rootlet, electron-dense collars, desmosomes, microtubules, and/or vesicles. In addition, three types of ciliate sensory receptors are found along the edges of the lateral suckers. They can be differentiated by the length of the cilium, by the number of electron-dense collars (one or two), and by types of vesicles. Four types of vesicles were found inside the ciliate sensory receptors. One type of ciliate sensory receptor occurring in preadults differs markedly from any of the sensory receptors previously described in adult P. longicollis. Received: 18 June 1999 / Accepted: 28 July 1999