Comparison of the Benzanthrone Luminophores: They Are Not Equal for Rapid Examination of Parafasciolopsis fasciolaemorpha (Trematoda: Digenea)

Luminescent derivatives of benzanthrone are becoming more useful based on their light-absorbing and fluorescent-emitting properties. Our previous studies showed that luminescent staining properties of the same benzanthrone dye differ for variable parasite samples. Therefore, two types of benzanthrone dyes were prepared. One has a strongly basic amidine group and a halogen atom, and the other has an amide moiety and a tertiary amine group. Trematoda Parafasciolopsis fasciolaemorpha is a liver fluke of a moose (Alces alces) and has a significant influence on the health and abundance of the moose population. Staining protocols for parasite P. fasciolaemorpha specific organ or organ systems imaging are mostly time-consuming and labor-intensive. The study aimed to compare the fixation technique and the staining protocol by synthesized benzanthrone luminescent dyes to determine detailed morphology, anatomical arrangement of the organ systems and gross organization of the muscle layers of P. fasciolaemorpha using confocal laser scanning microscopy. Luminophores were tested for samples fixed in different fixatives. Developed dyes and staining protocol resulting in imaging of all parts of trematode without additional sample preparation procedures, which usually are required for parasite examination. Obtained results confirmed that the most qualitative results could be reached using 3-N-(2-piperidinylacetamido)benzanthrone dye which has amide moiety and a tertiary amine group. Based on obtained results, 3-N-(2-piperidinylacetamido)benzanthrone gave more qualitative parasite visualization than 2-bromo-3-N-(N′,N′-dimethylformamidino)benzanthrone.

Functional ultrastructure and cytochemistry of vitellogenesis and mature vitellocytes of the digenean Cainocreadium labracis (Dujardin, 1845), parasite of Dicentrarchus labrax (L., 1758)

Vitellogenesis and vitellocytes of Cainocreadium labracis were studied by transmission electron microscopy (TEM) and TEM cytochemistry. Four developmental stages were distinguished during vitellogenesis: (I) stem cell of high nucleo-cytoplasmic ratio; (II) early differentiation with chief activity focused on the beginning of protein synthesis and shell globule formation; (III) advanced differentiation with rapid intensification of protein synthesis, progressive fusion of single shell globules into large globule clusters, and formation of unsaturated lipid droplets surrounded by β-glycogen particles; and (IV) mature vitellocyte. Early vitellogenesis with vitellocyte maturation consists of: (1) increase in cell volume; (2) increased development of large, parallel cisternae of GER with production of proteinaceous granules; (3) development of small Golgi complexes that package granules; and (4) within vacuoles, progressive enlargement of proteinaceous granules into shell globule clusters formed during vitellogenesis. Three types of inclusions accumulate in large amounts in mature vitelline cells: (1) shell globule clusters, important component in the formation of egg shell; (2) numerous unsaturated lipid droplets. Though fewer, there are also diphasic droplets consisting of saturated and unsaturated lipids in the same droplet, and (3) a relatively small amount of β-glycogen particles, usually surround a few groups of lipid droplets. The β-glycogen and lipid droplets are nutritive reserves for embryogenesis. General pattern and functional ultrastructure of vitellogenesis greatly resemble those observed in some lower cestodes, such as bothriocephalideans and diphyllobothrideans. Variations and differences in the amount of lipids and of glycogen during vitellogenesis in lower cestodes and other trematodes are compared and discussed.

Advances in Spermatological Characters in the Digenea: Review and Proposal of Spermatozoa Models and Their Phylogenetic Importance

The wide biodiversity and economic importance of digeneans have motivated a great deal of research in the last decade, focussing on their phylogenetic positions. Molecular research was instrumental for our understanding of phylogeny in the Digenea, but spermatological studies have also provided many results, which are potentially useful for phylogeny; however, the complete spermatological data set has never been reviewed in a whole phylogenetic perspective. Spermatological data are now available for more than 100 species, belonging to 15 superfamilies and 46 families. In this paper, we try to summarize the current knowledge about sperm structure in the digeneans and propose a classification of digenean spermatozoa into five basic models. The main ultrastructural characters used are (1) the type of axoneme, (2) the lateral expansion, (3) the association 'external ornamentation of the plasma membrane + cortical microtubules', (4) the field of cortical microtubules and its number, (5) the location of the external ornamentation, (6) the location of the maximum number of cortical microtubules and (7) the number of mitochondria. We also outline the most interesting features for phylogenetic inference and their possible value in the context of digenean systematics, phylogeny and evolution. Associations between sperm models and superfamilies were found as follows: Type 1 in the Schistosomatoidea; Type 2 in the Hemiuroidea; Type 3 in the Opecoeloidea, Lepocreadioidea, Haploporoidea and Opisthorchioidea; Type 4 in the Gorgoderoidea, Microphalloidea, Plagiorchioidea and Gymnophalloidea; Type 5 in the Echinostomatoidea, Microscaphidioidea, Paramphistomoidea, Pronocephaloidea and Brachylaimoidea.

Ultrastructural evidence for completion of the entire miracidial maturation in intrauterine eggs of the digenean Brandesia turgida (Brandes, 1888) (Plagiorchiida: Pleurogenidae)

Results of this TEM study provide ultrastructural evidence that miracidial morphogenesis is fully completed within the intrauterine eggs situated in the most posterior uterine regions of the pleurogenid trematode Brandesia turgida (Brandes, 1888). The ultrastructural characteristic of different larval organelles and cell types of these eggshell-enclosed, but fully formed, cilated miracidia is described. The body wall of the pyriform mature miracidium of B. turgida is composed of ciliated epidermis and underlying peripheral body musculature. Two miracidial flame cells of the protonephridial excretory system are localized in the central region of the ciliated larvae. Three types of miracidial glands were observed: a single apical gland, two lateral glands, and several small vesiculated glands; each gland type contains characteristic, but different types of secretory granules. The anterior end of each miracidium consists of an apical papilla on which are situated the exits of the three main larval glands: an exit of a single apical gland as well as the individual exits of two lateral glands. The exits of vesiculated glands, containing characteristic spherical membrane-bound and highly electron-dense granules, evidently different from the two other types of secretory granules of apical and lateral glands, were not identified. Germinative cells, grouped together in a sac-like germinative follicle, are situated in the medioposterior part of the larva, the germatophore. The germinative cells contain numerous electron-dense heterochromatin islands arranged in the form of a network or chain-like pattern and distributed mainly in the karyoplasm adjacent to the nuclear membrane. The thin layer of granular cytoplasm is rich in free ribosomes and contains a few small mitochondria. Both nuclear and cytoplasmic features if these cells indicate their great developmental potential for further growth and multiplication in postembryonic stages of the life cycle. In the mature eggs, the areas of focal cytoplasmic degradation were frequently observed and may be involved in the autolysis of some embryonic structures. Obtained results are compared with available literature data on the functional ultrastructure of the miracidia of other digeneans.

[Reproduction of trematode Leucochloridium paradoxum sporocysts (Trematoda: Leucochloridiidae)]

The histological study of the trematoda sporocysts Leucochloridium paradoxum confirmed the presence of three morphological zones in it: 1) central part (reproductive), where embryos are forming, 2) narrow tubes through which the embryos penetrate in colored broodsacs (3), where the development of metecercaria completes. It was found that germinal mass only is the reproduction organ of the sporocysts, located in reproductive zone. There are young (without embryos), mature (with embryos) and degenerated germinal masses. So, in the process of sporocysts development the centre of multiplication of germinal elements was changed. The old parts of central part are degenerated, but the new ones with young germinal masses appear. The multiplication of generative elements does not take place in the broodsacs which are breeding cameras functionally.

Spermatozoon ultrastructure of Gyliauchen sp. (Digenea: Gyliauchenidae), an intestinal parasite of Siganus fuscescens (Pisces: Teleostei)

The ultrastructure of the mature spermatozoon of Gyliauchen sp., a parasite of the dusky rabbitfish Siganus fuscescens, was studied by transmission electron microscopy. The spermatozoon possesses two axonemes of the 9+"1" pattern of Trepaxonemata, four attachment zones, one mitochondrion, a nucleus, cortical microtubules, external ornamentation of the plasma membrane, and spine-like bodies. The main characteristics of this spermatozoon are the presence of one mitochondrion, spine-like bodies not associated with the external ornamentation, and a posterior extremity of type 3 that is characterized by the following sequence: posterior extremity of the nucleus then posterior extremity of the second axoneme. Numerous other ultrastructural features are also discussed and compared to the digenean spermatology literature. This is the first study of a member of the Gyliauchenidae and the fourth within the Lepocreadioidea. The results show that many ultrastructural characters are variable within this superfamily and could be useful for phylogeny.

Actitis hypoleucos (L., 1758)--new Polish host of the trematodes: Plagiorchis nanus (Rudolphi, 1802) and Leucochloridium perturbatum Pojmańska, 1969

In July-August of 2005-2008, 47 digenean trematodes were examined from 7 specimens of the common sandpiper, Actitis hypoleucos (L., 1758). The digeneans were collected during a study on the food composition of the common sandpiper. The research was conducted near Lisewo Malborskie (near Tczew, Zuławy Wiślane, Gdańsk sea-coast), at a resting site on the birds' migration route. The foods ingested were extracted from live birds by draining their alimentary tracts with a nasogastric tube. Two digenean species were identified: Plagiorchis nanus Rudolphi, 1802 (Plagiorchiidae) and Leucochloridium perturbatum Pojmańska, 1969 (Leucochloridiidae). Actitis hypoleucos is the host for these new records in Poland. The P. nanus individuals isolated from A. hypoleucos differed in terms of the visible uterus and the extent of the vitellaria in the posterior part of the body.

Cellular aspects of early development of Ornithodiplostomum ptychocheilus metacercariae in the brain of fathead minnows, Pimephales promelas

Trematode metacercariae typically are regarded as nonfeeding and metabolically inactive. However, the metacercariae of many trematode species undergo complex and prolonged periods of development within their intermediate hosts. In the present study, we used electron microscopy to document chronological changes in development of the tegument of Ornithodiplostomum ptychocheilus metacercariae recovered from the brains of experimentally infected fathead minnows (Pimephales promelas). Commencing at 4 days postinfection (PI), the smooth, thin, syncytial tegument transforms into a complex microlamellar and microvillar system that encircles the entire body surface. The microvilli are oriented in parallel in an extended pattern, reaching directly away from the parasite and toward the receding host tissue. The microvilli disappear at approximately 28 days PI, followed by deposition of the cyst wall and further transformation of the tegument into the spinose, a glandular structure typical of an immature adult. To our knowledge, the progressive disaggregation of host cells at the leading edge of elongating parasite microvilli has not been demonstrated previously for any trematode. These results provide morphological evidence that the metacercariae of some trematode species undergo complex developmental changes associated with feeding in their intermediate host.

In vitro excystment of the metacercariae of Ribeiroia ondatrae

In vitro excystation studies were done on the metacercarial cysts of Ribeiroia ondatrae obtained from naturally infected leopard frogs, Rana pipiens. Studies were done in Petri dish cultures in various media maintained at 41 degrees C. The media consisted of 0.5% trypsin-0.5% bile salts in Earle's balanced salt solution at pH 7.8 (TB), 1% acid pepsin (AP) in 0.85% saline adjusted to pH 2 with HCl; acid saline (AS) adjusted to pH 2 with HCl, and saline (S). The TB medium, used successfully to excyst the metacercariae of numerous species of digeneans, did not induce excystation of Ribeiroia ondatrae. Some excystation occurred in AS but not in S. Excystation was 100% in AP with most organisms excysting within 30 s after placement in the medium at 41 degrees C. Excystation in vitro in AP at 41 degrees C is compatible with the fact that this organism establishes itself in the acid-pepsin environment of the proventriculus of avian hosts.

INFORMATION ABOUT TRANSMISSION OPPORTUNITIES TRIGGERS A LIFE-HISTORY SWITCH IN A PARASITE

Many microbial pathogens can switch to new hosts or adopt alternative transmission routes as environmental conditions change, displaying unexpected flexibility in their infection pathways and often causing emerging diseases. In contrast, parasitic worms that must develop through a fixed series of host species appear less likely to show phenotypic plasticity in their transmission pathways. Here, I demonstrate experimentally that a trematode parasite, Coitocaecum parvum, can accelerate its development and rapidly reach precocious maturity in its crustacean intermediate host in the absence of chemical cues emanating from its fish definitive host. Juvenile trematodes can also mature precociously when the mortality rate of their intermediate hosts is increased. Eggs produced by precocious adults hatch into viable larvae, capable of pursuing the parasite's life cycle. In the absence of chemical cues from fish hosts, the size of eggs released by precocious trematodes in their intermediate hosts becomes more variable, possibly indicating a bet-hedging strategy. These results illustrate that parasitic worms with complex life cycles have development and transmission strategies that are more plastic than commonly believed, allowing them to skip one host in their cycle when they perceive limited opportunities for transmission.

Nitric oxide and its target cells in cercaria of Diplostomum chromatophorum: a histochemical and immunocytochemical study

In order to advance our knowledge of the nitrergic nervous system in flatworms, the patterns of the NADPH-diaphorase (NADPH-d) reaction and cGMP immunoreactivity, after stimulation with a nitric oxide donor in the presence of an inhibitor of phosphodiesterase, were investigated in cercaria of Diplostomum chromatophorum. This is the first time the presence of NADPH-d activity has been detected in a larval fluke, and the first time the presence of cGMP immunoreactivity has been detected in a flatworm. The NADPH-d reaction occurs in the ventral sucker, the hind body and the tail. cGMP immunoreactivity was detected in the muscle cells of the body and in two pairs of sensory cells at the anterior end of the body and in the middle of the furca. The sensory cells also showed 5-HT immunoreactivity. The spatial relationship between the cGMP and the 5-HT immunoreactivities was studied. By staining with TRITC-labelled phalloidin, the pattern of the muscle fibres was revealed.

On the systematic position of Ophiosacculus Macy, 1935 (digenea: Lecithodendriidae), with the erection of the Ophiosacculinae n. subfam

The phylogenetic relationships and systematic position of the digenean genus Ophiosacculus Macy, 1935 has been controversial and opinions of different authors on its systematic position and content are contradictory. Molecular analysis based on the partial sequences of the large subunit ribosomal DNA gene of the type and only valid species of the genus, Ophiosacculus mehelyi (Mödlinger, 1930), as well as previously published sequences of members of several families of Plagiorchiata (including the Allassogonoporidae, Lecithodendriidae and Pleurogenidae as potential relatives of Ophiosacculus) has shown that Ophiosacculus forms a clade with the typical representatives of the Lecithodendriidae from bats. Ophiosacculus is basal to the cluster containing Lecithodendrium, Prosthodendrium and Pycnoporus and has quite pronounced differences in the sequenced fragment compared to these genera. Based on the results of the molecular study, morphological characteristics of Ophiosacculus (in particular, possession of a seminal vesicle lying freely in parenchyma) and the fact that the type-specimen of Gyrabascus brevigastrus Macy, 1835 (type-species of the monotypic genus Gyrabascus and type-genus of the subfamily Gyrabascinae) belongs to Allassogonoporus, a new subfamily, the Ophiosacculinae, with Ophiosacculus as the type-genus, is established within the Lecithodendriidae. Molecular study did not support a close phylogenetic relationship between Allassogonoporus and Ophiosacculus, although several authors previously allocated both these genera to the Allassogonoporidae. Morphological study revealed the position of the genital pore in O. mehelyi to be at the posterior margin of the ventral sucker. An amended diagnosis of Ophiosacculus and a diagnosis of Ophiosacculinae n. subfam. are given.

[Parthenogenetic generations of Sanguinicola armata (Trematoda: sanguinicolidae)]

Daughter sporocysts of Sanguinicola armata are represented by several generations, changes of which goes synchronously with the changes of year seasons. Young individuals beginning the reproductions form exclusively cercariae. The old sporocysts begin to produce sporocysts only. These young sporocysts do not quite the organism of the old sporocyst. Therefore, series of sporocysts inside other sporocysts are often observed in hystological cross-sections. Germinal masses of daughter sporocysts of S. armata have some specific characters, which are not observed in analogous organs in daughter sporocysts of other trematode species.

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.

[Contribution to the morphological description of Tylodelphys barilochensis and Tylodelphys crubensis (Trematoda, Diplostomidae) encephalon parasites of Galaxias maculatus (Teleostei, Galaxiidae)]

Taxonomic characteristics, for species identification, of metacercarie of T. barilochensis and T. crubensis found in the encephalon of the fish Galaxias maculatus, not included in the original descriptions, particularly those concerning to the excretory system, are described.

Cytological study of Rubenstrema exasperatum (Trematoda:Omphalometridae)

Cytological studies on Rubenstrema exasperatum were carried out. The number of chromosomes in diploid cells (2n = 16), and the morphological characteristics of the karyotype were determined. All the chromosomes (from Nos 2 to 8) had a well-defined short arm and, in accordance with the Ic values, were determined to be meta-submetacentric. Polymorphism was established in the length of the 2 homologues of the 1st chromosome. This pair is probably linked with sex determination.

Cytochemical localization of cytochrome c oxidase activity in mitochondria in the tegument and tegumental and parenchymal cells of the trematodes Echinostoma trivolvis, Zygocotyle lunata, Schistosoma mansoni, Fasciola gigantica and Paragonimus ohirai

Cytochrome c oxidase in the mitochondria of the tegument and tegumental and parenchymal cells was examined cytochemically in Echinostoma trivolvis, Zygocotyle lunata, Schistosoma mansoni, Fasciola gigantica and Paragonimus ohirai, trematodes that inhabit different sites in their vertebrate hosts. Clear differences in enzyme activity occurred in the mitochondria of these species, probably reflecting the different energy metabolisms of these worms. Marked aerobic metabolism occurred in S. mansoni and P. ohirai adults that inhabit the host mesenteric veins and the lungs, respectively. The tegument and parenchymal cells of S. mansoni possess relatively few, small mitochondria with tabular cristae which are heavily reactive for cytochrome c oxidase. In P. ohirai, the activity for cytochrome c oxidase in tegumental mitochondria increased gradually from juveniles to adults, reflecting that the respiratory activity increased with growth and the aerobic metabolism is activated when the worms reach the lung. P. ohirai juveniles and adults had two types of mitochondria with different shapes and enzyme activities that were located in two different types of parenchymal cells. The intestinal species, E. trivolvis had mitochondria in the basal aspect of the tegument, and some variations in enzyme activity of their mitochondria in the tegumental and parenchymal cells were observed, suggesting that they possess both aerobic and anaerobic metabolic systems. Z. lunata that live in rodent caeca are devoid of mitochondria in the tegument and have many characteristic mitochondria with undeveloped cristae in the parenchymal cells. Mitochondria of F. gigantica showed weak or no activity for cytochrome c oxidase, suggesting that the worm is well-adapted to an anaerobic environment in the host bile duct.

[Transmission electron microscopic ultrastructure of the tegument of Fibricola seoulensis]

An electron microscopic study was performed to observe the ultrastructure of the tegument of F. seoulensis. The outer surface of the tegument was covered with a trilaminated plasma membrane. The electron-dense cytoplasmic layer was 2.5 microns wide in the anterior portion and contained numerous vacuoles, mitochondria and granular materials in its matrix. The basement layer was 330 nm wide or so, and its numerous extensions protruded into the cytoplasmic layer. The sensory organ was composed of a small vesicle of 1.7 x 1.1 microns in dimensions, which possessed a cilium of 1.2 x 0.19 micron in size. The pharynx was composed of the epithelial layer of about 0.5 micron wide, well developed muscle layer and basement layer. The tegument of the oral sucker was composed of a cytoplasmic layer of 0.4-0.5 micron width, a narrow basement layer, a well developed muscle layer and tegumental cells. Some kinds of secretory granules that seemed to be originated from the cells of the oral sucker were observed in the parenchymal portions of the adjacent cells. The tribocytic organ consisted of numerous microvilli. The microvilli were 5 nm wide and heptalaminated. Two types of secretory granules originated from the gland cells of tribocytic organ were observed in the tegument and parenchyme. The tegumental cells were irregular in shape, and of which nuclei were multifarious.

Transmission electron microscopic findings of the tribocytic organ of Fibricola seoulensis

We observed ultra-structure of the tribocytic organ of Fibricola seoulensis with transmission electron microscope. Microvilli are observed on the surface of the tribocytic organ. Below the muscle layer, we can find three types of cells. Type I cell has electron lucent cytoplasm with a few granules, while type II cell shows electron dense cytoplasm and the particulate granules. Type III cell's electron dense cytoplasm possesses many granules. Of the above three cells, Type I and II cells are believed as tegumental cells. Type III cells are thought as glandular cells specific to the tribocytic organ. This finding can also explain the secretory function of the tribocytic organ of F. seoulensis.

Histochemical findings of the tribocytic organ and tegument of Fibricola seoulensis

The tribocytic organ and tegument of Fibricola seoulensis were examined histochemically for the detection of carbohydrates, mucosubstances, amyloid, collagen and alkaline phosphatase. The surface, secretes, gland cells of the tribocytic organ, and the tegument of the worms were positive to periodic acid Schiff (PAS) and PAS with diastase stain but negative to other stains. It was inferred that the tribocytic organ and tegument of F. seoulensis comprise neutral mucopolysaccharides, which may take a protective role against host enzymes. The surface and secretes of the tribocytic organ, and the tegument of the worms were also positive to double bridge PAP for alkaline phosphatase. This fact suggests that they may play a role as both self protective and host tissue lytic functions.

[Hypothesis of the biogeographical origin of Diplozoon (Monogenea, Polyopisthocotylea)]

The evolutionary geographic origin of Diplozoon and Octomacrum (Monogenea, Polyopisthocotylea) is discussed. Diplozoon occurs in Eurasia and Africa, whereas the distribution of Octomacrum is limited to North-America. These two monogeneans likely had a common progenitor originating from the Pacific. This hypothesis is suggested by the morpho-anatomical resemblances between Diplozoon and Octomacrum and by the analysis of their geographic distribution.

Ultrastructural and cytochemical observations of the spherites in a parasite trematoda larva

Concentric laminated concretions, termed 'spherites', were found in the parenchymal cells and in the lumen of the collecting vessels of the trematode Meigymnophallus minutus, parasite of a lamellibranch mollusc. In the initial stage, the spherites are surrounded by a membrane and located in close proximity to the endoplasmic reticulum and Golgi complexes, increasing in size with age and by deposit of concentric layers. Later, they migrate and are released into the lumen of the collecting vessels. These structures contain high concentrations of calcium and phosphorus. The organic matrix is mainly composed of protein, lipids, acid phosphatase and glycoproteins as demonstrated by several cytochemical staining methods. It is possible that these calcareous concretions play an important role in the excretory system of the adult trematode, the life cycle of which takes place within the mantle of the host mollusc.

Report of Episthmium caninum (Verma, 1935) Yamaguti, 1958 (Digenea: Echinostomatidae) in man

The first finding of Episthmium sp. in man is reported. Characteristics of the worm are given in detail. The infestation is an accidental one acquired from consuming raw fish, which serves as an intermediate host of Opisthorchis viverrini. The pathogenic role of Episthmium sp. in man needs further investigations.

Cytochemical characteristics of the neurosecretory cells of Ceylonocotyle scoliocoelium (Trematoda: Digenea)

Two types of neurosecretory cells (NSC), large alpha cells and small beta cells were detected on the basis of their size and characteristics as shown by aldehyde fuchsin and chrome haematoxylin-phloxin staining. A histochemical survey of the neurosecretory material indicates that it is a glycoprotein. Phosphatases and esterases present in NSC probably help in the transfer of metabolites and their hydrolysis and in the control of secretory material produced in a NSC, while SDH provides the necessary energy for the synthetic activity of the latter. The role of neurosecretion in governing the reproduction of this parasite is discussed.

Normal development of Schistosomatium douthitti in the snail Lymnaea catascopium

Schistosomatium douthitti miracidia are ingested by Lymnaea catascopium snails and penetrate the host's esophageal wall. Mother sporocysts develop adjacent to the esophagus and salivary glands. The increase greatly in size, become irregular in shape, and contain daughter sporocysts by 8 days. Development of daughter sporocysts is synchronous; most are released from mother sporocysts 16--20 days postexposure. Mother sporocysts then collapse, but may persist for the life of the infected snail. Some daughter sporocysts travel to the digestive gland via the arterial system; others traverse the connective tissue separating cephalopedal and visceral sinuses to reach the digestive gland. Cercarial embryo production begins while daughter sporocysts are still within mother sporocysts, and may continue for over 400 days. Once released from daughter sporocysts, cercariae move from the visceral sinus to the visceral vein and are carried into the mantle where they rupture the ventral mantle epithelium and escape from the molluscan host.

Taxonomy of Leucochloridium sp. (Digenea) infecting Succinea pfeifferi Rossmässler, 1835

The anatomical and morphological variability of sporocysts and metacercariae of Leucochloridium sp. recovered from natural infected Succinea pfeifferi Rossmässler collected in the Agdenes area. Norway (63 degrees 35'N, 9 degrees 45'E), was studied by light microscopy. The results are compared with five species from the Nearctic and Palearctic with known adult stage (L. variae McIntosh, 1932; L. fuscostriatum Robinson, 1947; L. perturbatum Pojmanska, 1969; L. subtilis Pojmanska, 1969; L. fuscum Rietschel, 1970) and nine species with unknown adult stage. In the larval stages no morphological taxonomical characters were found to separate Leucochloridium sp. as a species distinct from the five (and nine) species. The variability and validity of the characters used is discussed.

[The oncomiracidium of Ancyrocephalus paradoxus Creplin, 1839 (Monongenea, Monopisthocotylea), parasite of Sander lucioperca (Teleostei, Percidae)]

The distribution of ciliated cells and the oncomiracidium chaetotaxy in Ancyrocephalus paradoxus Creplin, 1839 (Ancyrocephalidae) parasite of Sander lucioperca (Teleostean, Percidae) are described for the first time as well as the larval ciliated cells in Dactylogyrus extensus (Dactylogyridae) parasite of Cyprinus carpio. Also is given a description of the larval haptorial armature of Ancyrocephalus paradoxus which shows some original features in our region. The ciliated cell pattern and chaetotaxy are compared among Ancyrocephalus paradoxus (Ancyrocephalidae) Ergenstrema mugilis (Ancyrocephalidae) Dactylogyrus extensus (Dactylogyridae) Tetraonchus menenteron (Tetraonchidae) and Euzetrema knopffleri the systematic position of which is still to be defined. As a result it appears that an unitary pattern occurs in the ciliated cell arrangement and chaetotaxy in the larvae of Ancyrocephalus paradoxus, Ergenstrema mugilis and Dactylogyrus extensus. Yet they are easy to distinguish. Tetraonchus monenteron reveals some affinities with these Dactylogyroïdea but further investigations have to be undertaken again while Euzetrema knoepffleri proves to be very different. In the armature of the larval haptor of Ancyrocephalus paradoxus intraspecific variations appear which seem to be of a biogeographic order. Also the same variations are reported in the larvae of Diplectanum aequans.

Cell cycle analysis in developing cercariae of Trichobilharzia ocellata (Trematoda: Schistosomatidae)

Cellular proliferation has been analyzed during cercarial development of the digenetic trematode Trichobilharzia ocellata. Prior to the tail-bud stage (about 1,000 cells), cells were actively involved in cellular proliferation. The mean cell cycle was 15.2 hr. The time for mitosis was 1.6 hr; for G1, 5.6 hr; for G2, 3.2 hr, and for the S phase, 4.8 hr. Beginning with the tail-bud stage, an increasing proportion of cells accumulate in the G1 phase. Cytological evidence of changes in the amount of cytoplasm per cell revealed that these noncycling cells were differentiating. During organ development and differentiation, the proportion of proliferating cells decreases and by the 2,000-celled stage proliferation ceases. Our results do not support a germinal lineage theory of cercarial development since none of the observed nuclear types could be unequivocally identified as belonging to the germ line.

Relationship between nuclear morphology and the phases of the cell cycle during cercarial development of the digenetic trematode Trichobilharzia ocellata

During the proliferative phase of cercarial development in the digenetic trematode Trichobilharzia ocellata, nuclei varied in size, appearance of the chromatin, and intensity of Feulgen staining. On the basis of interphase nuclear morphology six nuclear classes were identified. Data from microspectrophotometric determinations and 3H-TdR labeling experiments were used to correlate each kind of interphase nucleus with a phase of the cell cycle. Marked variability in nuclear area developed between cells by time they reached late G1. Increases in nuclear area could not be correlated with the onset of DNA synthesis. Throughout all stages of development of T. ocellata cercariae, proliferating cells divide mitotically; meiotic divisions were never seen. Thus, the mode of reproduction appears to be asexual. No evidence was found to support previous suggestions of diploid parthenogenesis.

[Isolation of the cercaria Diplostomum phoxini (Faust, 1918) Arvy et Buttner, 1954 (Diplostomatidae) from fresh water mollusks of the Crimea]

Data on the biology and morphology of cercariae of Diplostomum phoxini (Faust, 1918) Arvy et Buttner, 1954 are given. The cercariae were found in Radix auricularia from the middle part of the Burulcha river (Ukranian SSR, Crimea). In November, 1974 the invasion extensity of mollusks was 16.3%. No cercariae were found in spring and summer samples.

Miracidium of Allocreadium fasciatusi Kakaji 1969 (Trematoda: Allocreadiidae)

The miracidium of Allocreadium fasciatusi has 18 epidermal cells arranged in 3 tiers according to the formula 6,8,4. In the posterior part of the miracidium there is a fully formed redia while the anterior part contains 2 fluid-filled refractile sacs which appear to store the waste material released by the redia. The 2 excretory pores of the miracidium are middorsal and midventeral rather than lateral.

An electron microscope study of the tegument of the metacercaria and adult of Leucochloridiomorpha constantiae (Trematoda: Brachylaemidae)

The tegumentary ultrastructure of Leucochloridiomorpha constantiae metacercariae and adults has been described. A filamentous glycocalyx invests the tegument of metacercariae and large numbers of biconcave, disk-shaped secretion vesicles are found in its outer zone, cytoplasmic bridges and cytons. Mitochondria within the outer tegumentary zone of metacercariae are restricted to its basal half. The transformation of metacercariae to adults involves the loss of the glycocalyx, a decrease in the number of disk-shaped secretion vesicles, a more uniform distribution of mitochondria through the outer tegumentary zone, an apparent degeneration of cytons, a thinning of the fibrous basal lamina and a decrease in the number of visible cytoplasmic bridges traversing it. The significance of these events for a metacercaria which does not encyst within the molluscan host is discussed. In addition, crystalline, spine-like inclusions in the outer tegumentary zone of adult L. constantiae are described and their possible function discussed.

Light and scanning electron microscopy of attachment organs of three monogeneans (Monogenoidea: Polyopisthocotylea)

The anterior and posterior attachment organs of three species of monogeneans, Diclybothrium armatum Leuckart, 1835, Neodiscocotyle carpioditis Dechtiar, 1967, and Mazocraeoides olentangiensis Sroufe, 1958, were examined in whole-mount light-microscope preparations, and by scanning electron microscopy (SEM). Bothria with openings of gland cells were identified anterior to the oral opening in D. armatum, but sucker-like units evident in light microscopy were not seen by SEM in N. carpioditis and M. olentangiensis as these are apparently internal developments. Holdfast units of the opisthaptor of the three species are of three distinct forms: spring-like clamps in D. armatum, muscular clamps in M. olentangiensis. and suckers with sclerotized rims in N. carpioditis. Hooks in the opisthaptor appendage of D. armatum all function to form a C-shaped double-pronged hook unit. Two of the three pairs of hooks in the posterior end of M. olentangiensis project slightly from the body, while the third pair in this species and the single pair of hooks in N. carpioditis are entirely internal, probably non-functional and vestigial.