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A study of 94 slugs, collected from urban and rural areas in and around Léon, Nicaragua, was carried out in order to confirm the role of Vaginulus plebeius as an intermediate host of Angiostronglylus costaricensis. Third-stage larvae of A. costaricensis were obtained from these molluscs. Some of these larvae were then orally inoculated into two laboratory-bred rats Sigmodon hispidus and adult worms of A. costaricensis were recovered two months later. The infection rate of these slugs ranged from 4% in urban areas to 85% in rural areas. These data suggest that contamination to man is a major risk especially in rural areas and that abdominal angiostrongyliasis could be a health problem in Nicaragua.

The authors point out the ecological conditions required for the life-cycle development of Maritrema misenensis (A. Palombi, 1940). This Microphallid parasite occurs in waveless lagoons as well as along the waved marine coast. The first and second intermediate hosts found in these two habitats are not alike. Along the calm edges of the lagoon edges Cerithium mediterraneum (first host) and Orchestia mediterranea (second host) are found whereas along the rocky sea-coast C. rupestre (first host) and O. montagui (second host) are to be seen. The first intermediate hosts are heavily infected along the margin of the lagoon; the parasitism is decreasing gradually as we go away the edge. The infection of the second host depends on the behaviour both of Orchestia and cercariae. Numerous cercariae accumulate against along the very edge of the lagoon, exactly where Orchestia enter the sea-water. The Orchestia parasitism varies as you go along the coast and according to the seasons; it is also different whether you are dealing with males or females.

This 9th Contribution concerns Cestodes obtained from: A Lamellibranchiata, B Gastropoda, C Pteropoda, D Cephalopoda, E Crustacea.

Pseudoleucochloridium soricis develops to the sporocyst stage in the digestive gland of the terrestrial Pulmonate Cepaea hortensis. The cercaria, microcercous in type, is liberated and actively penetrates a second terrestrial pulmonate where development to the free metacercarial stage takes place in the pericardial cavity. Ecologically, the cycle of P. soricis in the Pyrenees, exhibits two characteristics which require particular attention: --the transmission of the parasite to the second host, which, although experimentally possible, and with equal success, in two species of Helicide (C. hortensis and Euomphalia strigella) occurs in the wild preferentially in E. strigella. The differing trophic behaviour of the two molluscs is thought to be the factor responsible for this selection;--the level of infection in shrews appears to be extremely low (never more than 1%) in all sampling areas, a character which contraste with the persistantly high level of infection in the second host (at least 50%). This epidemiological character points to the probable evolution of P. soricis in a definitive host (almost certainly a Bird) which has not yet been discovered.

The cercarial index defined by Bayssade-Dufour (1977) differs according to the hosts in which Schistosoma mansoni is cycled. This index is close to 1 in African human strains, 1.3 in Carribbean human strains, and 1.6 in strains kept for a number of years in rodents. The first epidemiological and experimental results supported the argument that the transmission of intestinal bilharzia in the mountainous refuge of infection at Grand-Etang, Guadeloup, is maintained exclusively by murine rodents. New epidemiological and experimental data lead us to believe that the black rat of Guadeloup is an inadequate host for S. mansoni, incapable of maintaining the parasite beyond a few cycles.

The life cycle of a Paramphistome from North Senegal is completed starting from cercariae shed by naturally infected Isidora guernei: a sheep and then uninfected Isidora guernei were successively infected experimentally. Adults obtained were identifiable as P. phillerouxi or as P. microbothrium. Species determination cannot be made on the basis of argentophilic structures in the miracidium. Morphology of sporocysts and rediae differs from that observed in P. phillerouxi but is undistinguishable from that described in P. microbothrium. Cercarial chaetotaxy differs from that of P. phillerouxi. Mollusc host: Isidora guernei belongs to the same genus as Isidora truncata and I. alluaudi, reported hosts to P. microbothrium. Therefore the material is provisionally identified as P. microbothrium. To confirm this, a strain of P. microbothrium from naturally infected Bos taurus in Egypt was studied. Miracidia were used to experimentally infect Isidora truncata; cercariae obtained were identical to those previously described for this species from I. truncata and I. alluaudi. Cercarial chaetotaxy was not significantly different from that of material from North Senegal. They represent therefore two strains of Paramphistomum microbothrium.

Observation of miracidia of twelve species of Schistosoma shows the fundamental epidermal cell pattern is: 6, 9, 4, 3. Comparison of superficial argentophilic organites permits us: --to divide these species into three inequal groups: mansoni group: Schistosoma mansoni, S. rodhaini. haematobium group: S. haematobium, S. bovis, S. indicum , S. intercalatum, S. margrebowiei , S. mattheei, S. nasale and S. spindale . japonicum group: S. japonicum, S. incognitum . --to emphasize the relatively narrow specificity between members of each group and the snail-hosts. --to position the above species of Schistosoma within the Schistosomatoidea . Furthermore this character gives us some idea of the degree of evolution of species of Schistosoma.

Two ophthalmotrichocercous cercariae, very similar as concerns their morphological and anatomical characteristic, parasitize two distinct species of marine Prosobranches: Sphaeronassa mutabilis and Amyclina corniculum. The development of these two cercariae has been followed through the corresponding adult stages. The life cycles of these two lines of Trematodes were shown to be different not only for the first intermediate host but also for the second hosts (Pelecypods); only the final hosts are shared (Sparus auratus, Pagellus erythrinus and P. mormyrus). Additionally the endemiotops (where the life cycle develops) are fundamentally different. Beaches of fine sand with a depth of 0 to 10 m are the endemiotop of the line arising from S. mutabilis whereas hydrodynamically calm muddy biotops (depth between 0 and 10 cm) found at the periphery of prairies of Cymodocea nodosa are the endemiotop of the line arising from A. corniculum. A biometrical study of every larval stage shows significant differences between those two lines. In spite of these differences, the most part of morphological, anatomical and biological characteristics are the same among the various stages of the two lines. So we think the two lines could be, in fact, two populations of the same species, Lepocreadium pegorchis M. Stossich, 1900 which are found together into the definitive hosts, because these fishes are living into the ecosystems characteristic of the two lines. If so, we should be faced to a noteworthly example of ecological vicariance.

Twenty species of the family Helicidae (Gastropoda, Pulmonata) from the N.W. of Spain were tested as hosts for D. dendriticum in experimental conditions. The relationship between the egg hatching in the digestive tract and the development of sporocysts (108-110 days after egg ingestion) was studied. Three species were found to be new intermediate hosts of this trematode: Candidula intersecta , Helicella corderoi and H. jamuzensis . On the basis of the results obtained, the ecological value of the positive species in the life cycle of the parasite is discussed.

Cercariae and metacercariae of Meiogymnophallus strigatus (M. V. Lebour, 1908) have been found in some places along the coast of Camargue (South of France). Sporocysts and cercariae are parasites of Tellina tenuis. Metacercariae occur in various Bivalves, mainly in Donax trunculus and D. semistriatus. Cercariae and metacercariae are described. Relationship between cercariae and metacercariae is demonstrated. Metacercarial microhabitat is delimited. Reaction of D. trunculus in front of the metacercarial infection is studied. Some metacercariae are free-living in the extrapallial space, between the mantle and the shell. These larvae have an advanced genital maturity. Most of the metacercariae are massed together and are enclosed by the host's epithelium. Their excretory vesicle, which is packed with blackish granules, almost fills the entire body. Attempts to infect laboratory reared birds by feeding metacercariae from Donax trunculus were not successful. The natural final host is unknown. In consideration of the metacercarial anatomy, Cercaria strigata M. V. Lebour, 1908 is placed in the genus Meiogymnophallus H. L. Ching, 1965.

The Schistosoma-Mollusc compatibility was tested in two Schistosoma japonicum-Oncomelania hupensis combinations originated from mainland China. The first combination is a combination maintained for more than 30 years in laboratory, the second consisted of a laboratory strain of S. japonicum and a strain of O. h. hupensis taken in the field (Jiangxi province). The fully absence of sporocyst throwing out and hemocyte infiltration 24 h. after transplantation suggest a perfect compatibility of the two combinations. Concerning the test carried out on a natural population of O. h. hupensis, the result obtained might reveal that the schistosomiasis transmission area from Jiangxi province represents focuses with high risk.

Gymnophallus rebecqui n. sp. replace Parvatrema sp. 1 J. Rebecq, 1964. Metacercariae are described. They occur free in the extrapallial space of Cerastoderma glaucum and Abra ovata, at the central part of the valves. Pallial epithelium hypertrophy is induced by metacercariae and damages are produced at the inner face of the shell of Abra ovata. Adults have been reared in laboratory hosts (Aythya ferina, A. fuligula, Anas platyrhynchos, Tadorna tadorna and Larus argentatus michaellis). Natural adults have been discovered in the anterior and median gut of Aythya ferina, A. fuligula and Anas clypeata. Adults are described and compared with other related Gymnophallid species. This new species is not a member of Parvatrema but belongs to Gymnophallus genera.

The authors describe the biological cycle of the Trematoda Dicrocoelium lanceolatum in Lebanon and in Syria: two principal first hosts are the Gastropoda: Theba syriaca and Xerophila vestalis; the second intermediate host is the ant Formica (S.) rufibarbis var. clarorufibarbis very common near fresh water in herbous lands, over 1,000 m of altitude. The last host is the Sheep, the Cow and probably the Goat. A humain case is commented.

Research on the transmission of Hemiurid Trematode Halipegus ovocaudatus in experimental and natural conditions demonstrates the following: --the miracidium grows into a sporocyst producing rediae in the Mollusc Planorbis planorbis; -- the cystophorous cercariae become mesocercariae in the hemocoele of Copepodes or finally Ostracodes when swallowed; -- the mesocercariae become matacercariae in the mesenteron of larval Odonates (Zygoptera and Anisoptera) when these larvae swallow the Crustacea; -- the metacercariae become become adults in the Amphibial Rana ridibundal perezi which feeds on dragonflies. The four hosts (Mollusc -- Crustacean -- Odonat -- Amphibian) are obligatory in the life cycle for it is impossible to infect the Insects directly with the cecariae or the frog (tadpoles as well as adults) with the mesocercariae. The different stages of the life cycle of H. oveocaudatus aredescribed and the mode of the transmission is compared with the other species of Halipegus and with the Trematodes in general. The adaptative value of the lengthening of the cycle is discussed from the point of view of the conquest of terrestrial hosts by the Hemiurid Trematodes.

The life-cycles of Echinostoma revolutum and E. echinatum were carried out by using cercariae emitted by naturally infected Molluscs. E. revolutum strain was issued from Lymnaea auricularia, E. echinatum from Lymnaea truncatula and Planorbis planorbis, Planorbarius corneus produced an Echinostome which may possibly be E. echinatum or another species E. sp. Metacercarial stages and adults were obtained from laboratory experimental hosts. None of these adult Echinostomes displayed well-defined morphological differences: nevertheless their respective larval stages exhibited discrepancies used for species diagnosis. Cercarial chaetotaxy is given for every batch and compared with that of other species described as E. audyi, E. lindoense and E. caproni; discriminating features are discussed.

The release of Schistosoma japonicum cercariae from the People's Republic of China shedded by Oncomelania hupensis was observed hourly under laboratory conditions: LD 9 - 15, T degrees = 25 degrees C. Daily periodicity of emergence was recognized during the light period. Peaks emergence occurs between 2 and 5 p.m. Results are compared with other geographical strains of S. japonicum.

A monthly study of populations of Littorina saxatilis (mollusc, gasteropod) very strongly parasited has allowed to establish relations between the said mollusc and some parasite trematodes which live in it. A selection of animals was done in two stations of the Roscoff region (Finistere). A total of more than 1.000 individuals have been examined in each station. Eleven species of cercairs have been spotted. It has appeared that the Microphallus similis was the most represented: 79,86% of the total. This rate of parasitism does not change much throughout the year. The populations of molluscs strongly parasited by Microphallus similis show an important castration. A double association of cercairs remains rare but is yet possible. It appears that aged individuals are the most parasited. It seems that there would be a growth of parasites more important in females than in males.

32 dairy-goat farms of Touraine were investigated for Muellerius capillaris infection. Faecal and Molluscs samples were collected in Spring and Autumn. The factors of risk for goat were the abundance of Helix aspersa in Spring and of Deroceras reticulatum in Autumn. The infestivity of pasture was related to the infection of goat in Spring but not in Autumn. The faecal larval output in goats depended on the breed of goat at both periods; environmental factors were also of importance.

Study of Senegal cercariae emitted by naturally infected snails or by snails experimentally infected using eggs from human urine or from sheep liver, and study of the corresponding eggs. The relative position of the dorsal sensillae of cercariae is described by an "AD index" and the ratio length/width of eggs by an "L/l index." At the present time, we have not finished the epidemiological studies, certain experiments are imperfect and the isoenzyme analysis of the corresponding adults is incomplete. Nevertheless information given by the indices AD and L/l agree and lead us to admit the existence of a Schistosome different to mattheei, haematobium and bovis and which, following Brumpt and Gretillat we refer to as Schistosoma curassoni. If one relies on the indices, the study indicates that: a) S. mattheei has not been found in Senegal, b) S. bovis is quite rare, c) S. haematobium apparently exists in pure infections in Casamance and in mixed infections with S. curassoni in man in the north and in the east, d) S. curassoni is apparently the dominant species in domestic ruminants and in man in the north and in the east, e) Bulinus umbilicatus is the principal vector of S. curassoni and S. haematobium.

The way of entry and the localization of the larvae of Morerastrongylus andersoni (Petter, 1972), parasite of African Gerbillidae Rodents, were studied in Limnaea stagnalis L. and Planorbarius corneus (L.). The entry occurs by ingestion: indeed, in the Molluscs killed immediatly after one-half to one hour contact with infested Rodents; droppings, the majority of the larvae are found in the digestive tract. After several hours, the larvae are located in the connective tissue and in the muscles and they are distributed everywhere in the Mollusc's body.

This paper deals with life-cycle of Renicola lari J. Timon-David, 1933. Description and illustration are given. Sporocyst development occurs inside the visceral mass of Cerithium mediterraneum and C. Rupestre (Mollusca Prosobranchia). Cercariae are planktonic; they are swallowed up by the second intermediate host, Atherina hepsetus and A. boyeri (Teleostean fishes). Cercariae perforate intestine wall. Metacercariae are encysted in liver. Adult flukes have been recovered in kidneys of uninfected Larus argentatus and L. ridibundus after exerimental contamination with naturally infected fishes. Cercariae of Renicola lari differ from Plagiorchid type cercariae by the following characters : stylet lacking ; very large excretory bladder ; they develop into metacercariae in fishes. Cercariae of R. lari seem to Rhodometope type cercariae ; they have the same excretory bladder. Cercariae of R. lari differ from Rhodometope cercariae in lacking fins on their tail.

In Gymnophallidae life-cycle, the primary host is very often a Lamelli-branch, rarely a Prosobranch; the second intermediate host is usually a Pelecypod, rarely a Prosobranch or an Annelid. The first host is generally sedentary; consequently, cercariae are not widely spread. The second intermediate host cannot explore all the environment. These characters are not in favour of the parasite. Adaptation of Gymnophallid cycle consists in a very large cercarial productivity (several millions for only one first host). The recruiting modalities of Gymnophallid larvae by the second intermediate host are not always the same. Two different mechanisms have been discovered. The first one consists of a limited recruiting. The number of metacercariae is not always growing up during the host-life. This number depends on the volume of microhabitat. The top number is reached when microhabitat is saturated. The second one consists of a illimited recruiting. The number of parasites increases during all the second host life. This peculiarity is possible because the metacercariae are permanently carried out of the microhabitat where they had settled. Parasites are indeed progressively surrounded by pallial proliferations and become enclosed inside pockets of host tissues. Thus, microhabitat is always free of parasites and infection can go on. There must be a correlation between the mechanism of the recruitment of Gymnophallid larvae by a given second host and the characteristics of the environment where the life cycle unfolds. In confined environment (almost closed lagoons, brackish ponds) the number of cercariae is very large and the recruitment observed is limited. Then, the host-life is preserved. In wide open stations, where hydrodynamism is important, cercariae are scattered. The recruitment observed is illimited. This peculiarity is probably an adaptative factor permitting concentration of larvae in the second intermediate host.

Chetotaxy of a cercaria parasite of Cerithium meditteraneum is studied. Sensory receptors C III, St V, St DL, AID, PI and U, are similar to those of Maritrema linguilla and Maritrema subdolum. However in the three cercariae, the ventral, dorsal and lateral papillae, except AID and PI (V, L, D) are different. The chetotaxy of this cercariae shows that they belong to the genus Maritrema. Investigations of the biological cycle are under way to verifie this hypothesis.

The author lists forty eight different species of larval digenean trematodes, observed in 20,000 molluscs belonging to the genus Hydrobia (H. ulvae, H. acuta and H. ventrosa). These hosts were examined from twelve different salt marshes and estuaries around the coasts of France (seven on the Channel, three on the Atlantic Ocean and two on the Mediterranean sea). The collections were made in fifteen sites from 1973 to 1977. The list of the species of larval trematodes found in each site is shown in fifteen tables. These one sum up the prevalence of parasitism in each population of molluscs collected and at times its incidence over a period of two years or more.