This chapter summarizes important morphological features of trematodes belonging to the family Auridistomidae, with key descriptions relevant to the diagnosis of specific genera within the family.

Abstract This book chapter describes members of the family Leyogonimidae, which are known parasites of the intestine, mesenteries and hepatic system of birds and mammals. A key to genera of the family Leyogonimidae is also provided.

Abstract The Exotidendriidae family includes intestinal and renal parasites of reptiles in Africa, southern Asia and Australia. This chapter describes the taxonomic history and diagnostic characteristics of the family, followed by a key to genera, diagnostic characteristics of each genus, and illustrations of the type species.

The Gyrabascidae family includes parasites of bats and rodents. This chapter describes the taxonomic history and diagnostic characteristics of the family, followed by a key to genera, diagnostic characteristics of each genus, and illustrations of the type species.

Abstract The Urotrematidae family mostly includes parasites of insectivorous bats and occasionally reported from some rodents, lizards and freshwater fishes. This chapter describes the taxonomic history and diagnostic characteristics of the family, followed by a key to genera, diagnostic characteristics of each genus, and illustrations of several type species.

This chapter presents the morphological characteristics of the members of the Family Pleurogenidae. Members of this family are parasitic to amphibians, reptiles, fishes and mammals. A key to the genera is provided. Illustrations of different species belonging to this family are also included.

There are 2 elements that make ‘‘crowding’’ interesting— mechanism (causality) and manifestation (effect). In our companion paper, Larry Roberts addresses mechanisms. Here, we focus on manifestation. As ecologists, it is difficult to get too excited about Clark Read’s paper on the ‘‘crowding effect’’ in cestodes, at least initially. The paper acknowledges clearly that the phenomenon has been observed repeatedly, is mostly a discussion of appropriate techniques, and concludes with a brief overture to causality. Recalling a popular television commercial from several years ago, ‘‘Where’s the beef?’’ The answer lies in the implication of crowding. Simply stated, crowding means too many of something. In the case of worms in the gut of a host, it is obvious that there exists a finite number of individuals that can physically fit into a gut. Crowding is a common phenomenon, certainly not restricted to tapeworms in the small intestine of a rat. It is very, very common in managed systems where the intent is to get the ‘‘biggest bang for the buck.’’ For example, gardeners know that too many plants in a prescribed area will result in a poor crop; so too do aquaculturists raising fishes, crustaceans, or shellfish. Under such artificial conditions, the remedy for alleviating crowding is simple, at least in theory. Either reduce (thin) the target population or artificially enhance the environment. The latter may be accomplished by supplemental feeding, removing toxic wastes, and so forth. Trivial observations perhaps but ‘‘crowding’’ is overwhelmingly common, at least where humans have intervened. But, what of the ecology of crowding in a natural context? We consider crowding as being important ecologically in 2 contexts—first as it relates to predator–prey relationships and second as it relates to the much-maligned idea of competition. In a food web, crowding will always impact most severely on the prey population. If there are too many predators, e.g., the predators are crowded, more prey will be taken simply because there are more things to eat them. Similarly, if there are too many prey, predators will find and, perhaps, capture them more easily. However, our focus here is not on predator–prey relationships, rather it is on crowding as it might relate to parasites in a host. At the time Clark Read’s paper was published, ecology was more qualitative natural history than the quantitative science we know today. If predator–prey interactions could not account for the observed patterns on the distribution and abundance of organisms, then surely the answer must lie in competition. It is perhaps for that reason, that competition was apparently so pervasive that Read ignored manifestation in his paper. Why emphasize what was so readily obvious? Basically, competition takes 2 forms: interference and exploitation. With interference competition, organisms may impact on others in a direct fashion, for example, releasing toxins.

We consider 27 population and community terms used frequently by parasitologists when describing the ecology of parasites. We provide suggestions for various terms in an attempt to foster consistent use and to make terms used in parasite ecology easier to interpret for those who study free-living organisms. We suggest strongly that authors, whether they agree or disagree with us, provide complete and unambiguous definitions for all parameters of their studies.

Populations and therefore communities of intestinal helminths of vertebrates are fueled by recruitment of new individuals from outside the host. The source of new individuals is often an intermediate host that harbors several infective propagules of 1 or more species. Hence these source communities are transmitted in packets of infective propagules to target communities in definitive hosts. Packets not only provide recruits to target communities, but, because a packet of propagules possesses its own structure, it may also transmit structure to the target community. We use this system to examine the contribution that structure in the source pool of propagules makes to the structure of recruitment-driven target populations and communities. By treating the dynamics of such target populations and communities as immigration-death processes, we conclude: (1) Unlike a birth-driven population a recruitment-driven target population will grow to an asymptotic limit even in the absence of density-dependent processes or reaching carrying capacity; (2) the frequency distribution of the number of recruits entering target populations will determine the frequency distribution of adults in target populations; (3) interspecific associations among species in the source community will be transmitted to target communities, but the magnitude of the transmitted associations will depend upon the relative survival rates of the species; and (4) for associations of equal magnitude in a source community, the magnitude of a transferred negative association will be less than the magnitude of a positive association in a target community. Two examples of source communities in salt marsh crabs reveal that source infracommunities exist with the hypothesized structure. Further, the source helminth communities display a greater number of positive than negative interspecific associations. The inequity in transfer and the existence of a greater proportion of positive associations in source communities may explain the widespread occurrence of excess positive associations that has been noted in recruitment-driven communities.

ABSTRACr: Populations and therefore communities of intestinal helminths of vertebrates are fueled by recruitment of new individuals from outside the host. The source of new individuals is often an intermediate host that harbors several infective propagules of I or more species. Hence these source communities are transmitted in packets of infective propagules to target communities in definitive hosts. Packets not only provide recruits to target communities, but, because a packet of propagules possesses its own structure, it may also transmit structure to the target community. We use this system to examine the contribution that structure in the source pool of propagules makes to the structure of recruitment-driven target populations and communities. By treating the dynamics of such target populations and communities as immigration-death processes, we conclude: (1) Unlike a birth-driven population a recruitment-driven target population will grow to an asymptotic limit even in the absence of densitydependent processes or reaching carrying capacity; (2) the frequency distribution of the number of recruits entering target populations will determine the frequency distribution of adults in target populations; (3) interspecific associations among species in the source community will be transmitted to target communities, but the magnitude of the transmitted associations will depend upon the relative survival rates of the species; and (4) for associations of equal magnitude in a source community, the magnitude of a transferred negative association will be less than the magnitude of a positive association in a target community. Two examples of source communities in salt marsh crabs reveal that source infracommunities exist with the hypothesized structure. Further, the source helminth communities display a greater number of positive than negative interspecific associations. The inequity in transfer and the existence of a greater proportion of positive associations in source communities may explain the widespread occurrence of excess positive associations that has been noted in recruitment-driven communities.

The null hypothesis that the number of positive pairwise covariances should equal the number of negative pairwise covariances in samples from communities of randomly associated helminth species was reevaluated. The proportion of positive covariances in a sample from a community of independent species depends upon the proportion of rare species (prevalence less than 10%), the proportion of common species (prevalence greater than 90%), and the size of the sample of hosts. If rare species dominate, then there will be an excess of negative associations; if common species dominate there will be an excess of positive associations. Many helminth communities have more rare than common species, therefore samples from communities that show an equal number of positive and negative covariances have a greater number of positive associations than is expected for randomly associated species. Increased sample size will reduce the sampling bias, but at least 100 hosts are necessary and often 500-7,500 hosts are required. The excess of positive covariances between helminth species in 10 populations of bats disappeared after restricting the analyses to hosts in which both members of a species pair were present. This result suggests that excess positive associations between helminth species in bats are due to joint presences and absences in hosts rather than to interspecific facilitation. Interspecific facilitation would be supported by observed positive correlations between the intensities of individuals of the species pairs.

Twelve populations of bats were examined to determine the extent of interspecific associations in determining the species richness of intestinal helminth infracommunities. The pool of helminth species which was available to individual bats ranged from 2 to 21. The ‘summed binomial’ distribution was determined to underlie the host frequency distribution of the number of helminth species per host. Overall covariation in occurrences of species in replicated communities can be detected by testing for the equality of the observed variance of the host frequency distribution to the variance expected when species are allocated to hosts at random. Where statistically significant the covariance was indicative of a majority of positive rather than negative interspecific associations. As the mean number of species per host in a host population increases not only does the number of positive associations increase but so does the proportion of species pairs which exhibit positive associations. Although there is an increase in the proportion of species pairs which exhibit positive associations as the number of species increases, the magnitude of the associations (as indicated by the mean positive or the mean negative pairwise covariances) does not. Therefore, we concluded that positive interactions are more common than negative interactions in determining the species richness of helminth infracommunities of bats. Further, positive associations become even more important as the community becomes more complex. However, the increased importance is derived from the number rather than the strength of the associations.

Twenty-one species of helminths were recovered from Eptesicus fuscus in Eau Claire, Wisconsin, and thirteen species were collected from E. fuscus in St. Peter, Minnesota. Contingency table analyses of all species pairs from each locality detected no interactions in the St. Peter group. In the Eau Claire group the trematode pairs Paralecithodendrium naviculum – Acanthatrium oligacanthum and Allassogonoporus marginalis – Ochoterenatrema diminutum exhibited positive associations, whereas P. naviculum was negatively associated with the cestode Hymenolepis roudabushi. When the intestinal distribution of each species was summed over all hosts from each locality, the intestinal overlap of each species pair averaged 31% in bats from Eau Claire and 24% in bats from St. Peter. The overlaps dropped to 2% in bats from Eau Claire and 1% in those from St. Peter when intestinal distributions were not summed across hosts. A randomization analysis of intestinal distributions for all pairs of species from the two localities revealed that H. roudabushi overlapped less than expected with P. naviculum in Eau Claire and with the trematode Plagiorchis vespertilionis in St. Peter. The intestinal distributions of four pairs of species from St. Peter and eight pairs from Eau Claire overlapped more than expected. We conclude that contemporary interactions are of minor importance in structuring infracommunities for the two localities and that positive interactions are more common than negative interactions.

The nude (congenitally athymic) mouse, C3H/HeN is highly susceptible to infection with Brugia pahangi (Nematoda: Filarioidea). Normal, hairy mice show a strong thymus-dependent resistance and usually terminate the infection in the larval stages. The present study examined chronological histopathologic changes in the lumbar lymph nodes and adjacent lymphatic vessels of both hosts. In thymic mice, lymphangitis and perilymphangitis reached a maximum 14 to 17 days PI, about the time of disappearance of live worms. The infiltrate showed characteristics of both acute and chronic inflammation: eosinophils, neutrophils, eosinophilic precipitates, and sometimes necrotizing lymphangitis, as well as macrophages and plasma cells. The cellular infiltrate in nude mice was weaker and developed more slowly. Inflammatory responses to identifiable dead worms were seen in both types of hosts but appeared more frequently in thymic mice. Although variable in both models, the granulomas of thymic mice generally showed more tendency to cavitation, greater macrophage or epithelioid cell infiltration, more granulocytes, and appeared to be more destructive than the foreign body responses of nude mice. Whereas lymphangiectasis was generally progressive in nude mice, it was arrested before the end of the third week in thymic mice. In thymic mice, at maximum lumbar lymph node size (17 days), there were large areas of lymphocyte hyperplasia and heavy infiltration of plasma cells. Most nodes returned to normal mean size by the end of the second month. Little or no reactivity was seen in athymic mouse nodes. Our results suggest that some lesions of lymphatic filariasis are potentially thymus-independent: lymphatic fibrosis, lymphangiectasis, accumulations of macrophages and giant cells around disintegrating worms, calcification of worms, intralymphatic thrombosis, and moderate vascular infiltrates including eosinophils.

Cette espece parasite la tortue Chelydra serpentina son hote intermediaire est le gasteropode hydrobiide Amnicola peracuta

trapped in a hilly area close to the town of Sanare (9?45'N, 69?36'W, and 1,250 m altitude). The rodent carcass was brought to the parasitology lab for identification of some whitish bags attached to the rabbit pericardium. Two cysts were removed, with diameters of 2.8 cm and 2.2 cm, respectively. Hydatid fluid was extracted using a syringe. The fluid was observed microscopically, and a high number of protoscolices were seen (Fig. 1). Case two: A second rabbit was trapped in a dry low land, close to San Francisco village (10?17'N, 70?19'W, and 460 m altitude), Torres County, Lara State, and a few hydatid cysts found adhering to the left kidney and the thigh musculature. These cysts were only 1.5 to 2.0 cm in diameter; protoscolices were also removed from the hydatid fluid. In order to identify the larval stages, the brood capsules (n = 20), the protoscolices (n = 70), and the rostellar large hooks (n = 100) were measured; the results are presented in Am. Brood capsules had a thin membrane and measured 515-540 Am (mean: 526). Fully developed protoscolices were 120-157 long by 90-122 in diameter (mean: 136 by 108), and the large rostellar hooks ranged between 31.3-34.8 (mean: 32.6). On the basis of a comparison of the present data with the data published by Rausch et al. apped in a hilly area close t the town of Sanare (loc. cit.), we conclude that these cysts belong to the larval stage of E. oligarthrus. It should be pointed out that after carrying out a survey of over 4,000 mammals in Colombia, D'Alessandro et al., 1981 (loc. cit.) found no lagomorpha (Sylvilagusfloridanus) infected with Echinococcus cysts. Furthermore, we found no prior reference of rabbits involved in the life cycle of E. oligarthrus, and E. vogeli in Venezuela. Consequently, wild rabbits may be included as an alternate intermediate host for E. oligarthrus, at least in this Westcentral region of Venezuela, where pacas and agouti are rarely seen. One of us (MSY) has necropsied 12 pacas in the last 3 years with negative results for E. oligarthrus cysts. Finally, it should be recalled that in the taxonomy of cestode, the morphological characters are not now final criteria for differentiating species, and as stated by other authors (Smyth, 1979. In British Society for Parasitology Symposia, A. E. R. Taylor and R. Muller (eds.). Blackwell, Oxford, Vol. 17, pp. 75-101; Thompson and Kumaratilake, 1982, Trans. Roy. Soc. trop. Med. Hyg. 76: 13-16), other methods like ecological and immunological differences, in vitro cultivation, and protein separative techniques should be used for the identification of cestodes such as Echinococcus and other helminths.

Cette espece parasite les ecrevisses Cambaerellus shufeldtii, C. puer et Procambarus clarkii, les xiphidiocercaires se developpent chez Amnicola peracuta (Mollisca)