1. 1. The integrative nature of the parasite host association was discussed, specifically with regard to the metabolic effects of parasitization as well as the physiological manifestation of infection in relation to the host's nutritional physiology. Endocrine interactions were also considered. 2. 2. Relationships involving parasitic insects, including members of the orders Diptera, Hymenoptera and Strepsiptera, parasitic helminths, including members of the phyla Acanthocephala and Nematoda and the classes Cestoidea and Trematoda of the Platyhelminthes, as well as parasitic crustaceans in association with their invertebrate and/or vertebrate, intermediate, paratenic as well as definitive hosts were considered. 3. 3. A broad conceptual or “topic” approach to understanding symbiotic relationships was emphasized. De-emphasis of descriptive categorization and the use of benefit/harm as criteria characterizing parasitic relationships was suggested. 4. 4. The hypothetical concept of host regulation was briefly examined and the use of anthropometric descriptors such as “beneficial” and “harmonious” in parasitology discussed.

Biochemical and physiological effects of metazoan endoparasites on their host species.

Five hydrolytic enzymes (acid phosphatase, aryl sulphatase, β-glucuronidase, N-acetyl-β-glucosaminidase, and non-specific esterase) have been studied histochemically in the cells of the digestive gland of Mytilus edulis, Helix aspersa, and certain other lamellibranchs and gastropods. All the enzymes studied have basically similar distributions.



In the digestive cells, the enzymes occur in cytoplasmic granules which are believed to be primary lysosomes; in vacuoles which contain phagocytosed food material; and in vacuoles containing lipofuscin granules, which are the residues of digestive activity.



In the basiphil cells of M. edulis, most of the enzymes are localized in a few cytoplasmic granules; non-specific esterase, however, is found throughout the cytoplasm. In the calcium cells of H. aspersa and the other pulmonate gastropods studied, the enzymes are either in cytoplasmic granules, or distributed diffusely throughout the cytoplasm. Acid phosphatase is also found in the calcium spherules, especially in H. aspersa.



In the excretory cells of H. aspersa and the other pulmonates studied, the enzymes are found in granules in the cytoplasm, and in the lipofuscin granules which lie in the vacuoles of these cells.

The distribution of some hydrolytic enzymes in the cells of the digestive gland of certain lamellibranchs and gastropods

The evolution of altruism does not necessarily require an extreme amount of kinship. This point is illustrated with an analysis of altruistic behavior in the Trematode parasite Dicrocoelium dendriticum, which apparently can evolve even when the parasites of the host are derived from as many as five different parents.

How nepotistic is the brain worm

Histochemical studies of the digestive gland of Lymnaea truncatula have revealed features of the normal digestive processes in which at least 3 cell types are involved: digestive cells, mucus cells and basiphil cells. An intracellular vacuolar digestive system containing lysosomal enzymes appears to operate in the digestive cells. Parasitization by Fasciola hepatica evokes considerable structural and histochemical changes in the host digestive gland. There is, in general, increased cellular vacuolation together with increased lysosomal enzyme activity. The overall effect appears to be an increase in intracellular digestive processes, including autolysis, and it is suggested that this may be a consequence of the host attempting to maintain its nutritional requirements under parasitic stress. Starvation of un-infected specimens induces structural and histochemical changes which closely resemble the effects of parasitization.

Histochemical changes in the digestive gland of Lymnaea truncatula infected with Fasciola hepatica.

A systematic review of the parasites, pathogens and commensals of the edible cockle (Cerastoderma edule) and of the lagoon cockle (Cerastoderma glaucum) has been completed. A total of 59 different conditions have been reported throughout the range of both of these hosts; of these 50 have been reported in edible cockles, and 28 in lagoon cockles. Cockles are hosts to viruses, bacteria, fungi (including Microsporidia), Apicomplexa, Amoeba, Ciliophora, Perkinsozoa, Haplosporidia, Cercozoa, Turbellaria, Digenea, Cestoda, Nematoda, Crustacea and Nemertea. A number of these have been reported sporadically although they may be associated with mortalities. In particular, mortalities have been associated predominately with digeneans and some protistan infections. In many cases pathology is marked in affected animals and parasites have been shown to reduce fecundity, alter burrowing behaviour and limit growth. This review provides information on the individual and population effects of these conditions as well as providing suggestions for future research. In particular, there has been a lack of taxonomic rigour applied to many studies and as a result there are a number of erroneous host records. There is a need to re-describe a number of parasite species and to determine the life cycle of those considered to be important mortality drivers.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0025315412000537

A review of the infectious agents, parasites, pathogens and commensals of European cockles ( Cerastoderma edule and C. glaucum )

The effects of parasitism by the daughter sporocyst of Cercaría bucephalopsis haimaena Lacaze-Duthiers, 1854, on the digestive tubules of the cockle, Cardium edule L.

E. A. Bowers

Papers

The effects of parasitism by the daughter sporocyst of Cercaría bucephalopsis haimaena Lacaze-Duthiers, 1854, on the digestive tubules of the cockle, Cardium edule L.