Specialized structures on the border between rhizocephalan parasites and their host's nervous system reveal potential sites for host-parasite interactions.

Rhizocephalan barnacles are a unique group of endoparasitic crustaceans. In their extreme adaptation to endoparasitism, rhizocephalan adults have lost almost all features of their free-living relatives but acquired an outstanding degree of control over the body of their hosts (mostly decapods). The subtle influence exercised by rhizocephalans on the physiology, morphology and behaviour of their hosts is a vivid example of the most intimate host-parasite interactions but their mechanisms are very poorly known. In this study we examined the morphology and the adaptive ultrastructure of the organs invading the nervous system of the host in two rhizocephalan species from the families Peltogastridae, (Peltogaster paguri) and Peltogasterellidae (Peltogasterella gracilis). We found two essentially different types of structures involved in interactions of these two rhizocephalans with the nervous system of their hosts: modified rhizocephalan rootlets lying inside the ganglia and the neural fibres of the host enlacing the trophic rootlets of the parasites. We suggest that both these structures may be highly specialized tools allowing the parasite to interact with the host on the humoral level via neuromediators, hormones, attractants and trophic factors.

Parasites in the thoracic ganglion of Pachygrapsus marmoratus (Brachyura: Grapsidae) from the coast of Portugal.

We examined 149 marbled shore crabs, Pachygrapsus marmoratus, from the coast of Portugal for parasites. In particular, we focused our effort on the crab thoracic ganglion. The thoracic ganglion is the largest concentration of nervous tissue in a crab and thus, parasites associated with this organ are well situated to influence host behavior. We found metacercariae of two microphallid trematode species in the thoracic ganglion. We also found a microsporan and an apicomplexan associated with the thoracic ganglion. Other parasites not associated with the thoracic ganglion included gregarine trophozoites which were present in the digestive diverticulae in some of the crabs and the entoniscid isopod, Grapsion cavolini. Metacercariae of one of the trematodes (probably Microphallus pachygrapsi (Deblock and Prevot)), may influence the mortality of its host.

[Karyometric analysis of selected neurohormonal cells of the snail Lymnaea stagnalis (L.) under conditions of natural infection with digenetic trematode parthenites]. / Kariometryczna analiza wybranych komórek ukladu neurohormonalnego slimaka Lymnaea stagnalis (L.) w warunkach naturalnego zarazenia partenitami przywr digenetycznych.

To supply more documentary evidence for the effect of parasitic infection on activity of neurosecretory centres in the cerebral ganglia of the snail host, caudo-dorsal and light green cells of adult individuals of Lymnaea stagnalis naturally infected with digenean parthenites were subjected to karyometric analysis. In infected animals significant enlargement of nuclear volumes of both examined types of neurosecretory cells was ascertained. Mean nuclear volume of the light green cells in snails infected with Furocercariae was significantly lower in comparison with the individuals infected with parthenites from groups Echinostomata and Xiphidiocercariae. In remaining cases differences in nuclear volumes among subpopulations distinguished on the ground of an infection factor were not statistically significant.