Abstract
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.
Highlights
Rhizocephalan barnacles are a unique group of endoparasitic crustaceans
Rhizocephalans are considered as parasitic castrators suppressing the reproductive system of the host[6,32] but in contrast to some other parasitic castrators such as trematodes, which destroy the gonads of the host, rhizocephalan barnacles suppress gametogenesis
We examined the morphology and adaptive ultrastructure of the organs invading the nervous system of the host in two rhizocephalan species, Peltogaster paguri from the family Peltogastridae and Peltogasterella gracilis from new established family Peltogasterellidae[43]
Summary
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). Rhizocephala, or rhizocephalan barnacles, are a group of parasitic crustaceans that have lost almost all morphological characteristics of their free-living relatives due to adaptation to an endoparasitic lifestyle These animals have a modified life cycle[1,2,3,4] and a unique ontogeny resulting in a heavily transformed adult living as an endoparasite within other crustaceans, mostly decapods. Rhizocephalan barnacles show the highest level of integration with their hosts among metazoan parasites[23] and the closest host-parasite interactions They influence the moulting cycle, general physiology, morphology and behaviour of their hosts[6,23,24,25,26,27,28,29,30]. The voracity of the infected individuals increases[39]
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