Nectonema munidaeBrinkmann (Nematomorpha) parasitizingMunida tenuimanaG.O. Sars (Crust. Dec.) with notes on host-parasite relations and new host species

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Abstract
A survey of the genus Nectonema is given and an estimation of available facts seems to indicate that the genus comprises 3 or perhaps 4 species. An investigation of the breeding in M. Tenuimana showed that the onset of sexual maturity occurred at 12.5 mm Cpl, but berried females did not outnumber unberried ones until at 15.5 mm Cpl. The breeding period comprised 10 months, and only during the 2 “embryo-free” months did the females moult. Juvenile specimens of M. tenuimana were much more heavily infested by N. munidae than adults, and the frequency of the parasite was considerably greater in specimens which simultaneously were infested by the epicaridan parasite Pseudione crenulata. Single infestations by N. munidae were equally distributed in both sexes of the host, while multiple infestations by N. munidae and simultaneous infestations by N. munidae and P. crenulata were much more abundant in female hosts. The size of the parasite was not correlated with the size of the host, unless the latter was very small, and the size of the individual parasites was not affected by the presence of other parasites in multiple infestations. No effects caused by the parasite upon the growth, moulting, breeding or normal activities of the host could be detected. The life-cycles of the parasite and the host are discussed, and it is concluded that there is no clearly restricted spawning period for N. munidae. Further, M. tenuimana was generally infested when young, but infestations also occurred in very old hosts. The copulation of N. munidae was studied and internal fertilization was established. Some laboratory experiments indicated that adult males are capable of finding their way to adult females, but not to juveniles. N. munidae was also recorded from Pagurus pubescens and from the new host species Munida sarsi and Pagurus cuanensis. A study of this material definitely contradicted the earlier reported rigid host specificity of N. munidae. A survey of the different records of Nectonema with regard to host species is given.