Heterosaccus indicus Boschma parasitises the blue swimming crab Neptunus pelagicus. During January 1967, the authors examined 1836 crabs caught by crab trips in the vicinity of the Regional Centre of Central Marine Fisheries Research Institute, Mandapam Camp. While 12.2 per cent of the total population examined was found to be infested, 28.1 per cent of the females had parasites. The ratio of female hosts to male was 1:1.3.: It was also observed that S .8 per cent of the infested crabs possessed more than one parasite