Abstract
The siphonostome copepod Ophiopsyllus found on the brittlestar Ophiocomella ophiactoides at Discovery Bay, Jamaica damages the host in such a way as strongly to suggest that it is feeding on the surface tissues. This supposition is supported by the structure of the mouth parts. Although reported from another brittlestar elsewhere, O. reductus is apparently specific to O. ophiactoides at Jamaica. We present details of the distribution of the copepod on the host, preliminary information on the prevalence and intensity of the infestation and data on reproductive capacity of the copepod. The micro-anatomy of the animal is considered with respect to attachment and movement as well as feeding. Data apparently showing a relationship between presence of the copepod and decreased tendency of the host to undergo cross-disc division are also presented.