INTRODUCTION

At this moment the Order Harpacticoida contains about 2757 species in about 346 genera distributed among 33 families. Most species are free-swimming in marine or brackish waters, although a few are ectoparasites of corals, tunicates, crabs and baleen whales. Only three families, 27 genera and about 700 species are found exclusively in freshwaters.

One family, 117 genera and some 1415 species have been described since 1940 and thus do not appear in Lang's monograph (Lang, 1948). Naturally this has rendered obsolete many of his excellent keys, indeed they can now be very misleading to the non-specialist. Most of the new species belong to the marine benthic meiofauna and there is evidence that research on the ecology and physiology of this fauna is being impeded by the difficulty of rapidly identifying the species. In the early 1970's the International Association of Meiobenthologists discussed this problem, which also concerns taxa other than harpacticoids, and taxonomist members were asked to construct keys which would enable non-taxonomists to identify their material with the least expenditure of time and effort.

As keys that enable identification to species by persons unfamiliar with the technicalities of the particular group of animals are very difficult to design it was suggested that an acceptable compromise would be keys to the genus level accompanied by a note of the literature required to take the identification through to species. The keys that follow are designed to that end, although in many cases it proved relatively easy to continue the process to the species level.

Several friends have advised on the format and have helped to remove mistakes from the early drafts, and I am indebted particularly to Bruce Coull and Keith Goodman, but I must remain responsible for any errors that have persisted.