The Ostracoda are a sub-class of relatively small crustaceans which occur in most aquatic habitats, ranging in size from 0.3 mm interstitial forms to the large (30 mm) oceanic myodocopids of the genus Gigantocypris. Their unique structure is dependant upon the carapace which is in the form of two, hinged, valves enclosing the body. Little can be seen of the complicated feeding, swimming, nervous and reproductive systems operated by these active little animals.
Most aquatic biologists can recognise an ostracod as such but, the editors suspect, comparatively few have managed to identify one to species. Consequently, this numerically important group of Crustacea has been sadly neglected by scientists – but not by many the planktivores which include some ostracods in their diets. Halocyprids are the second-most abundant prey, after copepods, in the stomach contents of some very abundant fishes at mesopelagic depths. Some fish and siphonophore species specialise in ostracod predation.
The main problem for scientists has been the lack of a modern identification guide: a problem that three volumes of Synopses have now rectified for the main groups of these animals in Northem European waters. Synopsis No. 42 covered the freshwater fonns and Synopsis No. 43 the marine and brackish water species of the Superfamilies Cypridaceae and Cytheracea. Publication of the present volume complements these works and extends the coverage offshore.