Definition of species groups of Oncaeidae (Copepoda: Cyclopoida) as basis for a worldwide identification key

Abstract

The copepod family Oncaeidae is widely distributed in the world's oceans and includes many small and abundant species. Due to their small size and the existence of sister and sibling species in different parts of the ocean, species identification is very difficult. Quantitative studies on copepod communities usually consider oncaeids at the family level only, or present uncertain species names, when based on regional identification keys not established for the study area. This paper aims to develop the basis for an improved taxonomic resolution of oncaeids in ecological studies. It summarizes the most relevant morphological elements to characterize the seven presently known genera and to define in addition 16 species groups within the paraphyletic taxon Oncaea s.l. On this basis, a worldwide identification key for oncaeids is presently being developed, restricted to genera and species groups, with species included as far as the state of knowledge allows.

Keywords:

• Copepoda
• Oncaeidae
• morphology
• taxonomy
• identification

Acknowledgements

We wish to thank Dr Y. Nishibe (Biological Oceanography Section, Tohoku National Fisheries Research Institute, Shiogama, Miyagi, Japan) for making available his unpublished data about a new oncaeid species from Japanese coastal waters. Dr H. Itoh (Suidosha Ltd., Kawasaki, Japan) kindly informed one of us (RBS) about the presence of a new species of the vodjanitskii/atlantica-group in the Pacific near Japan. We are indebted to Dr D. McKinnon (Australian Institute of Marine Sciences, Townsville, Australia) for providing specimens of some new morphospecies of Oncaeidae from fine mesh net plankton samples in the eastern Indian Ocean.