Abstract
A new species of the cyclopoid copepod genus Hemicyclops, H.xiamenensis, is described from plankton sampled at the mouth of the Jiulong River, southern China. This is the second species of the genus occurring in Chinese waters. The new species is readily distinguishable from its congeners by a combination of features of the fourth pediger, female genital double-somite, caudal ramus, and appendages. Because adults of Hemicyclops are ordinarily associated with benthic animals, the planktonic occurrence of the new species may be interpreted as either, 1) a new mode of life involving diel migration, 2) host switching between day and night, or 3) accidental occurrence.
