ACARTIA BIFILOSA (COPEPODA, CALANOIDA) - A CLARIFICATION OF THE SPECIES AND ITS VARIETIES INERMIS AND INTERMEDIA

Adults of the calanoid copepod Acartia bifilosa and the varieties iner mis and intermedia are examined and described. This study brings to li ght discrepancies in the available keys to all these forms. Individual s previously reported and also deposited in museum collections as A.bi filosa var. inermis and var. intermedia are shown to be similar to A.b ifilosa with respect to characteristics previously used for classifica tion. Acartia bifilosa and its varieties were shown to possess setules on the dorsal side of female and male urosomes, although there was gr eat variation in the size and position of these. The fifth legs (P5) o f adult males and females were very similar in all individuals examine d, regardless of how they were previously classified, although the ori ginal descriptions are generally inadequate or misleading. These resul ts bring into doubt the arguments used by Rose (1929) to report A. bif ilosa var. inermis. A single unified species, A.bifilosa (Giesbrecht), is suggested here, with some of the variation in its form being detai led. We believe errors may have occurred because of the angle from whi ch features were previously examined, and because some of the features could be missed using light microscopy.