Based on a comparison of the internal musculature of the fifth and sixth limbs of the cypridinid ostracode Isocypridina quatuorsetae, it is tentatively concluded that the sixth limbs of members of the Cypridinidae are biramous, each bearing an exopod represented by a cluster of small bristles (setae) and an endopod with two podomeres. The protopod contains a coxa with two endites and a basis with one endite.