The ontogeny of the musculature and segments of the antennule of Heterocypris incongruens (Ramdohr, 1808) is documented. The musculature of the antennule of the juveniles indicates that during ontogeny the additional segments originate by existing segments dividing. Previously presented hypotheses are tested with these new data. Smith & Martens' (2000) hypothesis on the development of the antennule of Eucypris virens (Jurine, 1820) is supported and is expanded to cover other groups. There are five segments in the early juveniles of most species and some of these divide to form new segments during ontogeny. Additionally, some segments fuse together, and some segments divide and then fuse together again. Most divisions of segments produce two true segments, rather than annulations or secondary joints, but one species shows evidence of an annulation in the antennule.