Patterns of setal numbers conserved during early development of swimming legs of Copepoda (Crustacea)

During swimming leg development, the number of setae present on the exopod and endopod of the bilobed bud, the transformed swimming leg with 1-segmented rami and the swimming leg with 2-segmented rami of copepods is analysed. For swimming leg 1, the most frequent number of setae on the presumptive rami of the bilobed bud is found at a higher percentage among copepod species than the most frequent number of setae for either the transformed swimming leg with 1-segmented rami or the swimming leg with 2-segmented rami. However, for swimming legs 2–4 the most frequent number of setae for the the transformed swimming leg with 1-segmented rami is found at a higher percentage of species than that on either the bilobed bud or the swimming leg with 2-segmented rami. Thus, in the cases of swimming legs 2–4, species with different numbers of setae on the presumptive exopod and endopod of the bud bilobed bud develop the same number of setae on the rami of the transformed swimming leg with 1-segmented rami. Increasing the number of species analysed is expected to make more robust the hypothesis that the number of setae on the transformed swimming leg with 1-segmented rami is conserved relative to the number of setae on the bilobed bud.