Development of leg 5 of copepods belonging to the calanoid superfamily Centropagoidea (Crustacea)

Leg 5 development is described for 10 species from 10 genera in 6 families of centropagoidean calanoid copepods. Segment homologies are inferred from the order in which arthrodial membranes, setae, and attenuations are added to ramal segments during late copepodid development. Among centropagoidean males, the grasping chela on the side opposite the male genital pore develops in three different ways. The fixed part of the chela may be a ventral attenuation of the basis, or of the proximal exopodal segment, or of the middle exopodal segment, suggesting that a male leg 5 chela is not a synapomorphy of the Centropagoidea because nonhomologous segments make up the convergent morphology. In like manner, a grasping subchela on the side opposite the male genital pore is expressed in three different ways: basis plus proximal, middle and distal exopodal segments; basis plus proximal and distal exopodal segments; or basis plus distal exopodal segment; so nonhomologous segments also result in a convergent subchela morphology. On leg 5 of adult females, a ventral attenuation of the middle exopodal segment, initially formed at copepodid stage V, is present on species of Centropagidae and Diaptomidae. A ventral attenuation of the exopod initially expressed at copepodid stage V on females of Temoridae is considered a homologous structure, although failure to express the proximal arthrodial membrane of the exopod complicates the interpretation of its origin. A ventral attenuation first appears on the exopod of Pontellidae and Acartiidae at copepodid stage V, but its homologies with the above families are more difficult to determine because neither proximal or distal arthrodial membranes nor setae are present on the adult exopod. The species of Tortanidae studied here does not express a ventral attenuation on the exopod at copepodid stage V or at the adult stage, but adults of some other species of Tortanus do. The ventral attenuation of the exopod of adult female leg 5, initially present at copepodid stage V, is a more likely synapomorphy for the superfamily although evidence for this homologous structure may be difficult to identify due to the secondary loss of setae and arthrodial membranes on the exopod of some species. Presence at copepodid stage V of the presumptive genital somite complex of the adult female is expressed among all centropagoideans studied here and appears to be an unambiguous synapomorphy for species of the superfamily.