Setation and setal groups on antenna 1 of Ridgewayia klausruetzleri, Pleuromamma xiphias, and Pseudocalanus elongatus (Crustacea: Copepoda: Calanoida) during the copepodid phase of their development

Setae added to the antenna 1 of three species of calanoid copepods during copepodid development are allocated to setal groups present on the adult antenna 1. Development of these setal groups is not homogeneous; for a given setal group the copepodid stage at which the first seta appears and at which setal addition is completed varies; whether the setal group is trithek or quadrithek in adult males also varies. These variations suggest several sets of setal groups as candidates for the presumed extra groups added during the adaption of an ancestral calanoid copepod to the pelagic environment. Among these, a set of late developing setal groups is preferred. A model for adding setal groups during copepodid development assumes three source groups are responsible for adding 16 progeny groups.