Material and methods
We included a wide array of representative species from all pan- and peracarids in this study (Table 1). Specimens were chosen from the various orders for the diversity of form they display. All specimens came from the crustacean collection of the Zoological Museum, University of Amsterdam.
Initially, camera lucida drawings of the posterior body regions of specimens were made, though only a few are included herein. Subsequently, appropriate specimens were chosen for examination with electron microscopy (species with an asterisk in the appendix) with a JEOL JSM-35C scanning electron microscope.
In addition, we studied 4-d multi-layered photographic sequences of early development in the amphipod Orchestia cavimana showing the process of anus formation.