Changes during early copepodid development of podoplean copepods: common ancestry or convergence

Examples are given of parasitic podopleans that change behaviour, and often morphology, between the first and second copepodid stages. The first copepodid is free-swimming, dispersive and infective; the second copepodid is found attached to or within its host and usually has undergone changes in morphology. Among free-living podopleans, changes in behaviour but not morphology are documented. Strengths and weaknesses of different evolutionary explanations are considered for these changes, including descent from a common free-living ancestor, convergences from several free-living ancestors, or a mixed model. More observations of free-living podopleans, like harpacticoids and cyclopoids, closely associated with the benthos, would be particularly valuable in testing each explanation.