This Integrative and Comparative Biology scholarly paper (11-page PDF) presents a sophisticated method of microscopy, 4D microscopy (3D time-lapse microscopy), which records the entire development of an embryo and allows detailed analyses of events such as cleavage, cell migration, cell death (apoptosis), and cell differentiation during development. Using tardigrade development as an example, this paper demonstrates that the use of 4D microscopy can reveal new characters and corroborate or disapprove old characters. It also discusses results in the light of recent phylogenetic hypotheses regarding the Arthropoda and their probable sister group, the Cycloneuralia, which together form the Ecdysozoa.
