The advent of urchin genomics has heralded renewed interest in urchin development, and paired with modern manipulation techniques such as morpholino microinjection, the sea urchin is now one of only a handful of animals whose embryos are readily amenable to both classical and contemporary embryological techniques, including blastomere separations, cell transplantation, and more recently, genetic manipulations. While remarkable progress has been made in understanding the molecular and cellular basis of development in sea urchin embryos, comparatively little is known about the development of the adult body plan as the planktonic larva transitions to the benthic juvenile. That is, the range of experimental approaches enjoyed by urchin embryologists has not been applied to the development of juvenile tissues. Complex life histories –development through feeding planktonic larvae and metamorphosis to benthic juveniles– are widespread in the ocean, with numerous hypothesized independent origins of complex from simpler ancestral life cycles. Even more numerous are losses of larval feeding and/or planktonic development hypothesized for many metamorphic phyla. Thus, despite the importance and commonality of complex life cycles in marine organisms, we have little understanding of the internal and environmental factors that regulate the progression of such life cycles in even a single marine species. Sea urchins display one of the most dramatic metamorphic transitions among the animals. Their larvae are bilaterally symmetric, but their juveniles begin development as an asymmetric invagination of larval epithelial cells, which then, in concert with coelomic tissues VE-821 undergo morphogenesis into a juvenile rudiment, all internal to the larval epithelium. During juvenile rudiment development, the pentameral symmetry of the adult forms along with the primordia of many juvenile structures. After larvae having well-developed juvenile rudiments settle to the sea floor and select an appropriate benthic substrate, they rapidly undergo the most dramatic stage of the metamorphic transformation: in a matter of minutes the juvenile everts out of the larval body, the larval ectoderm I s withdrawn, and the juvenile begins to move along the sea floor using its tube feet. While this life cycle transformation in sea urchins has fascinated biologists for centuries, detailed functional studies of late larval development and the metamorphic transition have been lacking, due in large part to lengthy larval periods and the inherent limitations of accessing densely packed forming juvenile tissue. Still, indirectly developing sea urchin larvae are an ideal organism with which to gain insight into juvenile morphogenesis and metamorphosis. With proper technique, large numbers of sea urchin larvae can be reared synchronously to metamorphic competence, detailed descriptions of metamorphic stages have been published and many transient knockdown techniques have been applied to sea urchin embryos. Yet one significant challenge remains: how does one experimentally manipulate the development of juvenile tissues in sea urchins?