Here we report on our initial successes in overcoming both of these technical challenges. We have developed a technique for injecting reagents into live S. purpuratus larvae, specifically targeting the echinus rudiment: a series of tissues that develop within the larval body, and are fated to form predominantly the oral structures of the urchin juvenile. By injecting rhodaminated dextran, we were able to consistently label structures within the rudiment, providing a technique for visualizing these structures in live larvae. Furthermore, we have manipulated the normal ontogeny of juvenile structures by injecting Vivo-Morpholinos –a class of morpholino oligonucleotides that are designed to cross cell membranes– into various compartments within the rudiment of late stage purple urchin larvae. Specifically, we document an inhibition in growth and elongation of incipient adult spines using vMOs directed against p16 and p58b, two genes known to be involved in skeletal elongation in urchin embryos. We are confident in the specificity of the phenotypes that we report for the vMO rudiment injections for the following reasons: 1) we did not observe CUDC-907 side effects skeletogenic phenotypes in controls, and specifically using the control vMO, in either soaked embryos or injected larvae; 2) we were able to provide evidence that p58b vMOs are effectively eliminating the correct splice variant of the gene and consequently lead to a functional knockdown; 3) the phenotypes that we did observe in embryos with our p16 and p58b vMOs phenocopy previously published results obtained with standard MOs injected into eggs ; and 4) the phenotypes that we observed in our rudiment injections indicated that injected rudiments continued to develop normally after injection, across all treatments – it was only a subset of the skeletal elements specifically in the p16 and p58b vMO treatments that showed inhibited growth. Therefore, our results indicate, for the first time, that morphogenesis of the juvenile sea urchin can be manipulated by morpholino injection. As a corollary, we provide evidence that p16 and p58b are required for normal skeletal elongation during sea urchin juvenile skeletal development, as they are during embryogenesis, a finding consistent with the expression of much of the purple urchin larval skeletogenic regulatory network in juvenile rudiments. The basic protocol that we described should be feasible for most inverted microscopes and injection configurations. One of the most significant challenges that we faced was ascertaining the exact location of the tip of the needle relative to the many tissue layers within the echinus rudiment. The injection microscope we used was not equipped with epi-fluorescence; having that capability would have been preferable, as it would have allowed us to confirm injection location without the need to mount the post-injection larvae under raised cover glass. With our setup, we had the best success when viewing the needle with a partially-closed diaphragm under 2002400x magnification. Watching the liquid being expelled from the needle tip also gave hints as to the location of the injection.