Poliometra prolixa is a common species of comatulid crinoid in the Arctic deep sea. In this study, we characterize the ontogenetic development through the cystidean and pentacrinoid stages, using specimens from the LTER (Long-Term Ecological Research) observatory HAUSGARTEN in Fram Strait, Arctic Ocean. While embryos and early larval stages (e.g., the doliolaria) were not observed, adult P. prolixa were observed on a moored experimental platform at 2500 m water depth, suggesting that P. prolixa larvae do not disperse far from their mothers; doliolaria may have an abbreviated pelagic duration period or may be brooded in this species. The cystidean has a short, translucent stalk with a star-shaped attachment disc and a diamond-shaped translucent head. Metamorphosis from the cystidean to the pentacrinoid is characterized by the formation of brachial ossicles from oral ossicles and by fusion of the basal and radial ossicles to form the calyx. The pentacrinoid stalk is more opaque and develops synarthrial joints first at the distal end. Late pentacrinoids have a xenomorphic stalk, bifurcated arms with pinnules, and cirri. We discuss the niche of Poliometra prolixa and also consider the question of whether cystidean and pentacrinoid stages of comatulid crinoids should be considered larval forms.