Despite descending from heavily calcified ancestors, the holothuroid skeleton is fully internal and composed of microscopic ossicles and a ring of plates bound by connective tissue, the calcareous ring. The calcareous ring provides support for the water vascular system, nerve ring, pharynx and tentacles, and is a point for insertion of musculature. Still, it is one of the least studied structures of the holothuroid’s body. Here, we used high-resolution μCT images to describe the anatomy and functional morphology of the calcareous ring macrostructure of eight phylogenetically diverse dendrochirotid species. The structures observed were highly variable at the subfamily level, especially at the point of tissue attachment. To aid future phylogenetic studies, we listed 23 characters and performed a preliminary cladistic analysis. The two topologies obtained support the claims that the simple, cucumariid ring is ancestral to the mosaic-like phyllophorid ring; however, they did not support the monophyly of this cucumariids. They also did not support the family Sclerodactylidae, which was described based on the ring morphology and whose subfamilies are nested within the Phyllophoridae as traditional classifications suggest. Differently from the ossicles, which are highly homoplastic, the general homoplasy index of the calcareous ring characters was relatively low. This result highlights the importance of this structure for phylogenetic inference. Unfortunately, time since collection, rough collection methods and fixation can damage the skeleton, and the calcareous ring is often overlooked in taxonomic descriptions. This is the first broad comparative study of the calcareous ring. We hope that the data presented here will improve our understanding of holothuroid relationships and facilitate studies on holothuroid biology and evolution.