Deuterostomes comprise three phyla with radically different body plans. Phylogenetic bracketing of the living deuterostome clades suggests the latest common ancestor of echinoderms, hemichordates and chordates was a bilaterally symmetrical worm with pharyngeal openings, with these characters lost in echinoderms. Early fossil echinoderms with pharyngeal openings have been described, but their interpretation is highly controversial. Here, we critically evaluate the evidence for pharyngeal structures (gill bars) in the extinct stylophoran echinoderms Lagynocystis pyramidalis and Jaekelocarpus oklahomensis using virtual models based on high-resolution X-ray tomography scans of three-dimensionally preserved fossil specimens. Multivariate analyses of the size, spacing and arrangement of the internal bars in these fossils indicate they are substantially more similar to gill bars in modern enteropneust hemichordates and cephalochordates than to other internal bar-like structures in fossil blastozoan echinoderms. The close similarity between the internal bars of the stylophorans L. pyramidalis and J. oklahomensis and the gill bars of extant chordates and hemichordates is strong evidence for their homology. Differences between these internal bars and bar-like elements of the respiratory systems in blastozoans suggest these structures might have arisen through parallel evolution across deuterostomes, perhaps underpinned by a common developmental genetic mechanism.

Brooding of young is a reproductive strategy observed in many extant echinoderms, but the evolutionary history of this behaviour is largely unknown due to the scarcity of examples preserved in the fossil record. Here, synchrotron x‐ray tomography is used to describe an exceptionally preserved specimen of the Devonian blastoid echinoderm Hyperoblastus reimanni. The coelomic cavity appears completely preserved in a coiled arrangement partially enclosing organs associated with the digestive, haemal and axial systems. The vault region of the coelom surrounds four structures interpreted as three internally brooded larvae and a gonad. The presence of putative larvae brooded internally in this specimen sheds new light on the reproductive strategies used by blastoids, suggesting they were sexually dimorphic and that internal brooding was acquired early in the group's history. The acquisition of brooding may have been linked to high clastic sediment influx associated with the Appalachian Orogeny, which would have been detrimental to the survival of larvae living at the soupy sediment–water interface.