Gyaltsenglossus senis: A Hemichordate from the Middle Cambrian Burgess Shale.
[sciencythoughts.blogspot.com]
Hemichordate relationships remain contentious due to conflicting molecular results and the high degree of morphological disparity between the two Hemichordate classes, Enteropneusta and Pterobranchia. Additionally, Hemichordates have a poor fossil record outside of the Cambrian, with the exception of the collagenous tubes of the Pterobranchs (which include Graptolites). By the Middle Cambrian, tube-dwelling colonial Pterobranchs and tube-dwelling enteropneusts coexisted, supporting the origin of the Hemichordate body plan earlier in the Cambrian without clarifying the morphology of their last common ancestor.