Tracing the evolution of the holothurian body plan through stem‐group fossils

摘要: The fossil echinoderm Palaeocucumaria, from the early Devonian Hunsruck Slate of southwestern Germany, has been studied using both traditional techniques and X-ray microtomography, its anatomy clarified. Phylogenetic analysis shows that it is a stem-group holothurian with combination characters help understand how modern (crown-group) body plan developed. Echinoids holothurians have evolved along different paths, by differential growth larval- rudment-derived regions. Palaeocucumaria late had water vascular organization single external madreporite calcified stone canal leading to aboral end peripharyngeal coelom, five primary radial vessels gave rise tentacle-like tube-feet. This data, in molecular phylogeny based on 18 s-like rRNA gene sequence used order evolutionary steps making crown-group plan. © 2013 Linnean Society London, Biological Journal Society, 2013, 109, 670–681.