|Tracing the evolution of the holothurian body plan through stem-group fossils|Smith, A.B.; Reich, M. (2013). Tracing the evolution of the holothurian body plan through stem-group fossils. Biol. J. Linn. Soc. 109(3): 670-681. hdl.handle.net/10.1111/bij.12073
In: Biological Journal of the Linnean Society. Academic Press: London; New York. ISSN 0024-4066, more
Devonian; Echinodermata [WoRMS]; Holothuroidea [WoRMS]; Marine
Fossil record; Hunsrück Slate
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The fossil echinoderm Palaeocucumaria, from the early Devonian Hunsrück Slate of southwestern Germany, has been studied using both traditional techniques and X-ray microtomography, and its anatomy clarified. Phylogenetic analysis shows that it is a stem-group holothurian with a combination of characters that help understand how the modern (crown-group) holothurian body plan developed. Echinoids and holothurians have evolved along different paths, by differential growth of the larval- and rudment-derived body regions. Palaeocucumaria shows that late stem-group holothurians had a water vascular organization with a single external madreporite and calcified stone canal leading to the aboral end of the peripharyngeal coelom, and five primary radial water vessels that gave rise to tentacle-like tube-feet. This fossil data, in combination with a molecular phylogeny based on 18?s-like rRNA gene sequence data, is used to order evolutionary steps in the making of the crown-group holothurian body plan.