A new ophiocistioid with soft-tissue preservation from the Silurian Herefordshire Lagerstätte, and the evolution of the holothurian body plan

Rahman, IA, Thompson, JR, Briggs, DEG, Siveter, DJ, Siveter, DJ and Sutton, MD (2019) A new ophiocistioid with soft-tissue preservation from the Silurian Herefordshire Lagerstätte, and the evolution of the holothurian body plan. Proceedings. Biological sciences, 286 (1900). (doi:10.1098/rspb.2018.2792).

Abstract

Reconstructing the evolutionary assembly of animal body plans is challenging when there are large morphological gaps between extant sister taxa,as in the case of echinozoans (echinoids and holothurians). However, theinclusion of extinct taxa can help bridge these gaps. Here we describe anew species of echinozoan, Sollasina cthulhu, from the Silurian HerefordshireLagersta¨tte, UK. Sollasina cthulhu belongs to the ophiocistioids, an extinctgroup that shares characters with both echinoids and holothurians. Usingphysical –optical tomography and computer reconstruction, we visualizethe internal anatomy of S. cthulhu in three dimensions, revealing inner softtissues that we interpret as the ring canal, a key part of the water vascularsystem that was previously unknown in fossil echinozoans. Phylogeneticanalyses strongly suggest that Sollasina and other ophiocistioids representa paraphyletic group of stem holothurians, as previously hypothesized.This allows us to reconstruct the stepwise reduction of the skeleton duringthe assembly of the holothurian body plan, which may have been controlledby changes in the expression of biomineralization genes.

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Contributors

Author: JR Thompson

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