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. 2017 Dec;13(12):20170635.
doi: 10.1098/rsbl.2017.0635.

Water vascular system architecture in an Ordovician ophiuroid

Elizabeth G Clark  1 , Bhart-Anjan S Bhullar  2   3 , Simon A F Darroch  4 , Derek E G Briggs  2   3
Affiliations

Water vascular system architecture in an Ordovician ophiuroid

Elizabeth G Clark et al. Biol Lett. 2017 Dec.

Abstract

Understanding the water vascular system (WVS) in early fossil echinoderms is critical to elucidating the evolution of this system in extant forms. Here we present the first report of the internal morphology of the water vascular system of a stem ophiuroid. The radial canals are internal to the arm, but protected dorsally by a plate separate to the ambulacrals. The canals zig-zag with no evidence of constrictions, corresponding to sphincters, which control pairs of tube feet in extant ophiuroids. The morphology suggests that the unpaired tube feet must have operated individually, and relied on the elasticity of the radial canals, lateral valves and tube foot musculature alone for extension and retraction. This arrangement differs radically from that in extant ophiuroids, revealing a previously unknown Palaeozoic configuration.

Keywords: Ophiuroidea; exceptional preservation; water vascular system.

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Conflict of interest statement

We have no competing interests.

Figures

Figure 1.
Figure 1.
Ophioderma sp., histological slides. (a) Cross-section (YPM IZ 077065) and (b) longitudinal section (YPM IZ 077064) of arm stained with haematoxylin (Delafield's) and eosin (prepared by the Yale Osborn Zoological Laboratory in 1943).
Figure 2.
Figure 2.
Protasterina flexuosa (CMC 25001), micro-CT scans. (a) 3D render ventral view of scan A of P. flexuosa (CMC 25001) at 50.24 greyscale value (top), 80% transparency (middle), and 100% transparency (bottom). Greyscale values represent a measure of relative density used in VG Studio MAX. Extracted volume of WVS tissue shown in blue. Radial canals of arms I and V only visible in higher resolution scans. Arms numbered as in [13]. (b) Coronal (purple box) and longitudinal (green box) sections from scan A. Extracted WVS tissue volume shown in blue. The area within the purple box shows higher density WVS tissue pyritization than that in the green box. Arrows indicate examples of where the pyrite has cracked. (c) Enlarged views of arm IV WVS tissue from scan A. (d) Stereo images of Maya model of articulated skeleton and WVS. WVS (blue), ossicle A (green), structure B (purple) [261.35 greyscale value], and lateral (red) [411.35 greyscale value] extracted from scan B; ambulacral (grey) extracted from scan C [600.06 greyscale value].
See this image and copyright information in PMC

References

    1. Zamora S, Rahman IA. 2015. Deciphering the early evolution of echinoderms with Cambrian fossils. Palaeontology 57, 1105–1119. (10.1111/pala.12138) - DOI
    1. Sprinkle J, Wilbur BC. 2005. Deconstructing helicoplacoids: reinterpreting the most enigmatic Cambrian echinoderm. Geol. J. 40, 281–293. (10.1002/gj.1015) - DOI
    1. Dean JD. 1999. What makes an ophiuroid? A morphological study of the problematic Ordovician stelleroid Stenaster and the palaeobiology of the earliest asteroids and ophiuroids. Zool. J. Linn. Soc. 126, 225–250. (10.1111/j.1096-3642.1999.tb00154.x) - DOI
    1. Miller SA, Dyer CB. 1878. Contributions to palaeontology. J. Cincinnati Soc. Nat. Hist. 1, 24–39.
    1. Hunter AW, Rushton AWA, Stone P. 2016. Comments on the ophiuroid family Protasteridae and description of a new genus from the Lower Devonian of the Fox Bay Formation, Falkland Islands. Alcheringa 40, 429–442. (10.1080/03115518.2016.1218246) - DOI