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A Silurian sea spider

Nature volume 431, pages 978980 (21 October 2004) | Download Citation



Pycnogonids (sea spiders) are marine arthropods numbering some 1,160 extant species. They are globally distributed in depths of up to 6,000 metres, and locally abundant1,2; however, their typically delicate form and non-biomineralized cuticle has resulted in an extremely sparse fossil record that is not accepted universally3. There are two opposing views of their phylogenetic position: either within Chelicerata as sister group to the euchelicerates4,5,6,7, or as a sister taxon to all other euarthropods8. The Silurian Herefordshire Konservat-Lagerstätte9 in England ( 425 million years (Myr) bp) yields exceptionally preserved three-dimensional fossils that provide unrivalled insights into the palaeobiology of a variety of invertebrates10,11,12,13,14. The fossils are preserved as calcitic void in-fills in carbonate concretions within a volcaniclastic horizon15, and are reconstructed digitally12. Here we describe a new pycnogonid from this deposit, which is the oldest adult sea spider by 35 Myr and the most completely known fossil species. The large chelate first appendage is consistent with a chelicerate affinity for the pycnogonids. Cladistic analyses place the new species near the base of the pycnogonid crown group, implying that the latter had arisen by the Silurian period.

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This work was supported by the Leverhulme Trust, NERC and English Nature. K. Saunders is thanked for technical assistance; C. Arango, R. Bamber and D. Waloszek for discussion; G. Boxshall, J. Dunlop and D. Waloszek for pre-prints of their papers; S. de Grave for providing Recent material; and R. Fenn, T. Hall and J. Sinclair for general assistance.

Author information


  1. Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3PS, UK

    • Derek J. Siveter
    •  & Mark D. Sutton
  2. Geological Collections, University Museum of Natural History, Oxford OX1 3PW, UK

    • Derek J. Siveter
  3. Department of Geology & Geophysics, Yale University, PO Box 208109, New Haven, Connecticut 06520-8109, USA

    • Derek E. G. Briggs
  4. Department of Geology, University of Leicester, Leicester LE1 7RH, UK

    • David J. Siveter


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Competing interests

The authors declare that they have no competing financial interests.

Corresponding author

Correspondence to Derek J. Siveter.

Supplementary information

Image files

  1. 1.

    Supplementary Figure 1

    Expansion of Figure 2; cladogram of pycnogonids including fossil taxa (see Figure 2 for legend).

Word documents

  1. 1.

    Supplementary Methods

    Details of methodology for cladistic analyses.

  2. 2.

    Supplementary Note 1

    Details of functional argument for interpretation of walking-leg segmentation.

  3. 3.

    Supplementary Note 2

    Details of general functional morphology and mode of life.

Excel files

  1. 1.

    Supplementary Table 1

    Data matrix and character definitions for cladistic analyses.


  1. 1.

    Supplementary Video 1

    Movie comprising serial grinding images from OUM C.29571. Slice interval is 20 µm, field of view horizontally is 5.15 mm.

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