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An acercostracan marrellomorph (Euarthropoda) from the Lower Ordovician of Morocco

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Abstract

Enosiaspis hrungnir gen. et sp. nov., a new species of marrellomorph arthropod from the Lower Ordovician (Tremadocian) Fezouata biota of Morocco, is described. This taxon is characterised by the possession of a cordiform dorsal carapace with an anterior notch and a doublure-like structure formed from fused marginal spines, covering the entire body. The head comprises at least five segments which bear an anterior pair of antenna, followed by three pairs of potentially biramous, geniculate appendages. The trunk possesses around 25 pairs of delicate, almost filamentous appendages, which decrease in size posteriorly. Similar features are also found in Xylokorys chledophilia from the Silurian of England, and Vachonisia rogeri from the Devonian of Germany, indicating acercostracan affinities for E. hrungnir. This was tested using a phylogenetic analysis which resolved this taxon as sister taxon to a group composed of the formerly mentioned taxa. The similarities between the ventral spinose carapace doublure of E. hrungnir and the mediolateral spines of marrellid marrellomorphs further support claims that the dorsal shield of acercostracans evolved from the fusion of spinose anlagen, akin to the formation of the carapace of crustaceans.

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Acknowledgments

This work was made possible through the extensive help and support of Peter Van Roy (Yale University, New Haven). Thanks are also due to Susan Butts and Jessica Utrup (both Yale Peabody Museum) for access to specimens in their care, and for providing loans of specimens. Work on the material described in this paper was made possible by NSF Grant EAR-1053247.

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  1. Oxford University Museum of Natural History, Parks Road, Oxford, OX1 3PW, UK

    David A. Legg

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  1. David A. Legg
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Correspondence to David A. Legg.

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Communicated by: Sven Thatje

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Legg, D.A. An acercostracan marrellomorph (Euarthropoda) from the Lower Ordovician of Morocco. Sci Nat 103, 21 (2016). https://doi.org/10.1007/s00114-016-1352-5

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