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Lace CrabKingdom: Animalia
Sub Period: None
International Age: Emsian (early)
Hunsrück Slate Group
Collector: T. Bastelberger
Acquired by: Field Collection
Width: 5 cm
heap pile "Grube Herrenberg"
This arthropod is a Marrellomorph, a clade of strange looking stem-group arthropods known from the Cambrian Burgess Shale and the slightly older Kaili Fauna in China (Marella), the Silurian Herefordshire Lagerstätte in England (Xylokorys), the Ordovician Basal Upper Fezouata Formation (lower Arenig, or lower Floian), north of Zagora in southeastern Morocco and the Caradoc (Upper Ordovician) in Bohemia (Furca) and the Devonian Bundenbach Shale in Germany (Mimetaster and Vachonisia).
Marrellomorphs lacked mineralized hard parts, so are only known from areas of exceptional preservation, limiting their fossil distribution.
The head shield has two pairs of long rearward directed spikes. Marrellomorphs possessed two pairs of antennae, one long and sweeping, the second shorter and stouter. The two dozen segments each have a pair of six segmented leg / feathery gill structures. There is a tiny, button like telson at the end of the thorax. The best modern guest is that Marrellomorphs are moderately evolved primitive arthropods descended from a common ancestor of the major later arthropod groups.
Reconstruction of Mimetaster hexagonalis
Reconstruction of another Marrellomorph - Marrella splendens - from the Cambrian Burgess Shale in Canada.
A thorough re-investigation of Marrella splendens based on over 1000 specimens was recently published by D. García-Bellido and D. Collins: “A new study of Marrella splendens (Arthropoda, Marrellomorpha) from the Middle Cambrian Burgess Shale, British Columbia, Canada” in Can. J. Earth Sci. 43(6): 721–742 (2006).
The overall form of Mimetaster and other Marrellomorphs suggests that it was a soft-bottom dweller. The wide carapace border would have prevented sinking into unconsolidated sediment.
Mimetaster hexagonalis is the most abundant non-trilobite arthropod from this Lagerstätte. They are considered to live in groups of several individuals; two, three or even more species on one slab are not uncommon. A thorough reinvestigation of Mimetaster based on 123 specimens was recently published by G. Kühl and J. Rust in Paläontologische Zeitschrift, volume 84, number 3, 397-411.
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