What did Castracollis look like ?
deutsche Version
Since the formation of the Rhynie chert was facilitated by flooding with silica-enriched water, it was no big surprise when a water-dwelling creature was found among terrestrial vegetation [1].  One can only wonder why it took more than 70 years to discover other crustaceans in the chert [2,3]. (See also
Rhynie Chert News 12. )  
One of the recently discovered species, Castracollis [2] (which is the Latin equivalent of Castlehill, a farm near Rhynie), has been regarded as "one of the most important recent discoveries that bear on the elucidation of branchiopod evolution" [4].
Its tentative reconstruction in [2] involving a hypothetical carapace (shield) is based on only one lump of chert, hence any new finds deserve attention since they may show other details.
A piece of chert found in 2003 revealed several specimens of Castracollis on the surface and on cut faces, among them the one seen below as a cross-section of the anterior part of the body. As a conspicuous feature, what seems to be the carapace is divided into two bulging halves, which does not fit to the reconstruction proposed in [2], see Fig.3.
This lack of compatibility is presently being considered by D. Waloszek at Ulm University. Eventually the present find will lead to a slightly modified reconstruction of this lately discovered crustacean.
Castracollis, cross-section of the anterior part of the body with shieldCastracolis cross-section, contours outlined
Figs.1,2: Castracollis

cross-section of the anterior part of the body
with bulging halves of a divided carapace,
width 3.2mm, contours outlined.

Reconstruction of Castracollis after FAYERS and TREWIN

     Fig.3: Reconstruction of Castracollis wilsonae in [2]
     with hypothetical carapace based on inconclusive
     fossil evidence.
 H.-J. Weiss     2008,   updated 2011

[1]  D.J. Scourfield: On a new type of crustacean ... Lepidocaris rhyniensis ...
     Phil. Trans. Roy. Soc. London (Series B), 214(1926), 153-187.
[2]  S.R. Fayers, N.H. Trewin: A new crustacean from the Early Devonian Rhynie Chert ...
     Trans.Roy. Soc. Edinburgh, Earth Sci. 93(2003), 355-382.
[3]  L. Anderson, W.R.B. Crighton, H. Hass: A new univalve crustacean from the Early Devonian Rhynie chert hot-spring complex,
     Trans.Roy. Soc. Edinburgh, Earth Sci. 94(2004 for 2003), 355-369.
[4]  J. Olesen: Monophyly and phylogeny of branchiopoda, with focus on morphology and homologies of branchiopod phyllopodous limbs,
     J. Crustacean Biol. 27(2007), 165-183.
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