Microconchida

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Microconchida
Temporal range: Upper Ordovician - Middle Jurassic (Taylor and Vinn, 2006)
Palaeoconchus angulatus (Hall, 1861) on a brachiopod from the Middle Devonian (Givetian) of Michigan
Scientific classification
Kingdom: Animalia
Phylum: Mollusca (?)
Class: †Tentaculita
Bouček, 1964
Order: †Microconchida
Weedon 1991
Genera
Helicoconchus elongatus, a microconchid from the Lower Permian of Texas. (See Wilson et al., 2011).
Punctaconchus midfordensis (Richardson, 1907). Bajocian, Clypeus Grit Member, Worgan’s Quarry, Gloucestershire, UK.

The Order Microconchida is a group of small, spirally-coiled, encrusting fossil "worm" tubes found from the Upper Ordovician to the Middle Jurassic (Bathonian) around the world (Weedon, 1991; Vinn, 2006, 2010; Vinn and Mutvei, 2009; Zaton and Vinn, 2011). They have lamellar calcitic shells, usually with pseudopunctae or punctae and a bulb-like origin. Many were long misidentified as the polychaete annelid Spirorbis until studies of shell microstructure and formation showed significant differences (Taylor and Vinn, 2006). All pre-Cretaceous "Spirorbis" fossils are now known to be microconchids (Taylor and Vinn, 2006). Their classification at the phylum level is still debated. Most likely they are some form of lophophorate, a group which includes phoronids, bryozoans and brachiopods. Microconchids are phylogenetically closely related to the other encrusting tentaculitoid tubeworms, such as Anticalyptraea, trypanoporids and cornulitids (Vinn, 2010).

References

  • Taylor, P.D. & Vinn, O. 2006. Convergent morphology in small spiral worm tubes ("Spirorbis") and its palaeoenvironmental implications. Journal of the Geological Society, London 163:225-228.
  • Vinn, O. 2006. Two new microconchid (Tentaculita Bouček 1964) genera from the Early Palaeozoic of Baltoscandia and England. Neues Jahrbuch für Geologie und Paläontologie 2006:89-100.
  • Vinn, O. 2010. Adaptive strategies in the evolution of encrusting tentaculitoid tubeworms. Palaeogeography, Palaeoclimatology, Palaeoecology 292:211–221.
  • Vinn, O. & Mutvei, H. 2009. Calcareous tubeworms of the Phanerozoic. Estonian Journal of Earth Sciences 58:286-296.
  • Weedon, M.J. 1991. Microstructure and affinity of the enigmatic Devonian tubular fossil Trypanopora. Lethaia 24:227-234.
  • Wilson, M.A., Yancey, T.E. and Vinn, O. 2011. A new microconchid tubeworm from the Lower Permian (Artinskian) of central Texas, USA. Acta Palaeontologica Polonica 56:785-791 doi:10.4202/app.2010.0086.
  • Zaton, M., Wilson, M.A. and Vinn, O. 2012. Redescription and neotype designation of the Middle Devonian microconchid (Tentaculita) species ‘Spirorbis’ angulatus Hall, 1861. Journal of Paleontology 86:417-424.
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