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 orderMicroconchida is a group of small, spirally-coiled, encrusting fossil "worm" tubes from the class Tentaculita found from the Upper Ordovician to the Middle Jurassic (Bathonian) around the world.[1][2][3][4][5] 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.[6] All pre-Cretaceous "Spirorbis" fossils are now known to be microconchids.[6] 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 may be closely related to the other encrusting tentaculitoid tubeworms, such as Anticalyptraea, trypanoporids and cornulitids.[3] Their habitat is more controversial. While there is a consensus that they were present in the seas and in brackish water, there is a debate about their presence in freshwater. Some studies suggested that they colonised freshwater in the Early Devonian,[7][8] whereas others suggest that microconchids never colonised that environment.[9][10] A recent review of the associated fauna failed to find reliable occurrences of microconchids in the Middle Devonian to Early Permian time interval because microconchids seem to co-occur with other signs of marine influence,[11] such as xiphosurans and chondrichthyan egg capsules.[12]
^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.
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 doi:10.1666/11-115.1.
