microconchida

{{Short description|Extinct order of molluscs}}

{{Automatic taxobox

| taxon = Microconchida

| fossil_range = {{fossil range|Upper Ordovician|Bathonian|Upper Ordovician - Middle Jurassic |refs=(Taylor and Vinn, 2006)}}

| image = MicroconchidDevonianPotterFarm082111.jpg

| image_caption = Palaeoconchus angulatus (Hall, 1861) on a brachiopod from the Middle Devonian (Givetian) of Michigan

| authority = Weedon 1991

| subdivision_ranks = Genera

| subdivision =

• Microconchus
• Palaeoconchus
• Annuliconchus
• Punctaconchus
• Polonoconchus
• Helicoconchus

}}

Image:Helicoconchus elongatus.jpg

Image:Punctaconchus.jpg

{{Portal|Paleontology}}

The order Microconchida 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. 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. All pre-Cretaceous "Spirorbis" fossils are now known to be microconchids. 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. 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,{{cite journal |last1=Zatoń |first1=Michał |last2=Vinn |first2=Olev |last3=Tomescu |first3=Alexandru M. F. |title=Invasion of freshwater and variable marginal marine habitats by microconchid tubeworms – an evolutionary perspective |journal=Geobios |date=1 November 2012 |volume=45 |issue=6 |pages=603–610 |doi=10.1016/j.geobios.2011.12.003 |url=https://doi.org/10.1016/j.geobios.2011.12.003 |issn=0016-6995|url-access=subscription }}{{cite journal |last1=Zatoń |first1=Michał |last2=Wilson |first2=Mark A. |last3=Vinn |first3=Olev |title=Comment on the paper of Gierlowski-Kordesch and Cassle “The ‘Spirorbis’ problem revisited: Sedimentology and biology of microconchids in marine–nonmarine transitions” [Earth-Science Reviews, 148 (2015): 209–227] |journal=Earth-Science Reviews |date=1 January 2016 |volume=152 |pages=198–200 |doi=10.1016/j.earscirev.2015.11.012 |url=https://doi.org/10.1016/j.earscirev.2015.11.012 |issn=0012-8252|url-access=subscription }} whereas others suggest that microconchids never colonised that environment.{{cite journal |last1=Gierlowski-Kordesch |first1=Elizabeth H. |last2=Cassle |first2=Christopher F. |title=The ‘Spirorbis’ problem revisited: Sedimentology and biology of microconchids in marine-nonmarine transitions |journal=Earth-Science Reviews |date=1 September 2015 |volume=148 |pages=209–227 |doi=10.1016/j.earscirev.2015.04.010 |url=https://doi.org/10.1016/j.earscirev.2015.04.010 |issn=0012-8252|url-access=subscription }}{{cite journal |last1=Gierlowski-Kordesch |first1=Elizabeth H. |last2=Falcon-Lang |first2=Howard J. |last3=Cassle |first3=Christopher F. |title=Reply to comment on the paper of Gierlowski-Kordesch and Cassle “The ‘Spirorbis’ problem revisited: Sedimentology and biology of microconchids in marine–nonmarine transitions” |journal=Earth-Science Reviews |date=1 January 2016 |volume=152 |pages=201–204 |doi=10.1016/j.earscirev.2015.11.011 |url=http://dx.doi.org/10.1016/j.earscirev.2015.11.011 |issn=0012-8252|url-access=subscription }} 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,{{Cite journal |last=Laurin |first=Michel |date=30 December 2024 |title=Habitat of early stegocephalians (Chordata, Vertebrata, Sarcopterygii): a little saltier than most paleontologists like? |url=https://doi.org/10.3897/fr.27.123291 |journal=Fossil Record |volume=27 |issue=3 |pages=299–332 |doi=10.3897/fr.27.123291 |issn=2193-0074 |doi-access=free}} such as xiphosurans and chondrichthyan egg capsules.{{cite journal |last1=Lomax |first1=Dean R. |last2=Robinson |first2=Peter |last3=Cleal |first3=Christopher J. |last4=Bowden |first4=Alistair |last5=Larkin |first5=Nigel R. |title=Exceptional preservation of Upper Carboniferous (lower Westphalian) fossils from Edlington, Doncaster, South Yorkshire, UK |journal=Geological Journal |date=2016 |volume=51 |issue=1 |pages=42–50 |doi=10.1002/gj.2602 |url=https://doi.org/10.1002/gj.2602 |language=en |issn=1099-1034}}