Stenothecoida

{{Short description|Extinct class of lophotrochozoans}} {{Distinguish|Stenothecidae}} {{Automatic taxobox | fossil_range = Early–mid-Cambrian, {{Fossil range | 525|500|refs=<ref name=K00>{{cite book|title=Molluscs, hyoliths, stenothecoids, and coeloscleritiphorans|chapter-url=https://www.researchgate.net/publication/264808572|doi=10.7312/zhur10612-015|chapter=15. Mollusks, Hyoliths, Stenothecoids, and Coeloscleritophorans|year=2000|last1=Kouchinsky|first1=Artem V.|pages=326–349|isbn=9780231505161}}</ref><ref name=K12>Kouchinsky, A. V., Bengtson, S., Runnegar, B.N., Skovsted, C.B., Steiner, M., and Vendrasco, M.J. (2012). Chronology of early Cambrian biomineralization. Geol. Mag. 149, 221–251.</ref> }} | taxon = Stenothecoida | authority = Yochelson, 1968<ref>{{Cite journal | doi = 10.1111/j.1502-3931.1969.tb01250.x| title = Stenothecoida, A Proposed New Class of Cambrian Mollusca| journal = Lethaia| volume = 2| pages = 49–62| year = 1969| last1 = Yochelson| first1 = Ellis L.| issue = 1| bibcode = 1969Letha...2...49Y}}</ref> | subdivision_ranks = Genera | subdivision = {{Genus list | Stenothecoides |Resser | ''Bagenovia'' |Radugin |Cambridium| Horný, 1957 | Bagenoviella |Aksarina | Sulcocarina |Aksarina |Kaschkadakia |Aksarina |Makarakia |Aksarin }} (given in {{JSTOR|1739764}}) }}

'''Stenothecoida''' is a taxon of bivalved fossils from the Early to middle Cambrian period. They somewhat resemble brachiopods or bivalve molluscs.

==Affinity== Their affinity is uncertain. They were considered by E. L. Yochelson 1968{{citation needed|date=November 2016}} to belong to Mollusca, whereas Runnegar and Pojeta (1974) suggested that they might be 'bivalved monoplacophorans'. This said, the morphology of the shell does not resemble the shell of any other class of molluscs;<ref>{{Cite journal | last = Peel | title = Peel, J.S. 2021, Pseudomyona from the Cambrian of... Bulletin of Geosciences, 96, 195-215| url = http://www.geology.cz/bulletin/contents/art1827| year = 2021}}</ref> they also look a little like brachiopods<ref name=K00/> It's not clear whether their two valves are each other's mirror images, as in bivalve molluscs, though they aren't identical to one another [?].<ref name=K00/> It's more likely that the valves each have a single plane of symmetry (as in brachiopods), suggesting a brachiopod affiliation.<ref name=K00/> There is also evidence for a pedicle, further supporting their brachiopod affinity.<ref name="h982">{{cite journal | last1=Johnston | first1=Paul | last2=Streng | first2=Michael | title=Morphology and relationships of the enigmatic stenothecoid pan-brachiopod Stenothecoides—New data from the middle Cambrian Burgess Shale Formation | journal=Acta Palaeontologica Polonica | volume=66 | date=2021 | doi=10.4202/app.00928.2021 | doi-access=free | url=https://www.app.pan.pl/article/item/article/item/app009282021.html?pdf=39 | access-date=2025-01-17 | page=}}</ref>

As with many other Cambrian taxa,<ref>1. Cohen, B.L., Holmer, L.E., and Lüter, C. (2003). The brachiopod fold: a neglected body plan hypothesis. Palaeontology 46, 59–65.</ref><ref>Skovsted, C.B., Betts, M.J., Topper, T.P., and Brock, G.A. (2015). The early Cambrian tommotiid genus ''Dailyatia'' from South Australia. Mem. Assoc. Australas. Palaeontol. 48, 1–117.</ref> it has been suggested that they arise through reduction of a ''Halkieria''-like ancestor.<ref name=K00/>

== Mineralogy== Thought to be low-Mg calcite.<ref>Kouchinsky, A. V. et al. Chronology of early Cambrian biomineralization. Geol. Mag. 149, 221–251 (2012).</ref>

==Occurrence== The earliest occurrence dates to 525 Ma.<ref name=K12 />

These fossil shells have been found in Canada, China, Greenland, Kazakhstan, Kyrgyzstan, and the USA.

==References== {{Reflist}} * [http://www.springerreference.com/docs/html/chapterdbid/43567.html Start of article at Springer Reference] * [https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=65472 Paleobiology Database info on this class] * [http://onlinelibrary.wiley.com/doi/10.1111/j.1502-3931.1969.tb01250.x/abstract Abstract of a Yochelson 2007 article on the proposed class]

Category:Prehistoric mollusc taxonomy Category:Mollusc classes Category:Prehistoric protostome classes