The orthothecids are one of the two hyolith orders.[2]
| Orthothecida Temporal range:
| |
|---|---|
Scientific classification 
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Brachiopoda |
| Class: | †Hyolitha |
| Order: | †Orthothecida Marek, 1966 |
| Families | |
| |
Marek diagnoses the order thus: Conchs with a flat or concave ventral surface — opercula with large, flat cardinal processes but without clavicles – tightly sigmoidal, sediment-filled intestine – helens absent.
Sometimes the Circothecidae and Tetrathecidae are split out into a separate order 'Circothecida', which is defined by the bottom surface not being flat, the cardinal processes being pronounced, and a circular rim sometimes showing hints of differentiation into clavicles.[3]
Internal taxonomy
editMarek [3] gives the following diagnoses:
- Orthothecidae: Flat or concave bottom surface of conical shell. Transverse aperture.
Kouchinsky[4] lists the following taxonomic criteria:
- Circothecidae: circular cross-section; same shape and sculpture on upper and lower surfaces.
- Turcurthecidae: oval or lenticular cross-section; top and bottom identical
- Allathecidae: top side flat or slightly convex; bottom side convex
Elsewhere[5]: 243 is stated:
- Tetrathecidae: polyhedral cross-section; shell axially twisted
- Novitatidae: bottom side concave
- Lenatheca: aperture heart-shaped.
Additional genera are not assigned to a family:
References
edit- ^ Malinky, J. M. (2009). "Permian Hyolithida from Australia: The Last of the Hyoliths?". Journal of Paleontology. 83: 147–152. doi:10.1666/08-094R.1. S2CID 85924056.
- ^ Malinky, J.M.; Skovsted, C.B (2004). "Hyoliths and small shelly fossils from the Lower Cambrian of North−East Greenland". Acta Palaeontologica Polonica. 49 (4): 551–578.
- ^ a b "Machaeridians, Chitons, and Conchiferan Molluscs of the Mojcza limestone" (PDF). Archived from the original (PDF) on 2017-10-12.
- ^ Kouchinsky, A. V. (2000). "Skeletal microstructures of hyoliths from the Early Cambrian of Siberia". Alcheringa. 24 (2): 65–81. doi:10.1080/03115510008619525. S2CID 140660142.
- ^ Lipps, Jere H; Signor, Philip W (2013-11-21). Origin and Early Evolution of the Metazoa. ISBN 9781489924278.
- ^ Valent, M. (2012). "Two new orthothecids from the Cambrian of the Barrandian area (Hyolitha, Skryje-Týřovice Basin, Czech Republic)". Bulletin of Geosciences. 87 (2): 241–248. doi:10.3140/bull.geosci.1142.
- ^ Sun, Haijing; Smith, Martin R.; Zeng, Han; Zhao, Fangchen; Li, Guoxiang; Zhu, Maoyan (2018). "Hyoliths with pedicles illuminate the origin of the brachiopod body plan". Proceedings of the Royal Society B: Biological Sciences. 285 (1887): 20181780. doi:10.1098/rspb.2018.1780. PMC 6170810. PMID 30257914.
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