Kirengellida Explained

The Kirengellids are a group of problematic Cambrian fossil shells of marine organisms. The shells bear a number of paired muscle scars on the inner surface of the valve.

These fossils have conventionally been regarded as monoplacophoran molluscs, and possibly ancestral to gastropods or cephalopods.^[1] They were presumed to be exogastric on the presumption that their larger muscle scars were anterior,^{[2] [3]} but it may be dangerous to compare these scars with molluscan musculature. In any case, they coiled in the opposite direction to Romaniella. However, their calcitic shells, the position of the muscle scars, and putative association with secondary shell elements, make a brachiopod affinity possible, by analogy with the mobergellans: a group of phosphatic shells from the same time period, with a similar set of muscle scars. There is also strong similarity to the contemporary brachiopod group, the Craniopsids. In the case of this diagnosis, a simple lophophore apparatus is postulated to sit between the muscle scars and the edges of the shell.^[4] On the other hand, Vendrasco (2012) reaffirmed the interpretation of the kirengellids as molluscs, noting that the Kirengella muscle scar pattern is also similar to what occurs in monoplacophorans.^{[5] [6]} Bouchet et al. (2017) classified Kirengellida as an order within the subclass Tergomya.^[7]

Included taxa

After ^[4]

• Kirengella Rozov, 1968 (Upper Cambrian)
  • † Kirengella alta Whitfield 1889
  • Kirengella ayaktchica - type species
  • Kirengella expansus
  • † Kirengella kultavasaensis Doguzhaeva 1972
  • Kirengella oregonensis
  • Kirengella pyramidalis
  • † Kirengella rectilateralis Berkey 1898
  • † Kirengella stabilis Berkey 1898
  • Kirengella washingtonense
• Hypseloconus (Upper Cambrian)
• Lenaella (Tremadoc / Lower Ordovician)
• Nyuella (Tremadoc / Lower Ordovician)
• Romaniella (Arenig / late Lower Ordovician)
• Moyerokania (Arenig / late Lower Ordovician)
• Angarella (Arenig / late Lower Ordovician)
• Pygmaeoconus (Llanvirn / early Middle Ordovician)

References

• S. N. Rozov. 1975. A new order of the Monoplacophora. Paleontological Journal 15(1):39-43
• G.P. Wahlman. 1992. Middle and Upper Ordovician symmetrical univalved mollusks (Monoplacophora and Bellerophontina) of the Cincinnati Arch region. United States Geological Survey Professional Paper 1066(O):1-123

Notes and References

1. e.g.
2. Yochelson, E.L.. An alternative approach to the interpretation of the phylogeny of ancient mollusks. Malacologia. 17. 2. 165–191. 1978.
3. Yochelson, E.L. Webers, G.F.. 2006. A restudy of the Late Cambrian Molluscan fauna of Berkey (1898) from Taylors Falls, Minnesota. Minnesota Geological Survey Report of Investigations . 64. 60.
4. BRACHIOPOD IDENTITY OF THE ALLEGED MONOPLACOPHORAN ANCESTORS OF CEPHALOPODS. Dzik, Jerzy. Malacologia . 52 . 1 . 97–113 . 2010.
5. Book: Vendrasco, M. J. . 2012 . Early evolution of molluscs . Averkii Fyodorov . Havrila Yakovlev . Mollusks: Morphology, Behavior and Ecology . https://www.researchgate.net/publication/246548102 . Nova Science Publishers . 1–43 . 9781621009870 .
6. Cope . J. C. W. . Ebbestad . J. O. R. . Tergomyan molluscs from the Early Ordovician of the Llangynog Inlier, South Wales, UK . 2023 . PalZ . 10.1007/s12542-023-00667-5 . free .
7. Bouchet . P. . Rocroi . J.-P. . Hausdorf . B. . Kaim . A. . Kano . Y. . Nützel . A. . Parkhaev . P. . Schrödl . M. . Strong . E.E. . 2017 . Revised classification, nomenclator and typification of gastropod and monoplacophoran families . Malacologia . 61 . 1-2 . 1-526 . 10.4002/040.061.0201 .