The Kirengellids are a group of problematic Cambrian
fossilshells 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
monoplacophoranmolluscs, 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.[4] In any case, they coiled in the opposite direction to Romaniella.[4] 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.[4] 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]
^e.g. Yochelson, E. L.; Flower, R. H.; Webers, G. F. (1973), "The bearing of the new Late Cambrian monoplacophoran genus Knightoconus upon the origin of the Cephalopoda", Lethaia, 6 (3): 275–309,
doi:
10.1111/j.1502-3931.1973.tb01199.x
^Vendrasco, M. J. (2012).
"Early evolution of molluscs". In Averkii Fyodorov; Havrila Yakovlev (eds.). Mollusks: Morphology, Behavior and Ecology. Nova Science Publishers. pp. 1–43.
ISBN9781621009870.
^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.
doi:
10.4002/040.061.0201.
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