Kirengellida

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.

Kirengellida Temporal range: Late Cambrian–Mid Ordovician PreꞒ Ꞓ O S D C P T J K Pg N
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Brachiopoda (?)
Order:	†Kirengellida
Family:	†Kirengellidae Rozov 1975

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.^[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]

Included taxa

After ^{[4]: fig. 5}

• 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)