| Kirengellida Temporal range: | |
|---|---|
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Monoplacophora |
| Subclass: | Tergomya |
| Order: | † Kirengellida Rozov, 1975 |
| Superfamilies [1] | |
| Synonyms [1] | |
Romaniellida | |
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. [2] They were presumed to be exogastric on the presumption that their larger muscle scars were anterior, [3] [4] but it may be dangerous to compare these scars with molluscan musculature. [5] In any case, they coiled in the opposite direction to Romaniella . [5] 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. [5] 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. [5] 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. [6] [7] Bouchet et al. (2017) classified Kirengellida as an order within the subclass Tergomya. [8]
