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Differentiating Jingle shells

Valve morphology is highly variable, and an unreliable taxonomic feature.
The genera Anomia, Heteranomia and Pododesmus can be differentiated using gill morphology (Winckworth, 1922) and the number of the muscle scars on the upper valve.

Anomia: “W” shaped gill lamella, 3 muscles scars
Heteranomia: “U” shaped gill lamella, 2 muscle scars – scars smooth.
Pododesmus: “W” shaped gill lamella, 2 muscle scars – scars furrowed.

Species can sometimes be differentiated using the position of the muscle scars, though Holmes (2017) notes that it is not a consistent character in all species.

Holmes (2017) says “Heteranomia is cosmopolitan, monospecific and is represented by only Heteranomia squamula (Linnaeus 1758).” To me, this sounds like a species-complex waiting to be described, almost every “cosmopolitan, monospecific” species turns out to be morphologically similar sibling species. For now, any Jingle shell with a simple “U” shaped gill is Heteranomia squamula.

Examples
Obs shows the three scars of Anomia: https://www.inaturalist.org/observations/11492415
Obs shows 2 scars, no furrows of Heteranomia: this obs
Obs show 2 scars & furrows of Pododesmus: https://www.inaturalist.org/observations/73375218