• Phylum Mollusca
  • Class Bivalvia
  • Subclass Pteriomorphia
  • Order Arcoida
  • Genus Glycymeris
  • Species Glycymeris nummaria (Linnaeus, 1758)


The Stirone riverbanks (Parma, Italy) host a rich and well preserved invertebrate marine fauna, belonging to the Castell’Arquato Basin formation. These deposits developed from the Late Miocene (Messinian, 6 Ma) to the Pleistocene, after the NW migration of the Po Plain – Adriatic foredeep. The Miocene section is composed of deep-sea sediments, changing to epibathyal and shelf during Pliocene and Pleistocene times, when the regressive trend led to the establishment of continental conditions. In these deposits, very abundant fossil of Glycymeris nummaria have been collected.

Right valve slightly equilateral, with a circular outline; orthogyrate umbo.
Prionodont hinge with “V” shaped serial teeth becoming smaller in the central part. Relatively low and laterally extended ligament area. External duplivincular amphidetic ligament.
The adductor muscle scars are dimyarian anisomyarian; anterior muscle scar is triangularly shaped and slightly bigger than the oval shaped posterior one; integripalliate shell. The marginal area is crenate and the inner shell presents  fine radial striae.
The shell is opaque white. Ornamentation consists of light radial costellae and fine light-beige and purple colored growth lines.

Dimensions: 4.4 cm x 4.3 cm x 1.6 cm.
Age: Gelasian-Calabrian, Pleistocene
Stratigraphic distribution: Early Cretaceous – Recent
Sampling site: Stirone river (Piacenza, Italy)