Mytella charruana (d’Orbigny, 1846) (= Mytilus falcatus)

Measuring at up to 7.5 cm long, the Mytella charruana is extremely inequilateral, the beaks found right at the anterior end. It is elongate, rounded on both ends, and resembles a half open fan, the anterior end being pointed and the posterior end broad. Its color is purple, blue, or brown, with a prominent olive, black or yellow-brown periostracum, traces of it usually being seen even in worn specimens. The exterior surface is smooth except for irregular growth rings and the margins are uncrenulated. There are two cardinal teeth in each valve, but in the right one the posterior or lower tooth is bifid the lateral teeth are absent. The ligament is external and bordering this ligament is a row of 100 or more minute teeth (but some are often worn away). The interior of the shell is smooth, purple (whitish in worn specimens) and pearly. This species is fairly common.