Cassianellidae

The cassianellids are noted for being restricted to the Triassic only, going extinct during the end Triassic extinction event. They are thought to have a close relationship to the longer lived family Bakevelliidae and it is possible the cassianellids may have even evolved from one of the early Triassic bakevelliid genera.^[2] As is found in the Bakevelliidae genus Kobayashites and the Isognomonidae genus Lithiotis, cassianellids are distinguished by the presence of a larval septum which is retained in the adult shell morphology.^[2] Also notable for the entire family is the presence of a primitive alivincular type ligament, termed an alivincular-areate ligament. This form of ligament was widely found in many of the Triassic bivalve families but evolution of more refined ligament systems resulted in the shift away from the alivincular-areate system. Only a few modern families, such as Gryphaeidae, still retain the alivincular-areate ligament system.^[3] Several of the genera, such as Cassianella, have a widespread distribution.^[1] In contrast, Lilangina is known only from Asia, and Septihoernesia from the middle Triassic of northern Italy.^[1]

Cassianellidae Ichikawa, 1958

• Genus Burckhardtia Frech, 1907
• Genus Cassianella Beyrich, 1862 (synonyms = Acinophorus Meek, 1864, Gryphorhynchus Meek, 1864)
• Genus Hoernesiella Gugenberger, 1934
• Genus Lilangina Diener, 1906
• Genus Reubenia Cox, 1924
• Genus Septihoernesia Cox, 1964