Mid 19th century; earliest use found in The Penny Cyclopaedia. From scientific Latin Mytilacea (H. M. D. de Blainville Man. de Malacologie et Conchyliologie 531; from Mytilus + -acea, after French Mytilacés (Cuvier, 1817), Mytilacées (Lamarck, 1819)) + -an.