The peracarid crustacean orders Mysida, Lophogastrida and Stygiomysida were formerly grouped under the name "Mysidacea". Although the treatment in three separate orders is now accepted, we have chosen to present mysids, lophogastrids and stygiomysids in the same web interface. The higher classification (orders, families, subfamilies) follows Meland & Willassen (2007), and the fossil order of Pygocephalomorpha is also included in the database.