Complex sentence: It contains several major orders and suborders: the Arcoida, Ostreoida, Pectinoida, Limoida, Mytiloida, and Pterioida, and it also contains some extinct and probably basal families, such as the Evyanidae, Colpomyidae, Bakevelliidae, Cassianellidae and Lithiotidae.
Split into simpler sentences: It contains several major orders, including the Arcoida, Ostreoida, Pectinoida, Limoida, Mytiloida, and Pterioida. It also contains some extinct and probably basal families, such as the Evyanidae, Colpomyidae, Bakevelliidae, Cassianellidae, and Lithiotidae.