Final answer:
Annelids and mollusks are major groups of Lophotrochozoa, with mollusks being especially diverse in marine environments. Protostomes, which include Ecdysozoa like arthropods that molt, have their evolutionary relationships redefined thanks to molecular evidence, distinguishing them from Lophotrochozoa.
Step-by-step explanation:
The annelids and mollusks are significant groups within the Lophotrochozoa, showcasing a diverse array of species and biological success, with mollusks representing a considerable portion of marine biodiversity. Protostomes like mollusks, annelids, and arthropods differ developmentally from deuterostomes, as the blastopore in protostomes becomes the mouth during embryonic development. This distinction is crucial for understanding evolutionary relationships. Among Protostomes, the Ecdysozoa, such as arthropods, undergo ecdysis or molting of their exoskeleton, differentiating them from the non-molting Lophotrochozoa. Molecular evidence has redefined the relationships among these invertebrates, placing annelids more closely with mollusks within the Lophotrochozoa and assigning arthropods to the molting Ecdysozoa clade.