Final answer:
Phoronids from the clade Lophotrochozoa have three body wall layers: ectoderm, mesoderm, and endoderm, making them triploblastic organisms with a more complex structure when compared to diploblastic cnidarians.
Step-by-step explanation:
Phoronids, which belong to the clade Lophotrochozoa, are triploblastic and, therefore, have three body wall layers. The three layers are the ectoderm, mesoderm, and endoderm. These layers are more complex than those in cnidarians, which are diploblastic and only have an ectoderm and endoderm, and unlike the simplicity found in cnidarian digestion and body plan, phoronids show a higher level of organization.
In contrast to the cnidarians' two layers around a digesting cavity, the mesoderm in triploblastic animals like phoronids gives rise to many of the internal structures and organs, adding to their complexity. Therefore, phoronids, like other members of the Lophotrochozoa, exhibit more advanced body plans and organ systems due to this additional germ layer.