Final answer:
Acorn worms are similar to earthworms with segmented bodies, while sea angels are planktonic mollusks with wing-like appendages for swimming; they differ significantly in anatomy and lifestyle.
Step-by-step explanation:
The primary difference between acorn worms and sea angels can be found in their respective anatomies and behaviors. Acorn worms, part of the hemichordate family, are more similar to earthworms, with their segmented bodies consisting of many small segments. On the other hand, sea angels are a type of planktonic mollusk with gossamer-like wings used for swimming. The acorn worm is generally found in a benthic habitat, while the sea angel, possessing a more specialized and predatory lifestyle, actively hunts planktonic prey in the open ocean. Both invertebrates represent different ways organisms have adapted to their environments to obtain energy.