Final answer:
The trunk of an acorn worm is divided into three regions - the proboscis, collar, and worm-like trunk, differing from the segmented bodies of annelids like earthworms.
Step-by-step explanation:
The trunk of an acorn worm is not specifically addressed in the provided information, which primarily discusses segmented worms and other related invertebrates from the phylum Annelida and Arthropoda. However, the trunk of an acorn worm, which is part of the Hemichordata phylum, is typically divided into three regions: the proboscis, collar, and a long, worm-like trunk. Acorn worms have a different body plan compared to segmented worms like earthworms, which have a body composed of repeating segments that increase flexibility and allow a wider range of motion. Annelids, another term for segmented worms, encompass a variety of species, including earthworms, that display this segmented body structure and often have more developed organ systems than other types of worms.