Final answer:
Acorn worms have a relatively simple nervous system without a true brain or ganglia. They have nerve cords and a nerve ring around the mouth region that acts as the head ganglion. Nerve cells are organized in a scattered network throughout their body, forming a nerve plexus.
Step-by-step explanation:
In acorn worms, the nervous system is relatively simple and lacks a true brain or large ganglia. They have a nerve cord that runs along their body, with a nerve ring around the mouth region that acts as the head ganglion. The nerve cells are organized in a network scattered across the body, forming a nerve net called a nerve plexus. The signaling molecules in acorn worms' nervous systems are primarily peptides, which perform both excitatory and inhibitory functions.