Describe the annelid nervous system.

• A. Ventral nerve cord, anterior ganglia (brain)
• B. Dorsal nerve cord
• C. Nervous system absent
• D. Nerve net

Answer: (A)

Annelids have a centralized nervous system with a ventral nerve cord and an anterior brain-like mass of ganglia. A pair of cerebral ganglia at the front acts as a brain, and from there a ventral nerve cord runs the length of the body, with segmental ganglia in each body segment. These segmental ganglia coordinate the muscles and nerves of their segment, forming a ladder-like network that allows coordinated movement along the worm or annelid. This arrangement—ventral nerve cord plus anterior ganglia—is characteristic of annelids.

Dorsal nerve cords are typical of chordates, not annelids; a nerve net is common in simpler organisms like cnidarians; and some animals lack a nervous system, which does not describe annelids.