The ventral nerve cord with fused ganglia is a feature of which phylum?

• A. Arthropods
• B. Echinoderms
• C. Mollusks
• D. Cnidarians

Answer: (A)

Nervous system layout across animal groups helps explain why this feature points to arthropods. In arthropods, the nervous system runs along the ventral side as a nerve cord made of segmental ganglia. In many arthropods these ganglia fuse into a single, continuous chain along the ventral nerve cord, aligning with their segmented bodies and coordinated movement. This fused ventral chain contrasts with echinoderms, which rely on a diffuse nerve net and nerve rings rather than a ventral cord; mollusks, while possessing multiple ganglia and nerve cords, do not exhibit a ventral nerve cord with fused ganglia in the same way; and cnidarians have only a simple nerve net without a central ventral nerve cord.