A mollusk having tentacles attached to its head.

A mollusk having tentacles attached to its head.

• A. Gastropod
• B. Bivalve
• C. Tentacle
• D. Cephalopod

Answer: (D)

This question tests recognizing which mollusk group has limbs that originate directly from the head. Cephalopods are defined by having their tentacles and arms attached to the head region, forming a head-foot body plan. This arrangement—tentacles emerging from the head—fits octopuses, squids, and their relatives, and is a hallmark of cephalopods. Bivalves, like clams and oysters, lack a distinct head and do not possess these head-attached tentacles. Gastropods, such as snails and slugs, do have a head with sensory tentacles, but their body plan centers on a prominent foot and often a shell, not a cluster of limbs arising from the head. The term tentacle alone isn’t a mollusk group; it describes a feature, not a category. Because the defining feature here is tentacles attached to the head, the best fit is cephalopods.

This question tests recognizing which mollusk group has limbs that originate directly from the head. Cephalopods are defined by having their tentacles and arms attached to the head region, forming a head-foot body plan. This arrangement—tentacles emerging from the head—fits octopuses, squids, and their relatives, and is a hallmark of cephalopods.

Bivalves, like clams and oysters, lack a distinct head and do not possess these head-attached tentacles. Gastropods, such as snails and slugs, do have a head with sensory tentacles, but their body plan centers on a prominent foot and often a shell, not a cluster of limbs arising from the head. The term tentacle alone isn’t a mollusk group; it describes a feature, not a category.

Because the defining feature here is tentacles attached to the head, the best fit is cephalopods.