Which organism is NOT typically considered a mollusk?

Which organism is NOT typically considered a mollusk?

• A. Clam
• B. Snail
• C. Octopus
• D. Earthworm

Answer: (D)

Mollusks are a diverse group that typically share a mantle, a muscular foot, and a visceral mass, with many having a shell produced by the mantle. Among the options, clams and snails are classic mollusks, and a cephalopod like the octopus is also a mollusk, even though it lacks a heavy external shell in many species. The earthworm, however, is not a mollusk. It belongs to the phylum Annelida and has a segmented body with setae (bristles) and no mantle or shell. Its body plan and mode of movement are organized around annelid characteristics rather than molluscan ones. So the organism not typically considered a mollusk is the earthworm.

Mollusks are a diverse group that typically share a mantle, a muscular foot, and a visceral mass, with many having a shell produced by the mantle. Among the options, clams and snails are classic mollusks, and a cephalopod like the octopus is also a mollusk, even though it lacks a heavy external shell in many species.

The earthworm, however, is not a mollusk. It belongs to the phylum Annelida and has a segmented body with setae (bristles) and no mantle or shell. Its body plan and mode of movement are organized around annelid characteristics rather than molluscan ones. So the organism not typically considered a mollusk is the earthworm.