Which organisms are classic examples of Annelida?

Which organisms are classic examples of Annelida?

• A. Earthworms and leeches
• B. Sea urchins and starfish
• C. Snails and slugs
• D. Insects

Answer: (A)

Annelids are segmented worms, defined by metamerism—the body is built from repeating segments. Earthworms and leeches are classic examples because their bodies clearly show these segments, and they have a true coelom and a closed circulatory system that work across those segments. This combination of segmentation plus the internal body plan is what characterizes Annelida. The other groups belong to different phyla: sea urchins and starfish are echinoderms with radial symmetry and a water vascular system; snails and slugs are mollusks often with a muscular foot and, in many cases, a shell; insects are arthropods with an external exoskeleton and jointed legs.

Annelids are segmented worms, defined by metamerism—the body is built from repeating segments. Earthworms and leeches are classic examples because their bodies clearly show these segments, and they have a true coelom and a closed circulatory system that work across those segments. This combination of segmentation plus the internal body plan is what characterizes Annelida.

The other groups belong to different phyla: sea urchins and starfish are echinoderms with radial symmetry and a water vascular system; snails and slugs are mollusks often with a muscular foot and, in many cases, a shell; insects are arthropods with an external exoskeleton and jointed legs.