Question

Mr. Morales is teaching a lesson on classification. He says that spiders are classified as a different group than insects because they have eight legs instead of six legs. He explains that spiders evolved first. Mr. Morales also says that having eight legs is the derived trait that separates the two groups. Antonio thinks Mr. Morales is wrong. Which piece of information is Antonio considering?
Spiders do not have eight legs.
Insects do not have six legs.
If spiders evolved first, six legs is the derived trait.
Spiders do not have derived traits, since they evolved first.

Answer 1

Answer:

C. If spiders evolved first, six legs is the derived trait.

Explanation:

A derived trait is a characteristic that is present in a species but was absent in the common ancestor of this species.

Spiders evolved from a crab-like ancestor and, although crabs are decapods, they possess eight walking legs and two claws. As insects evolved after spiders, the 'new' or derived trait that was absent in the ancestor would be having six legs.

Therefore, in this scenario, Mr. Morales states that spiders evolved before insects, which indicates that the trait of six legs is a derived trait from the last common ancestor, a characteristic that separates arachnids from insects.