Question

1. which structure gives echinoderms their characteristic spiny skin?

○ a sieve plate
○ an ossicle
○ an arm
○ a tube foot

Explanation:

To solve this, we analyze each option:

• A sieve plate is related to phloem in plants, not echinoderms.
• Ossicles are small calcareous plates in echinoderms' endoskeleton, which protrude through the skin, giving them the spiny appearance.
• An arm is a body part for movement/feeding, not related to spiny skin.
• Tube feet are for locomotion/feeding, not for spiny skin.

Answer:

B. an ossicle