Question

Fossils from which of the following invertebrate classes show pentameral symmetry?

• A. Echinoidea
• B. Anthozoa
• C. Cephalopoda
• D. Trilobita

Hint:

All echinoderms (e.g., starfish, echinoids) show pentameral symmetry — a key diagnostic fossil feature.

Answer 1

The Correct Option is A

Step 1: Understanding pentameral symmetry.
Pentameral (five-fold) symmetry is a characteristic feature of echinoderms, where body parts are arranged in multiples of five around a central axis.
Step 2: Evaluating the options.
(A) Echinoidea: Class within Echinodermata (e.g., sea urchins, sand dollars) — exhibits pentameral symmetry.
(B) Anthozoa: Includes corals and sea anemones — radial symmetry, not pentameral.
(C) Cephalopoda: Bilaterally symmetrical mollusks (e.g., squids, nautilus).
(D) Trilobita: Bilaterally symmetrical arthropods.
Step 3: Conclusion.
Therefore, fossils of Echinoidea show pentameral symmetry.