Question

Which of the following statements are CORRECT?

• A. Mytilus represents byssally attached bivalves
• B. Nautilus is the only living cephalopod genus with a coiled external shell
• C. The cidaroids are the only echinoid group still living
• D. Trilobites did not moult

Answer 1

The Correct Option is A, B

To solve this question, we need to evaluate the factual correctness of each statement provided in the options:

1. Mytilus represents byssally attached bivalves: This statement is correct. Mytilus, commonly known as mussels, are a type of bivalve mollusk that attach themselves to surfaces using byssal threads. These threads are strong, silk-like fibers that allow them to anchor to rocks, piers, or other substrates.
2. Nautilus is the only living cephalopod genus with a coiled external shell: This is also a correct statement. The Nautilus is a genus of cephalopods that have retained their coiled, external shell, a feature that is otherwise lost or internalized in all other living cephalopod species like octopuses, squids, and cuttlefish.
3. The cidaroids are the only echinoid group still living: This statement is incorrect. Cidaroids are one group among many within echinoids (sea urchins). There are several echinoid groups still extant today, including both regular and irregular echinoids.
4. Trilobites did not moult: This statement is incorrect. Trilobites, an extinct group of marine arthropods, did indeed moult their exoskeleton as they grew, a process similar to that seen in modern arthropods like crustaceans and insects. Moulting is a characteristic feature of arthropods.

Based on the evaluation of each statement, the correct answers are:

• Mytilus represents byssally attached bivalves
• Nautilus is the only living cephalopod genus with a coiled external shell