Question

Which of the following vertebrate classes is jawless?

• A. Chondrichthyes
• B. Osteichthyes
• C. Trygon & Aves
• D. Cyclostomata

Hint:

Remember: \[ \boxed{\text{Cyclostomata} \rightarrow \text{Jawless vertebrates}} \] Examples: \[ \boxed{\text{Petromyzon and Myxine}} \] All other classes of fishes possess true jaws.

Answer 1

The Correct Option is D

Concept: Vertebrates are classified into different classes based on the presence or absence of jaws, type of skeleton, and other anatomical features. Cyclostomata are the only living jawless vertebrates. Examples include: \[ \boxed{\text{Petromyzon (Lamprey), Myxine (Hagfish)}} \]

Step 1: Understand the characteristics of Cyclostomata.
Cyclostomata possess:

• Circular sucking mouth.

• Absence of jaws.

• Cartilaginous cranium.

• Elongated eel-like body.
Hence, they are called jawless fishes.

Step 2: Analyse the remaining options.

• Chondrichthyes possess jaws and cartilaginous skeleton.

• Osteichthyes possess jaws and bony skeleton.

• Trygon (stingray) and birds also possess jaws.
Therefore, none of these groups are jawless.

Step 3: Choose the correct option.
Only Cyclostomata are jawless vertebrates. Therefore, \[ \boxed{\textbf{Option (D)}} \] is the correct answer.