The correct answer is D. Jawless fishes.
Jawless fishes are the most primitive and surely the first of the vertebrates. They are also known as agnathans, which means “without jaws.” Jawless fishes have a long, eel-like body and a single nostril on each side of their head. They lack paired fins and scales, and their skeletons are made of cartilage.
Jawless fishes are an ancient group of fish that have been around for over 500 million years. They are found in both freshwater and saltwater habitats, and they range in size from a few millimeters to over a meter long.
The most common type of jawless fish is the lamprey. Lampreys are parasitic fish that attach themselves to other fish and feed on their blood. They have a round, sucker-like mouth with sharp teeth that they use to attach themselves to their prey.
Another type of jawless fish is the hagfish. Hagfish are also parasitic, but they feed on the flesh of dead fish. They have a long, eel-like body and a slime-producing gland that they use to defend themselves from predators.
Jawless fishes are an important part of the aquatic ecosystem. They are a food source for other fish and animals, and they help to control populations of other fish.
Here is a brief explanation of each option:
- Option A: Frogs are amphibians. Amphibians are vertebrates that live both on land and in water. They have smooth, moist skin and lay eggs in water.
- Option B: Reptiles are amniotes. Amniotes are vertebrates that have a hard shell around their eggs. This allows them to lay their eggs on land, instead of in water.
- Option C: Amphibians are amphibians. Amphibians are vertebrates that live both on land and in water. They have smooth, moist skin and lay eggs in water.
I hope this helps!