Question

Sharks and rays are ________ a. ray-finned fishes c. jawless fishes b. cartilaginous fishes d. lobe-finned fishes

Short answer

Sharks and rays are cartilaginous fishes.

Step-by-step solution

Understand the Options

Sharks and rays belong to a specific class of fishes. We need to understand the types of fishes mentioned in the options: ray-finned fishes have bony skeletons with fins supported by long, thin bones; cartilaginous fishes have skeletons made of cartilage; jawless fishes lack jaws and paired fins; and lobe-finned fishes have fleshy, lobed, paired fins, which are not like the fins of sharks and rays.

Analyze the Characteristics of Sharks and Rays

Sharks and rays are both known for having skeletons made of cartilage rather than bone. This is a distinct characteristic that separates them from other types of fishes like ray-finned or lobe-finned fishes, which have bony structures.

Match the Characteristics to the Correct Option

Given the characteristics of having skeletons made of cartilage, we determine that sharks and rays fall under the category of cartilaginous fishes. This matches option (b) perfectly.

Key concepts

Sharks

Sharks have fascinated humans and scientists for centuries due to their unique traits. They are a diverse group of fish known for their sharp teeth, streamlined bodies, and exceptional sensory capabilities. Unlike most fish, sharks have an extraordinary sense of smell that allows them to detect a drop of blood in a vast expanse of ocean. This sense serves as a crucial tool for their survival and hunting patterns.
Sharks are also known for their cartilaginous skeleton, which distinguishes them from most other fish that have bony skeletons. This skeletal structure provides them with several advantages, including flexibility and reduced weight, which are essential for their fast and agile movements in the water. Moreover, their skins are covered with tiny, tooth-like structures called dermal denticles, helping reduce water resistance and providing protection from predators and rough surfaces.

Cartilaginous Fishes

Cartilaginous fishes, also known as Chondrichthyes, include species such as sharks, rays, and skates. They are distinct from other fish primarily due to their skeletons made of cartilage rather than bone. Cartilage is flexible and lighter than bone, giving these fishes a notable advantage in their aquatic environments.
Some hallmark traits of cartilaginous fishes are their rigid fins, which help in precise movements and control in the water, and a large liver filled with oil that aids buoyancy. This is particularly important as it helps them maintain their position in the water column without a swim bladder, unlike most bony fish. Additionally, they exhibit a reproductive strategy involving internal fertilization, which is quite advanced compared to some other fish species.

• Their teeth are not fixed in their jaws but are embedded in the gums, allowing them to replace teeth easily throughout their lives.
• Many species also show highly developed senses, crucial for navigating their marine environments and hunting.

This group of fishes showcases a perfect blend of evolutionary adaptations that make them well-suited to their marine habitats.

Fish Classification

Fish classification involves understanding the various groups into which fish are divided based on features such as skeletal structure, fin type, and more. Scientists generally categorize fish into three primary classes:

• Agnatha (jawless fishes)
• Chondrichthyes (cartilaginous fishes)
• Osteichthyes (bony fishes)

Sharks and rays belong to the Chondrichthyes class, characterized by their cartilaginous skeletons. On the other hand, the most numerous and diverse fish belong to the Osteichthyes class. These fish have skeletons made of hard bone and include species such as salmon, trout, and goldfish.
Within the bony fish category, we can further break down into ray-finned and lobe-finned fish. Ray-finned fish have webs of skin supported by spines, ideal for a wide array of aquatic environments. In contrast, lobe-finned fish have fleshy fins supported by a central bone—which resemble the limbs of terrestrial vertebrates, hinting at evolutionary links to land animals.
By studying these classifications and the unique features of each group, we gain a clearer understanding of the evolutionary paths and ecological niches occupied by different fish species throughout history.