🦈 Class Chondrichthyes (Cartilaginous Fishes)

Examples

• Sharks

• Skates

• Rays

• Ratfishes

---

1. Skeleton

• Made entirely of cartilage, not bone.

• Body covered by placoid scales (tooth-like structures) called denticles, giving a rough texture and reducing drag while swimming.

---

2. Fins

• Paired fins: pectoral and pelvic fins.

• Two dorsal fins present (on the back).

• These fins help in stability and steering.

---

3. Respiration

• Have spiracles—small openings located just behind the eyes—used for breathing.

• No swim bladder (unlike bony fishes); they rely on dynamic lift from fins and oil in the liver to maintain buoyancy.

---

4. Circulatory System

• Possess a single-circuit heart with one atrium and one ventricle.

• Blood passes through the heart once per circuit (typical of fish).

---

5. Reproduction

• Fertilization is internal.

• Many species are ovoviviparous (eggs hatch inside the mother’s body).

---

✅ Key Adaptations

• Streamlined body for fast swimming.

• Cartilaginous skeleton offers flexibility and lightness.

• Highly developed sensory organs for detecting prey.

•