• Absence of jaws.
• These organisms lack the paired fins (pelvic and pectoral).
• Skeleton made of cartilage.
• Round eel-like body with a compressed caudal fin.
• Soft skin devoid of scales.
• They lack a swim bladder and gill covers (operculum).
• 7 gill slits on each side of the head.
• The lamprey are parasitic and the hagfish are scavengers.
• Ectothermic ( animals that cannot control their body temperature).
• External fertilization. Oviparous ( egg laying)
• Marine and fresh water species are found.
• Lateral line
• Two chambered heart
• Gills used for respiration
• No external ears
• No eye lids

Class Chondrichthyes: ( Sharks, Rays, and Skates).

General Characteristics:

• Skeleton made of cartilage.
• Body covered with triangular Placoid scales.
• Ventral,subterminal mouth with several rows of triangular teeth.
• Large caudal fin with the dorsal section larger than the ventral one.
• Paired fins ( pectoral and pelvic), are stiff and nonflexable.
• They lack a swim bladder.
• Ectothermic
• Internal fertilization. Ovoviviparous ( developing egg kept inside the female for protection and does not live off of the parent).
• Marine organisms only.
• Lateral line
• Two chambered heart
• Gills used for respiration
• No external ears
• No eye lids

Class Osteichthyes: ( Tuna, Carp, Salmon, and Sturgeons).

General Characteristics:

• Skeleton made of bone
• Lateral line
• Two chambered heart
• Operculum covering the gills.
• Swim bladder
• Ectothermic
• Paired fins made of rays and spines,or lobed fins lacking the rays and spines.
• Various types of scales (ctenoid,ganoid, or cycloid).
• Marine and fresh water species.
• Gills used for respiration
• External fertilization. Spawning. Oviparous.
• No external ears
• No eye lids.

1. Olfactory Lobes : Functions in smell.

2. Cerebrum : Functions in muscle movement, intelligence, instinct, and will power.

3. Optic Lobes : Functions in eye sight.

4. Cerebellum : Functions in muscular coordination.

5. Medulla Oblongata : Functions in involuntary responses ( heart beat, breathing, and digestion ).

6. Spinal Cord : Functions in transport of nerve impulses to and from the brain.

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