Chondrichthyes are cartilaginous fish and make up only 10% of all fish. Cartilaginous fishes have a skeleton of cartilage, visible gill slits, spiracles, placoid scales, a lateral line organ, and no swim bladder.

Sharks tend to eat the slow, weak, or sick fish in a school. This is important to the ecological balance of an environment because the sharks inadvertently eliminate the weaker animals of a population. Shark reproduction is similar to mammals in that they utilize internal fertilization and give birth to few live young. Examples include nurse shark, spiny dogfish, lemon shark, tiger shark, hammerhead, and sharpnose.

• Eyes
• Nostrils
• Lateral line – detects disturbances in the water
• Barbel – tasting and feeling
• Gill slits – no protective cover
• Dorsal Fin – unpaired keel, keeps fish from rolling like a football
• Anal Fin – unpaired keel, keeps fish from rolling like a football
• Pelvic Fin – paired, keep fish horizontal
• Pectoral Fin – paired, brakes, steering
• Caudal Fin – unpaired, propel and maneuver the fish  all fins are used to maintain mobility, stability and maneuverability
• Scales –placoid. They grow with annual rings like that of a tree. Dermal denticles – small teeth that point towards the tail
• Spiracle – vestigial gill slit
• Clasper – males only

Skeleton is made of cartilage. Backbone made be calcified. No swim bladder – the use the liver instead and the fat and oil produced. The must swim in order to breathe.

Sharks may be scavengers or carnivores. They have very strong senses and may detect minute amounts of fish blood with their nostrils, the lateral line can detect movements in the water and a small group of pores called the ampullae of lorenzini can dectect electrical impulses.

Skates are harmless fish. They take in water from their spiracles and push it out through the gills on the underside of their bodies. They prey on shellfish, worms, and crabs. They have strong jaws to eat.

Rays have a spine with venom that they uses defensively. They are not aggressive, but swimmers are still advised to do the “stingray shuffle” when swimming in the Atlantic.

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