8. Cartilage fish belong to what class? 9. Name and describe the type of scales present on sharks. 10. Give two ways that sharks remain buoyant. 11. What is the function of the spiral valve? 12. How do sharks breath? Do they have special structures to pump over their gills? 13. Name the Class bony fish belong to.Name the 2 sub classes this class is divided into. 14. Name and describe the type of scales found on a bony fish.

8. Cartilage fish belong to the class **Chondrichthyes**.<br /><br />9. Sharks have **placoid scales**, also known as dermal denticles. These scales are tooth-like structures embedded in the skin, giving it a rough texture. Each scale consists of a basal plate of dentine embedded in the dermis, a pulp cavity, and an outer layer of enamel-like vitrodentine. The scales point backward, reducing friction as the shark moves through the water.<br /><br />10. Sharks maintain buoyancy in two primary ways:<br /><br /> * **Large livers rich in oil:** The oil stored in their livers is less dense than water, providing lift. Different species have varying liver sizes and oil content, influencing their buoyancy.<br /> * **Dynamic lift:** Sharks generate lift by their body shape and by constantly swimming. The shape of their fins and body deflects water upwards, creating an upward force. This is similar to how an airplane wing generates lift.<br /><br />11. The spiral valve is a modification of the ileum (part of the small intestine) in sharks. It increases the surface area for nutrient absorption by slowing down the passage of food and creating a spiral path for it to travel through.<br /><br />12. Sharks breathe by taking in water through their mouths and passing it over their gills. The gills extract oxygen from the water and release carbon dioxide. Unlike bony fish, sharks **do not have opercula** (gill covers) or special muscles to pump water over their gills. Most sharks rely on **ram ventilation**, meaning they must swim constantly to force water over their gills. Some bottom-dwelling sharks can use **buccal pumping**, where they use muscles in their mouths and pharynx to pump water over their gills.<br /><br />13. Bony fish belong to the class **Osteichthyes**. This class is divided into two subclasses:<br /><br /> * **Actinopterygii:** Ray-finned fishes (the vast majority of bony fish).<br /> * **Sarcopterygii:** Lobe-finned fishes (including lungfishes and coelacanths).<br /><br />14. Bony fish typically have either **cycloid** or **ctenoid** scales.<br /><br /> * **Cycloid scales:** These are thin, overlapping scales with a smooth outer edge. They are arranged in concentric rings, similar to tree rings, which can be used to determine the age of the fish.<br /> * **Ctenoid scales:** These are also thin and overlapping but have tiny comb-like projections called ctenii on their posterior edge. These projections create a rough texture and are thought to reduce drag in the water.<br />