Cartilaginous Fishes

Cartilaginous Fishes Class Chondrichthyes

Cartilaginous Fishes This group includes: sharks, rays, skates, and ratfishes.

Characteristics of Cartilaginous Fishes Have a skeleton made of cartilage (lighter and more flexible than bone). Possess moveable jaw and the mouth is almost always ventral to the head (underneath). Pair of lateral fins for efficient swimming. Skin has placoid scales (made out of the same material as their teeth) that gives the skin a sandpaper-like feel.

Placoid Scales

Shark Body Design • Sharks are tapered to a point on each end to allow them to easily slip through the water. • The caudal tail is well developed and powerful • Heterocercal – the upper lobe is longer than the lower lobe

Shark Body Design Two dorsal fins – the first is triangular. Large paired pectoral fins 5-7 gill slits are located behind the head and are present on each side of the body.

Sharks have other interesting characteristics: • Lateral lines – lines of sensory hair cells along the length of the body that detects water motion and vibrations. • Unique to elasmobranchs is electroreception • the ability to sense minute electricity created by muscles and nerves. • Sharks and rays have organs called ampullae of Lorenzini which you can see as visible pits near their snouts used to detect the electrical current.

Shark Body Design • The powerful jaws have rows of numerous sharp, normally triangular, teeth. • Any lost or broken tooth is replaced by another, which slowly shifts forward from the row behind it.

Shark Body Design Not all sharks share the same general body plan…

…Hammerhead Sharks… • Flattened heads • Eyes and nostrils are located on the ends of bilateral extensions • Head functions as a rudder

…Sawsharks… • Head is extended into a long, flat blade armed with teeth along the edges.

…Thresher Shark… • The upper lobe of the caudal fin is very long, which is used to herd and stun schooling fish.

The Sizes of Sharks Sizes vary according to species

…Spined Pygmy Shark… • Grows to no longer than 25 cm • (The length of the handle of our fish nets!)

…Whale Shark… The largest of all fishes and can be as long as 18 m (60 feet)! They are filter feeders.

…Basking Shark… Second in size only to whale shark, can be up to 15 m (50 feet) in length. They are also plankton eaters.

…Great White Shark… Can be as large as 6 m (20 feet).

Shark Habitats Found throughout the oceans at almost all depths. More prevalent in tropical waters. Primarily marine, but some travel far up rivers.

Rays and Skates • Rays and skates have flattened bodies • Often live on the bottom • Fish that live on the bottom are called demersal. • ONLY rays and skates have gill slits (always 5 pairs) on the underside of the body.

Rays and Skates • Pectoral fins are flat and look much like wings and are fused to the head.

…Stingrays Stingrays (and their relatives) have a whip-like tail usually equipped with stinging spines at the base for defense.

Stingrays Feed on clams, crabs, small fishes, and other small animals that live in sediment Expose their food by moving the sediment with their pectoral fins.

…Electric Rays (Torpedo Rays) Rays with special organs on each side of the head that produce electricity. Can deliver shocks of up to 200 volts to stun fishes they eat and discourage predators.

…Eagle, Manta and Devil Rays Don’t spend their whole life on the bottom and seem to “fly” through the water using their pectoral fins like wings. Mantas actually feed in midwater on plankton.

…Manta Ray… Manta rays can be up to 7 m (23 feet) wide!

Skates Skates are similar to rays in appearance and feeding habits. Lack a whip-like tail and stinging spines. Skates lay egg cases, while rays give birth to live young.

Ratfishes Cartilaginous fish that are grouped separately because of their unique features. Have gill slits covered by a flap of skin. Some have a long rat-like tail. Feed on bottom dwelling crustaceans and molluscs.

Ratfishes

Cartilaginous Fishes