•  Class Chondrichthyes • (The cartilaginous fishes)

• I. General Overview •  A. 850 species •  B. skeleton of cartilage but there

is extensive calcification, true bone is absent.

•  C. moveable jaws are now present.

•  D. there are now paired fins on dorsal and ventral sides.

•  E. most are carnivorous •  F. most have well developed

olfactory organs •  G. lateral line is present •  H. the skin which is tough and

leathery is covered by placoid scales.

• Class Chondrichthyes •  II. External characteristics •  A. 2 ventral fins, one behind the

others, each with a spine at the end •  1. 2 pectoral fins •  2. 2 pelvic fins •  3. Males have reproductive

appendage called claspers on pelvic fins

•  4. Between pelvic fin is the cloacal opening (anus)

•  B. Caudal fin or tail •  1. assymetrical •  2. Often called a heterocercal tail •  3. Vertebral column extends into

dorsal portion of tail •  C. The nostril opens into a blind

pouch that is the olfactory sac

•  D. Gill slit are anterior to the pectoral fin

•  1. The most anterior slit is modified into a spiracle

•  E. Integument •  1. Tough and leathery in

appearance

•  2. Skin is covered by placoid scales

•  a. hard toothlike structures.

• F. Movement •  1. Heterocercal tail provides

momentum or speed •  2. The other fins are to provide

support and to keep upright.

•  G. Mouth •  1. Transverse slit anterior on

the ventral surface of head •  2. Over jaws are modified

placoid scales to form teeth

• 3. Teeth are directed posteriorly or backward in order to hold and tear prey while slashing head back and forth

•  4. Teeth are loosely attached and one is usually ready to move in when the previous one is lost.

•  5. Oral glands and tongue are poorly modified and in some species absent altogether.

•  6. Flow of water into mouth and out of gill slits aids in pushing food back to esophagus

•  III. Digestive system •  A. Food enters the esophagus by

way of a pharynx. Oxygenated water also passes through this area in route to the gill slits

•  B. Esophagus is just a tube for transporting food to the stomach

•  C. Food enters the stomach via the cardiac sphincter and is stored and begins digesting

•  D. The broken down food then exits the stomach by the pyloric sphincter and enters the intestine

•  E. In the intestines is where most of the food is digested and absorbed (there is no division of the intestines)

•  1. Within the intestines is a spiral valve, this slows the passage of food and increases digestive and absorption surface.

• 2. Intestinal and urogenital ducts (water waste system) empty into the cloaca

– F. What food isn’t absorbed is moved out of the body via the cloaca. This area is also where the reproduction system is located in females.