• 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.