Figure 8 01 Characteristics of Subphylum Vertebrata A

Figure 8. 01

Characteristics of Subphylum Vertebrata A notochord that has developed into a spinal cord protected by vertebrae. Also contain a head with a brain.

Significance of Class Agnatha This is the class of the jawless fish. Species include lampreys and hagfish. Organisms in this class are significant because they may represent the ancestor of bony fish/sharks. Scientists theorize that during the Cambrian period the first of three gill arches on a jawless fish evolved into the first jaws. Having jaws allowed vertebrates to become very successful predators. Having jaws put organisms in class Chondrichthyes (sharks and rays) and class Osteichthyes (bony fish) near the top of marine food webs.

Figure 8. 02

Characteristics of Sharks and Rays Class Chondrichthyes includes sharks, rays and their close relatives. Sharks and rays don’t look similar on the outside, but share a basic anatomy that classifies them together. Sharks and rays are jawed fish, that lack a swim bladder, and have cartilaginous skeletons.

Special Attributes of Sharks and Rays Sharks and rays are successful predators: They have cartilaginous skeletons. This characteristic saves energy. Saving energy is one of the things that have made them successful predators. Sharks have a sense of smell that detect incredibly diluted substances. (one drop of blood in a mile of water) Sharks have a “conveyor belt” of multiple rows of teeth. They swing into place as old teeth wear out and fall away.

Special Attributes of Sharks and Rays Sharks and rays have other interesting characteristics: Both have lateral lines – lines of sensory organs along the length of the body that detect water motion and vibrations. Unique to sharks and rays 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. 5 -7

Special Attributes of Sharks and Rays New type of reproductive strategy. Sharks and rays produce fewer, but more mature offspring. Most fertilize their eggs internally. A few shark species are ovoviviparous – the eggs hatch within the mother’s body. They give birth to live young rather than egg cases.

The largest fish in the ocean. Shark size ranges from hand-sized to the whale shark – the largest fish in the ocean. Whale sharks can reach 14 meters (46 feet). Basking sharks can reach 10 meters (33 feet). Megamouth sharks can reach 6 meters (20 feet). All three are filter feeders that consume plankton.

Visiting The Georgia Aquarium!

Figure 8. 14 a

Special Attributes of Rays Superorder Batidoidimorpha of subclass Elasmobranchii consists of the rays, which includes skates and guitarfish. Ray anatomy is well suited to life on sandy bottoms or midwater. Specially adapted to life in midwater are the eagle ray and manta ray. Pectoral fins have become “wings” that stretch forward over the gills and are fused to the sides of the head. Shoulder girdles are flattened and many bones are fused together for rigidity. No longer need a tail for swimming, the tail has become a defensive whip in some species. Rays literally fly through the water. The largest rays are mantas with wingspans exceeding 8 meters (26 feet). Like the largest shark, the mantas feed on plankton.

Figure 8. 12 a

Figure 8. 26

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Figure 8. 05 b

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Figure 8. 08 a