KINGDOM ANIMALIA Phylum Chordata Class Chondrichthyes

Class Chondrichthyes 846 species of sharks and rays Date to over 400 mya Cartilaginous endoskeleton Jawed Well-develop pectoral/pelvic fins, powefull tail fin Skin is rough due to numerous placoid scales (constantly worn out/replaced)

The notochord, which is present in the young, is gradually replaced by cartilage. Chondrichthyes also lack ribs, so if they left the water, the larger species's own body weight would crush their internal organs long before they would suffocate. As they do not have bone marrow, red blood cells are produced in the spleen and special tissue around the gonads. They are also produced in an organ called Leydig's Organ which is only found in cartilaginous fishes, although some do not possess it. Another unique organ is the epigonal organ which probably has a role in the immune system. The subclass Holocephali, which is a very specialized group, lacks both of these organs.

Class Chondrichthyes The evolution of jaws is an example of evolutionary modification of existing structures to perform new functions. Jaws are modified gill arches, and allowed the exploitation of new roles in the habitats: predators with powerful jaws. There are two classes of jawed fish: the cartilaginous fish and the bony fish.

They have jaws, lots of teeth, paired fins, and a cartilage endoskeleton.  Cartilaginous fish first appeared during the Devonian Period and expanded in diversity during the Carboniferous and Permian before nearly disappearing during the great extinction that occurred near the end of the Permian.  A large group of cartilagenous fish still survives today and is an important part of the marine fauna. These fish have five to seven gill slits on both sides of the pharynx, and lack the gill covers found in bony fish.

The chondrichthyian body is covered epidermal placoid (or toothlike) scales. Developmental studies show the teeth of sharks are enlarged scales. The largest sharks are filter feeders, not the predators of Hollywood movies. Basking and whale sharks eat tons of crustaceans (small krills, etc.) filtered from the water. Most sharks are fast-swimming, open-sea predators. The great white shark feeds on dolphins, sea lions and seals (and people sometimes). In other words, anything is WANTS to!

Class Chondrichthyes Teeth = enlarge placoid scales Teeth form in actively growing skin areas in mouth just behind upper/lower jaws; skin grows, teeth pushed over edge of jaw and increase in size Teeth worn = reabsorbed or lost In rays, teeth fuse to form bony plates

Class Chondrichthyes Internal fertilization facilitated via unique pelvic claspers on males Anamniote eggs enscapsulated in leathery case or retained in body until birth of living young

Class Chondrichthyes 2 informal groups: differ in body plan and definition Sharks (353 species) Powerful swimmers Mid-water dwelling Solitary predators

2. Rays (456 species) Dorsoventrally flattened enlarged pectoral fin – subject to waves on muscular contraction Bottom-dwelling eat shelled inverts (crush) Rays and skates live on the ocean floor; their pectoral fins are enlarged into winglike fins; they swim slowly. Stingrays have a venomous spine. The electric ray family can feed on fish that have been stunned with electric shock of over 300 volts. Sawfish rays have a large anterior "saw" that they use to slash through schools of fish.

Class Chondrichthyes Most marine, some taxa are estuarine or freshwater Range in size (from 20cm to over 12m) Commercially important in food , cosmeticpharmaceutical, and medical products Estimated 771,400 tons of sharks/rays harvested each year by humans (while only 30 humans-2.6 tons harvested by sharks)