1. Sharks

2. Classification Kingdom Animalia Phylum Chordata Class Chondrichthyes
Subclass Elasmobranchii
Superorder Selachimorpha
Known as “sea dogs” until the 16th century
Name “shark” may have come from the Yucatec Maya

4. Evolution Earliest sharks evolved 450 million years ago
Today – 440 species
Smallest – dwarf lanternshark (7 in)
Largest – whale shark (largest fish – 40 ft)

5. Skeleton No bones Use cartilage and connective tissue
Strong , but ½ the density of bone
Reduces weight  saves energy
Cartilage may be calcified
“bone-like”
No functional rib cage
Must stay in water

6. Jaw Covered in a layer of tesserae Complex rigid surface
Single tile in a mosiac
Tiny hexagonal plates
Crystal blocks of calcium salts
Most sharks have one layer of tesserae
Great white sharks – up to five

7. Teeth Embedded into gums rather than the jaw
Arranged into 2-3 rows of teeth
Continuously replaced
Gums “conveyor belt” them to the front
Can shed 35,000 teeth in a lifetime
Tooth characteristics determined by diet
Very important to fossil record – all that remains

9. Tooth Anatomy

10. Fins
Supported by unsegmented rays composed of proteins

11. Tail (Caudal) Fins 6 different designs found in sharks
Shapes evolved due to different habitats and diets
All are heterocercal in design
Top is longer than the bottom

13. Buoyancy No swim bladder Large livers Up to 30% of body mass
Contain squalene
Oil that is less dense that water
Sharks hunted for this oil
Put in capsules as a health supplement
Used in vaccines
Also available from plant sources

14. Respiration
Oxygen removed as water passes through the mouth and over the gills
Process known as ram ventilation
Most sharks can pump water over their gills while at rest
Some cannot (obligate ram ventilators)
Gills not covered (as with most fish)

15. Circulation
Sharks have a two chambered heart

16. Thermoregulation Most sharks are poikilothermic (cold blooded)
Body temp is that of the environment
Family Lamnidae sharks can raise their body temp higher than the water temp (includes mako and great white)
Homeothermic
Strip of red muscle in center of body attached to the rete mirabile (miraculous net)

17. Rete Mirabile
Uses countercurrent flow design

18. Osmoregulation Living in salt water Large production of urea
Shark’s tissues isotonic (in balance with) the sea water
So, few sharks can live in fresh water
Bull sharks can change their kidney funtion to excrete the urea

19. Senses – Smell Very keen olfactory sense
Can detect one part per million of blood in sea water
Even greater attraction to chemicals found in guts of organisms
Leads sharks to sewage outfalls

20. Olfactory Bulbs (in pink)

21. Senses – Sight Eyes similar to most vertebrates
Well adapted to the dark marine environment
Use a tapetum lucidum (bright tapestry)
Reflects light back through the retina to increase amount of useable light
Humans do the same (eyeshine in a photo)
Can contract and dilate their pupils

22. Senses – Sight Sharks have eyelids, but don’t blink
Water cleanses eyes
Use nictitating membranes
Covering that moves over eyes to protect them during attacks on prey

24. Senses – Hearing May be able to hear prey many miles away Hard to test
Small opening on each side of the head
Leads to the inner ear
Sense vibrations among the water molecules

26. Senses – Hearing Lateralis system
System of canals within the lateral line
Runs the length of the body
Pores expose water to the system
Contains sensory cells with hair-like projections
Also helps with balance and movement

27. Lateralis System

28. Senses – Electroreception
Sharks can detect electromagnetic fields produced by all living organisms
Sharks have the greatest electrical sensitivity of any organism
Helps them find prey (even under the sand)
Use Ampullae of Lorenzini
Electrorecptor organs
Hundreds to thousands per shark

29. Pores (on a tiger shark)

30. Senses – Electroreception
Ocean currents travel through the magnetic field of the earth
Creates electric fields
May allow sharks to navigate the world’s oceans
Allows sharks to detect temperature gradients