1. The Sharks
Class Chondrichthyes

2. Class Chondrichthyes
• Includes sharks, skates and rays

3. Class Chondrichthyes
• Inhabited earth for 280 million
years (twice as long as dinosaurs)
• 350 species of sharks
• 320 species of rays
• Found worldwide at all depths –
almost all marine

4. Characteristics
• Cartilage instead of bone (chondros =
cartilage)
• Lighter, more flexible
• Jaws and paired fins (unlike Class Agnatha)

5. Characteristics
• Streamlined body – torpedo shape - fusiform
• Placoid scales – denticles – small tooth-like
plates – like sandpaper
• Counter-shading – dark on top, light on
bottom – form of camouflage

6. External Anatomy

7. Internal Anatomy

8. Respiration
• 5 to 7 gill slits
• No operculum covering gill slits
• Water passes over gills, oxygen diffuses into
blood, carbon dioxide out
• Some pump water through mouths, some,
take in water through spiracle, others keep
swimming

9. Buoyancy liver
• No swim bladder
• Store oil in large liver
• Heterocercal tail – asymmetrical – creates lift
• Horizontal pectoral fins also provide lift
• Cannot swim in reverse like bony fish

10. Senses
• Excellent sense of smell – nostrils only for
smell, not breathing
• Simple, internal ear to hear low-frequency
vibrations

11. Senses
• Electroperception – ability to detect weak
electric currents
– Ampullae of Lorenzini – in skin pores – find prey
and for migration
• Lateral line – stretches from head to tail –
fluid- filled sensory canals - sensitive to
vibrations

12. Reproductio
n
claspers
• Separate sexes
• Usually internal fertilization – rare in fish
• Claspers – male structures to transfer sperm to
female
• Some sharks give birth to live young
• Some sharks lay few, large eggs - mermaid’s
purse
– Durable case
– Large yolk - nutrition
– Well-developed young hatch

13. Feeding
• Ventral mouth
• Teeth – specialized denticles
• 6 – 20 rows deep
• Easily lost and replaced – up to 50,000 in a
lifetime
• Hinged jaws – upper and lower can
work independently and in opposition
to each other

14. Feeding
• Many are predators
– Eat fish, marine mammals
– Speed

15. Feeding
• Some eat plankton
– Whale shark – largest fish – up to 60 feet long
– Filter plankton with open mouth
– Low on food web
• Some are scavengers

16. Shark Attacks
• Rare
• Average of 6 per year worldwide
• Very few species attack humans
• Usually mistake humans for seals

17. Shark Attacks
• Great whites most dangerous – up to 23 feet
and 3,000 pounds
• Other dangerous species: mako,
tiger, hammerhead

18. Symbiosis
• Remora - suckerfish
• Mutualistic symbiotic relationship with shark
– Picks up scraps and feeds on external parasites

19. Human Uses
• Food
– Steaks
– Shark fin soup
• Vitamin A in livers
• Skin – leather = shagreen
• Overfished

20. Rays and Skates
• Flattened bodies
• Broad, wing-like pectoral fins
• Glide or “fly” through water
• Both eyes on top of head

21. Rays and Skates
• Ventral mouth with “teeth” for
scavenging and crushing invertebrates
• Largest feed on plankton
• Usually associated with ocean bottom
• Most not harmful