The SharksClass Chondrichthyes

Class Chondrichthyes• Includes sharks, skates and rays

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

Characteristics• Cartilage instead of bone (chondros =

cartilage)• Lighter, more flexible• Jaws and paired fins (unlike Class Agnatha)

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

External Anatomy

Internal Anatomy

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

Buoyancy• 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

liver

Senses• Excellent sense of smell – nostrils only for

smell, not breathing• Simple, internal ear to hear low-frequency

vibrations

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

Reproduction

• 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

claspers

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 canwork independently and in oppositionto each other

Feeding

• Many are predators– Eat fish, marine mammals– Speed

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

Shark Attacks

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

Shark Attacks

• Great whites most dangerous – up to 23 feet and 3,000 pounds

• Other dangerous species: mako, tiger, hammerhead

Symbiosis

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

Human Uses

• Food– Steaks– Shark fin soup

• Vitamin A in livers• Skin – leather = shagreen• Overfished

Rays and Skates

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

Rays and Skates

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