sharks, skates, rays

shark

ray skate

shark

460+ species

Streamlined body

Cartilaginous skeleton

Oil in Liver

Must swim continuously

Sharks

Sharks have a head, a middle called a trunk, and a tail.

water enters spiracles caudal fin

… and exits through 5to 7 pairs of gill slits

heterocercal tail

teeth are shed and replaced

Different kinds of sharks havedifferent kinds of tails.

Predators with teeth!

Hammerheads are aggressive hunters, feeding on smaller fish, octopuses, squid, and crustaceans. They do not actively seek out human prey, but are very defensive and will attack when provoked.

Nurse sharks prefer to dwell near the sea floor in the warm, shallow waters of the western Atlantic and eastern Pacific oceans.

The mouthy basking shark is a filter-feeder. It is the second-largest shark, after the whale shark, reaching lengths up to 33 feet (10 meters).

Sharks’ teeth are modified placoid scales

… but the largest sharks filterplankton (free floating, mostly

microscopic organisms)

maximum length: 15.2 m but most <10 m

The whale shark filters plankton

How sharks (almost) achieveneutral buoyancy

Cartilaginous skeleton (bone is dense)• Pectoral fins, surface of the head and heterocercal tailprovide lift• Large livers with large quantities of lipids (sp. gr.= 0.90-0.92)and squalene (sp. gr. = 0.86). (Specific gravity of seawater = 1.026.)… but are still negatively buoyant andmust swim continuously

Most sharks are viviparous!

• oviparous – eggs laid outside the

mother’s body

• ovoviviparous – mother retains

eggs in uterus; embryo nourished

by egg yolk; young born alive

• viviparous – embryos develop in

the uterus nourished by the

mother’s blood through a placenta

Direct development:a shark pup emerges from its egg.

Despite their rows of ragged teeth and vicious appearance, sand tiger sharks are actually rather docile, usually attacking humans only in self-defense.

Confirmed Unprovoked Shark AttacksConfirmed Unprovoked Shark Attacks

• Florida – 717 Fatal-11• Hawaii – 129• California – 114 Fatal-10• South Carolina – 82 Fatal-2• North Carolina – 52 Fatal-3• Texas – 39 Fatal-3• Oregon – 26• Delaware – 4• Maryland - 0• Total in USA from 1837-2014:

1,052Source: Florida Museum of Natural History

Skates and rays: cartilaginous fish

collectively known as “batoids”

What is the difference between skates and rays?

Rays are kite-shaped with streamlined tails

Skates have fleshy tails with small fins

Clearnose Skate

Sting ray with spine (modified placoid

scale) with venom gland at base.

skate

Manta ray: a plankton feeder

6 m

All skates lay eggs;rays are ovoviviparous!

Mermaid’s purse (skates)

Rays• fewer species• long, thin tail without fins• stingray tail armed with spines• ovoviviparousSkates• more species• thicker tail with fins• horns on tail• oviparous