Phylum Chordata (Vertebrates)
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Class Agnatha = jawless fishes = lampreys, hagfishes
Class Chondrichthyes = fishes with cartilage skeletons = sharks, skates, rays
Class Osteichthyes = fishes with bony skeletons = tuna, halibut, sea horses, etc…
Class Reptilia = Crocodiles, turtles, sea snakes, marine iguanas
Class Aves = albatrosses, pelicans, gulls, penguins
Class Mammalia = Whales, seals and sea lions, otters
Phylum Chordata
- Less than 10% of animals are vertebrates
- Have a backbone
- Internal skeleton
o Uninterrupted support during growth
o Protects vital organs
o A place for muscles to attach
o Skull to house the brain, eyes and other sense organs
Fishes are the most successful vertebrates
o Possess gills for breathing and fins for swimming
o More species of fishes than all other chordate classes combined
o Measure from ½ inch to 60 feet
o Weigh from 0.004 ounce to 45 tons (90,000 pounds)
o Some can reach short bursts of 70 miles per hour…some hardly ever move
o Cold-blooded
o 60% live in sea-water
Class Agnatha = jawless fishes = lampreys, hagfishes
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most primitive of all fishes
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lack jaws, scales and paired fins
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feed using round, sucking mouths
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thick snake-like bodies
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gill slits
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surrounded by organs sensitive to touch and smell
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eyes are covered by thick skin
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Hagfish
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Feed on dead or dying fishes
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Live in burrows they dig in muddy bottoms in cold water
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Maximum length of 2.6 feet
Lamprey
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Primarily freshwater fishes
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Attach to other fishes and suck their blood
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Also eat invertebrates
Lamprey mouth
Class Chondrichthyes = fishes with cartilage skeletons = sharks, skates, rays
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Have a skeleton made of cartilage (lighter and more flexible than bone)
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Rough skin covered by placoid scales
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Paired lateral fins for efficient swimming
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Most possess movable jaws
Sharks
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“living fossils” – been around for 100 million years
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350 species
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Size range: dwarf dog shark = 7 inches to Whale Shark (a filter feeder)
up to 60 feet long.
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Most sharks swim continuously, forcing water through the mouth and
over the gills.
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When caught in nets so they cannot force water in, they “drown”.
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Some sharks rest on bottom (example: nurse sharks)
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Rows of numerous, sharp teeth (often triangular)
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A lost or broken tooth is replaced
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Exceptions to the rules: Hammerhead sharks, thresher sharks , Sawsharks
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Found in all oceans at all depths
SHARK FACTS
Life Cycle
Average life span of a shark: Less than 25 years
Longest living shark species: Spiny dogfish, 70-100 years
Birth: Sharks give birth to their young in one of three different ways:
1. Some sharks lay egg cases with developing embryos inside. These sharks are called oviparous (born from an
egg).
2. Other sharks carry young internally that are nourished by a placenta. They are deemed viviparous (born live).
3. Finally, some sharks bear young that develop internally but without attachment to the mother, some within egg
cases. These sharks are ovoviparous (born live from an egg).
Gestation period: From nine months to as long as two years
Number of offspring: Varies from one to up to 100, as observed in the tiger shark (Galeocerdo cuvier)
When sharks stop growing: Never
Shark Superlatives
Largest Shark: The whale shark (Rhincodon typus) is the largest fish in the world, measuring up to 50 feet long.
Smallest Shark: Mature males of the dwarf dogshark (Etmopterus perryi) do not exceed seven inches in length.
Average swimming speed of a shark: About a yard per second
Fastest clocked speed: In sudden, brief bursts, the lemon shark (Negaprion brevirostrus) can attain speeds approaching
20 mph; mako sharks are thought to be even faster.
Youngest shark to bite a human: A marine biologist, while probing the uterus of a pregnant sand tiger shark, was bitten
by an unborn pup.
The strongest shark bite: The greatest force of a shark bite ever recorded measured 132 pounds of force between the
jaws of a dusky shark (Carcharhinus obscurus).
Largest egg in the world: An egg case of the whale shark found in the Gulf of Mexico measured 12 by 5.5 by 3.5 inches.
Most travelled shark: A blue shark (Prionace glauca) tagged off New York was recaptured 16 months later off Brazil,
3,740 miles away.
Freshwater shark: Alone among the sharks, the bull shark (Carcharhinus leucas) is frequently found far up rivers.
Most exciting recent discovery of an unknown shark: In 1976 and 1984, respectively, two specimens of a 15-footlong, plankton-feeding shark were caught in the Pacific. To date at least ten specimens of this new species, whose gaping
mouth inspired the name "megamouth," have been found.
Lowest note a shark can hear: 10 Hertz (or 1.5 octaves below the lowest key on the piano). The lowest note a human
can hear is 25 Hertz, so we miss out on some of the very low frequencies that sharks can detect.
Highest note a shark can hear: 800 Hertz (or G above High C on the piano), so humans can hear many high sounds
that sharks cannot.
The Human Factor
Worldwide shark attack rate: Less than 100 a year, with only 25 to 30 fatalities. Given the number of people
who spend time in the ocean, this is low.
Greatest threat to sharks: Humans
Number of sharks killed by fishers each year: 30 to 100 million
Percentage of shark species threatened with extinction: Up to 80
Information from: http://www.pbs.org/wgbh/nova/sharks/
Shark Anatomy
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tail (caudal) fin is well developed and powerful
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Upper lobe is longer than the lower lobe
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The tail fin is the shark's engine room, providing the power it needs to speed through the water. It's tough if not
impossible to assess the speed of sharks in the wild, but captive sharks exhibit cruising speeds of between 1.2
and 3 miles per hour. The mako, great acrobat of the shark world, has been known to leap almost 20 feet out of
the water. Such a height, tests have shown, would require a starting speed of 22 miles per hour.
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Two dorsal fins: The rigid first dorsal fin serves as a stabilizer, while the second dorsal fin found on some species aids
in rolling.
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Paired pectoral fins: Like wings on an airplane, the low-slung pectoral fins provide the shark with a planing surface to
aid lift during swimming. The pectorals also help in steering and turning and are used to brake forward motion. For all
their swimming prowess, sharks, unlike bony fishes, cannot swim in reverse (though some can use their fins to "crawl"
backwards).
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Spiracle: Contrary to popular thought, not all sharks have to keep swimming to breath. Some, like the whitetip reef
shark, sit still on the seafloor for long periods, breathing just fine. Many bottom-dwelling species, whose mouths are
often pressed to the seabed, inhale through a vestigial gill called a spiracle, found just behind the skull on the upper part
of the head.
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Lateral Line: Stretching from head to tail down the flanks of sharks, the lateral-line system consists of fluid-filled
sensory canals with tiny, hair-like receptors. These are similar to the ampullae of Lorenzini but are sensitive to
vibrations. Acting like a body-length ear, the system helps sharks and other fish sense objects in the ocean. To them, the
lateral line, which has been dubbed "distant touch," is like having a long arm with which to touch a rock or another fish.
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Cartilage: Ancient sharks probably had some bone in their skeletons but gained no evolutionary advantage from it. So
over time they switched to cartilage, which is the stuff that makes up human ears and noses. Since cartilage is less dense
and more elastic than bone, it aids sharks in buoyancy and maneuverability. Sadly for paleontologists, cartilage doesn't
preserve well, and fossil skeletons are as rare as fossil teeth are numerous.
Rays
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450-550 species
Flattened bodies
live on the bottom
5 pairs of gill slits on ventral (bottom) side of body
Pectoral fins are flat and greatly expanded making
them look like wings and fused with the head
 Eyes on top of the head
 Stingrays (and their relatives the eagle, cow-nosed and bat rays) – have a whip-like tail with long stinging spines at the base
for defense. Poison glands produce venom, which can be serious.
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Bury themselves in the sand for camouflage
o Feed on clams, crabs, small fishes and other small animals
 Electric rays have special organs on each side of their head that produce
electricity.
 Manta and Devil rays “fly” through the water
o feed on plankton
o have been observed leaping out of the water
o can grow up to 20 feet wide
Class Osteichthyes = fishes with bony skeletons = tuna, halibut, sea horses
 A skeleton made of bone
 20,000 species = 96% of all fishes and ~50% of all vertebrates
 a great deal of variation in size, shape, color, feeding habits, and behavior.
 Approximately 58% (about 13,630) of all species of bony fishes live in marine environments. Although only 0.01
% of the earth's water is fresh water, freshwater fishes make up approximately 42% (about 9,870) of fish species.
 Bony fishes inhabit almost every body of water. They are found in tropical, temperate, and polar seas. Bony fishes
exist in fresh water, seawater, and brackish environments.
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Some species of bony fishes live as deep as 6.8 mi. in the abyssal oceans. Other species inhabit lakes as
high as 3.1 mi. above sea level.
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Some species of bony fishes aren't limited to one particular ecosystem. Diadromous bony fish species
migrate between fresh and saline environments.
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The desert pupfish (Cyprinodon macularius) lives in small hot springs of California. It can tolerate
temperatures greater than 126ºF.
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At the opposite extreme, some species of bony fishes can survive freezing as long as their body fluids
remain unfrozen. The arctic cod (Boreogadus saida) can survive temperatures as low as 28ºF.
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Some bony fishes can tolerate high salinity levels. Seawater has a salinity level averaging 35 ppt (parts
per thousand). Some species of gobies can tolerate salinity levels as high as 60 ppt.
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In general, fishes rely on oxygen dissolved in water for respiration.
 Some species of bony fishes require large amounts of dissolved oxygen. The brown trout (Salmo
trutta) requires up to 11 mg of dissolved oxygen per liter.
 Misgumus fossilis, a type of loach, can survive in as little as 0.5 mg/l of dissolved oxygen.
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The lungfish must have access to the water's surface. Lungfish gulp air into a primitive "lung" for
respiration
 Mouth is at the anterior end with jaws that can move freely.
 Highly maneuverable fins.
 Contain a swim bladder = a gas filled sac just above the stomach. Adjusts it’s buoyancy to keep from sinking or
rising. Helps compensate for a heavy bony skeleton.
 The Operculum (a flap of bony plates and tissue) covers and protects the gills.
 Lateral Line which senses movement in the water
 Have cycloid or ctenoid scales
Fish Anatomy
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anal fin - the fin on the lower side of the body near the tail…plays an important role in stability and balance.
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caudal fin - the tail fin. The main source of movement for most fish. It's like the motor on a boat.
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Fish with tails that are rounded or truncated are
usually slow swimmers, but these tails are
powerful so that these fish can swim far and
long.
 Fish with lunate tail shapes (pointed but not
sharply forked) are some of the fastest fish and
can maintain rapid speeds for long durations.
This would be very helpful for out-running
larger predators!
 Fish that are continuous swimmers usually have
a forked caudal fin, and the more active the fish
is, the deeper the fork tends to be.
dorsal fin - the fin on the upper side of the body…used in balance and steering for the fish.
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eye - sight organs located on the head.
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gills - fleshy organs that are used for breathing - they are located on the side of the head.
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lateral line - a series of sensory pores (small openings) that are located along the sides of fish - they sense vibrations in
the water.
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mouth - the part of the body which the fish uses to catch food - it is located at the front of the body.
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pectoral fin - each of the paired fins on either side of the body, near the head…they help in balance, swimming, and
turning.
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pelvic fin - each of the paired fins on the lower side of the body, near the head…important for stability.