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Chordate Characteristics

Characteristics of Chordates

•A chordate is an animal that in some stage of development has:1.Notochord- dorsal rod of

specialized nerves2.A dorsal hollow nerve cord- tube

just above the notochord3.Pharyngeal pouches- small out

pockets of the anterior gut (may become gills in some animals)

4.Postanal Tail-a tail that extends beyond the anus 2

Characteristics Continued• Notochord exists only in the

embryo

• Notochord replaced by an endoskeleton

• In lower chordates (fishes amphibians) pharyngeal pouches evolved into gill slits

• In terrestrial vertebrates pharyngeal pouches evolved into structures in throat and ear

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ClassificationPhylum Chordata has 3 subphyla

1. Urochordata-Tunicates2. Cephalochordata-Lancelets3. Vertebrata

Subphylum Urochordata• Hollow barrel shaped

Urochordates are commonly called Tunicates and Sea Squirts

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Subphylum Cephalochordata

• Marine organism (usually shallow water)

• Best represented by a blade-shaped, animal called a

lancelet

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Subphylum Vertebrata•Brain protected by an outer skull

and spinal cord protected by vertebrae

•Organs of vertebrates are organized into 10 systems Skeletal, muscular, integumentary,

digestive, respiratory, circulatory, excretory, immune, nervous, and reproductive 6

Characteristics of All Vertebrates Bilateral symmetry Two pairs of jointed appendages

such as limbs or fins Cephalization with complex

brains and sense organs True coelom lined with

mesoderm Closed circulatory system-blood

in vessels and heart Chambered heart Either ectothermic (cold blooded)

or endothermic (warm blooded)7

Vertebrate Classes

Fish Amphibians Reptiles Birds Mammals

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Classes of Fish1.Agnatha-Jawless Fish2.Chondrichthyes-Sharks

Skates and Rays

3. Osteichthyes-bony fish• Fishes are the most

numerous of all vertebrates and most widespread in their distribution

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Adaptations of Fishes

Swimbladder-adaptation for buoyancy- traps gas inside their body: gas swim bladder is used to regulate their vertical position

Single Loop Blood Circulation-Blood goes to the gills, is oxygenated and sent to all parts of the body

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GillsMade of gill filaments where gases

enter and leave the blood (Oxygen and Carbon Dioxide)

Gill slit-opening at the rear of the cheek

Countercurrent flow - the water passing over the gills and the blood flow inside the gills is in the opposite directions-this increases the gill’s efficiency

Fish can extract 85 % of the oxygen passing over the gills 11

Circulation of Blood in Fish Single loop circulation

in fish

Atrium-chamber with thin, muscular walls

Ventricle-a thick walled pump with much force

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Excretory Organ-Kidneys

Kidneys are organs made up of thousands of nephrons

Nephrons are tubelike units that regulate salt and water balance and remove metabolic wastes from the blood

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Reproduction in Fish

Separate sexes in most fishes Usually external fertilization Yolk sac in egg contains

nutrients Large numbers of eggs are

fertilized during spawning Sharks, Skates and Rays

fertilization is internal-most are born live

Some sharks lay eggs14

Adaptations of Fishes

Scales limit chemical exchanges through the skin; exchanges occur through the membranes of the gills

Lateral line system consists of a row of sensory structures that run the length of the body and connected by nerves to the brain; detects vibrations

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Agnatha “jawless”

• Examples:Lampreys and hagfish live in the ocean

• Lampreys attach to fish-parasites

• No lateral line system• Have “round mouths”- no scales• Have Notochord, a cartilaginous skeleton, and unpaired fins

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Hagfish•Bottom dwellers in cold marine

waters

•Scavengers of dead and dying fish on ocean bottom

•When not feeding they remain hidden in burrows on the ocean floor

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Chondrichthyes CHONDRICHTHYES-SHARKES,

SKATES AND RAYS chrondros=cartilage ichthyes=fish movable jaws no swim bladder cartilage strengthened by calcium

carbonate or bone placoid scales Teeth-modified scales

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Sharks•Sharks are scavengers •The shark’s mouth has 6 to 20

rows of backward-pointing teeth•They can detect blood from an

injured animal as far as 500 miles away

•They swim with a side-to-side motion of their asymmetric tail fins.

•Gas exchange requires a continuous passage of water over a shark’s gills

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Osteichthyes Osteon=bone ichthyes=fish Skeletons rigid, calcium bases Movable jaws Gill cover or operculum Scales Most have swim bladders Most have separate sexes-

fertilization external20

Types of Osteichthyes or Bony Fish

1. The Lungfish resembles a short-bodied eel- Lungfishes have gills where gas exchange normally takes place

2. During dry periods they burrow unto the mud and cover themselves in mucus to stay moist until the pond refills

Their "lung" is a modified swim bladder, which also absorbs oxygen and removes wastes during this dry time

The various species are found in the lakes and rivers of South America, Africa and Australia

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Osteichthyes Continued

2. Lobe-finned fishes-have paddle like fins with fleshy bases.

3. Ray-finned fishes have fins that are supported by the long bones called rays-Most familiar fishes and include snake-like eels, salmon, trout, bass, herring, and lantern fish

(most fish we eat) 22

Morphology of a Bony Fish or Osteichthyes

External Anatomy1. Distinct head, trunk, and tail

regions2. Each side of head is operculum- Hard plate that opens at rear

and covers and protects gills1. Strong muscles along dorsal

backbone thrust tail from side to side

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Fin Characteristics

• Thin fan-shaped membranes• Richly supplied with blood• By raising and lowering fins,

regulate body temperature• Supported by rays or spines1. Rays- bony yet flexible2. Spines- bony and rigid

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Scales1. Skin covered with scales-

highly modified bone that grow from pockets of skin

2. Overlap like roof shingles, all pointing toward tail to minimize friction

3. Grow during entire life of fish4. Scales grow quickly when

food is abundant and slowly when scarce

5. Skin contains pigmented chromatophores-which

create various color patterns

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Circulatory System• Adapted for rapid swimming and

other high-performance activities • Consists of:

Two-chambered heart Atrium- collecting chambers Ventricle- pumping chambers Blood vessels Blood-red and white blood cells

• Heart pumps blood to arteries capillaries in gills blood picks up oxygen gas and releases carbon dioxide into water blood moves to body tissues, where nutrients and wastes are exchanged blood returns by veins to heart

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Respiratory and Excretory Systems Work Together• Gills adapted for gas exchange

• Each has double row of thin projections called gill filaments richly supplied with capillaries

• Large surface area allows rapid gas exchange

• Gills also excrete nitrogenous wastes from body, but task carried out primarily by kidneys

• Kidney’s filter out dissolved chemical wastes from blood

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