Fundamentals of Biology
Lesson 21
Chordates, Vertebrates, and Fish
I. Phyla, Subphyla.
A. Hemichordata.
B. Chordata.
1. Urochordata.
2. Cephalochordata.
3. Vertebrata.
II. Hemichordata - acorn worms.
A. Invertebrates; formerly classed as chordates.
1. Possess pharyngeal gill slits
(compare with pharyngeal pouches in chordates).
2. Once thought to have a notochord.
B. General Characteristics.
1. All are marine.
2. Some are burrowing worms
3. Others are sessile with tentacles.
4. Three part body.
a. Proboscis
- ciliated; used for burrowing and feeding.
b. Collar -
mouth.
c. Trunk -
digestive tract.
5. Both ventral and dorsal nerve
cords.
III. Chordata.
A. General Characteristics.
1. Dorsal notochord at some
stage of life.
a. Tough,
flexible, rod-like structure running the length of the body.
b. Serves as
primary support.
2. Dorsal tubular nerve chord; brain
at anterior end.
3. Pharyngeal pouches at some
stage in life.
a. Folds of
skin along the neck region.
b. Aquatic
organisms: they open into gill slits.
c. Others: do
not open.
4. Ventral heart.
5. Endoskeleton.
6. Postanal tail at some stage in
life.
B. Urochordata - tunicates.
1. All are marine.
2. Only larva has notochord.
3. Ascidians are sessile, others are
planktonic.
4. Ascidians (sea squirts).
a. Secrete
cellulose covering.
b. Filter
feeders.
c. Many
colonial.
C. Cephalochordata - amphioxus (lancelets).
1. Marine.
2. Look like fish with too many gill
slits.
3. Bury all but head in sand.
4. Cilia pull food into mouth.
IV. Vertebrata.
A. General Characteristics.
1. Vertebral column: more or less
replaces the notochord.
2. Liver, endocrine organs, kidneys.
3. Prominent cephalization.
B. Terms.
1. Oviparous: eggs hatch
outside the body.
2. Viviparous: offspring are
nurtured in the mother’s body by a placenta.
3. Ovoviviparous: eggs hatch
inside the mother’s body, but there is no placenta.
4. Ectothermic (cold-blooded):
cannot generate their own body heat.
5. Endothermic (warm-blooded):
generate their own body heat.
C. Classes of Fish.
1. Agnatha (Jawless Fish).
2. Chondrichthyes (Cartilaginous
Fish).
3. Osteichthyes (Bony Fish).
V. Agnatha.
A. General Characteristics.
1. No jaws.
2. Long, narrow, cylindrical body.
3. No paired fins.
4. Cartilage skeleton.
B. Lampreys.
1. Temperate aquatic habitats.
2. Two dorsal fins and a tail fin.
3. Parasitic.
a. Sucking
mouth, rasping tongue covered with teeth.
b. Mouth
holds it to the host.
c. The tongue
breaks the skin.
d. It then
sucks the blood and body fluids of the host.
e. Usually
does not kill its prey.
4. Larval form lives as long as seven
years as an amphioxus-like filter feeder.
5. Adult lives only a few years; dies
after spawning upriver.
C. Hagfish.
1. Temperate and semitropical
Atlantic and Pacific habitats.
2. Eat dead, diseased, or disabled
fish as well as invertebrates.
3. Can bite using cartilage rods on
either side of the mouth.
4. No larval stage.
VI. Shared Characteristics of Chondrichthyes and Osteichthyes.
A. Jaws.
B. Two pairs of lateral fins.
1. Pectoral fins (front).
2. Pelvic fins (rear).
3. Permit a greater degree of balance
and maneuverability.
C. Unpaired dorsal, anal and tail fins.
VII. Chondrichthyes.
A. Sharks.
1. Covered with tiny scales.
2. Carnivorous.
a. Some are
filter feeders.
b. These feed
on plankton.
3. Digestive System.
a. Teeth are
enlarged, specialized scales.
b. Swallow
food whole – as much as a dolphin or part of a horse.
c. Digestion
mainly in the stomach.
d. Absorption
in the intestine.
e. Intestine
is short and fat, but surface are increased by a spiral valve.
4. Enormous liver.
a. Stores
lipids.
b. Lipid
content regulates buoyancy.
5. Respiratory System.
a. Lack
pumping muscles to draw a water current across the gills.
b. Thus they
need to swim constantly or they will drown.
6. Nervous System.
a. Large olfactory
organs in their heads to detect chemicals.
b. Lateral
line system.
i. Pressure receptors on the side of the body.
ii. Detect vibrations or sound waves.
c. Ampullae
of Lorenzini.
i. Specialized lateral line receptors in the head.
ii. Long mucus-filled canals.
iii. Detect electric fields.
7. Reproductive System.
a. Internal
fertilization.
b. Many
ovoviviparous, but some are viviparous and others are oviparous.
c. Females
produce a few large eggs with a lot of yolk.
d. Males use claspers,
extensions of the pelvic fins, to pass sperm to the females.
e. Eggs of
oviparous sharks are covered with leathery coat.
f. In most
species the eggs remain in the oviduct until the baby shark is ready to be born.
g. The sand
tiger embryos eat the other embryos and eggs coming from the ovary.
B. Rays and Skates.
1. Pectoral fins are enlarged into
wings that propel them through the water.
2. Stingrays have sharp, poisonous
spines that cause painful wounds.
3. Electric rays stun prey or enemies
with an electric shock.
4. Manta rays can get as large as 20
feet across.
VIII. Osteichthyes.
A. Covering.
1. Most have scales.
2. Mucus covers the scales.
a.
Waterproofs.
b. Protects
from parasites.
c. Lubricates
for swimming.
3. Chromatophores: branched
cells that produce pigments.
a.
Rearranging the pigment in the cell changes the color of the fish.
b. Color
changes in response to temperature, diet, excitement, physical condition.
c.
Countershading.
i. Dorsal side is dark to blend in with the dark deep water.
ii. Ventral side is light to blend in with the bright suface.
B. Movement.
1. Moves mainly by whipping motion of
its body.
2. Many have an air bladder, a
thin-walled sac containing gases to regulate buoyancy.
C. Digestive System: mouth, pharynx, esophagus, stomach,
intestine, anus.
D. Respiratory System.
1. Operculum: a plate behind
the eye on each side of the head.
2. Gills are underneath the
operculum.
a. Two rows
of thin gill filaments on a cartilage band called a gill arch.
b. Each
filament is a stack of thin plates.
c. These
plates are covered by a thin epithelium and filled with blood vessels.
3. Two-stage process of respiration.
a. Operculum
closes, gill arches expand drawing water into the mouth.
b. Mouth
closes, gill arches contract, operculum opens forcing water over the gills
4. O2 and CO2
are exchanged, up to 85% efficient.
E. Circulatory System.
1. Two-chambered heart.
2. Sinus venous empties into
the atrium.
3. Atrium pumps blood into the ventricle.
4. Ventricle pumps blood through the ventral
aorta.
5. Blood passes through the gills;
gives up CO2 and takes in O2.
6. Oxygenated blood enters the dorsal
aorta.
7. Blood passes through the body
tissues and returns to the sinus venous.
F. Nervous System.
1. Brain with major lobes; spinal
cord.
2. Smell.
a. One of
sharpest senses.
b. Olfactory
sacs behind the nose.
3. Lateral line system.
a. Pressure
receptors on the side of the body.
b. Detect
vibrations or sound waves.
4. Taste and touch on the tongue.
5. Sight.
F. Reproductive System.
1. Most are oviparous, but some are
ovoviviparous and some are viviparous.
2. Female
a. Paired
ovaries.
b. Can
produce 100,000's of eggs.
3. Female spawns.
4. Male covers the eggs with milt
– milky fluid containing sperm.
5. Few hours to 90 days for eggs to
hatch.
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