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A Brief Survey of Animals
Animalia
The study of animals is referred to as
zoology.
Animals are the largest of the 6
kingdoms, and exhibit a great diversity
in form and function.
Major Animal Characteristics
1. Multicellular, eukaryotic organisms, with a
division of labour amongst cells that are
specialized.
 2. A variety of systems have evolved and are
specialized for specific functions. These systems
include:
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- Integumentary (skin)
- Digestive
- Respiratory
- Muscular
- Reproductive
- Circulatory
- Lymphatic
- Skeletal
- Excretory
- Endocrine
- Nervous
3. Heterotrophic: Animals have more
complex systems than plants. These systems
are based upon the animal’s nutrient
requirements.
4. Locomotion: Most are mobile at some point
in their lifetime.
5. Reproduction: This may be through sexual
or asexual means. Asexual occurs in some
lower forms, sexual occurs in all higher forms.
Five Major Areas Used to Describe Animals
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1. Systems: When moving from simpler to more complex
animal forms, the number and complexity of systems increases.
In the case of digestion, all animals except Poriferans digest
food extracellularly, meaning outside of their cells. Poriferans
digest food intracellularly, within their cells. Animal digestive
systems can be either :
Incomplete: two way system. Having only one
opening to the gut. Both food and waste
enter and exit the same opening.
Complete:
one way system, having two openings to
the gut. Food enters one way, exits the
other.
Intracellular digestion
Extracellular digestion
2. Symmetry: This is a term used to
describe the body plan of an animal. To find
the symmetry of an animal, an imaginary
line is drawn to divide the animal in half.
 There are three forms of symmetry:
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(A) Asymmetric - An organism cannot be cut
into two matching halves. (e.g. sponges)
(B) Radial - Any line passing through the
central axis of an organism divides it in half.
These organisms are rounded. (e.g jellyfish)
(C) Bilateral: An elongated body plan. There
is only one line that divides the animal in half.
This line runs down the middle of the
longitudinal section. This is the most common
form of symmetry. (e.g. humans, frogs, etc.)
Body Symmetry
When an animal has bilateral symmetry, the
body can be divided into 5 regions:
• Anterior: head region
• Posterior: rear region
• Dorsal: back region
• Ventral: bottom region
• Lateral: side region
The body symmetry of all animals is related to
the necessity of them to move in order to obtain
food. This is why most sensory organs are located
at the anterior end of the animal.
3. Coelom
A coelom is a body cavity. The presence or absence
of a fluid-filled cavity is one of the most significant
features of animal body plans used in classification.
 The coelom is located between the digestive tract
and the body wall.
 The peritoneum is associated with organisms which
have a true coelom. The peritonem lines body cavities
and covers internal organs. It may provide support and
hold internal organs in place.
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Body cavities are important for the following reasons:
(i) They provide space in which internal organs
can be suspended so they are not negatively
affected by muscle pressure and body movement.
 (ii) They provide space for internal organs to
develop and expand.
 (iii) They contain fluids which may assist in
internal transportation and nutrient and gas
exchange.
 Lower animal forms have no or partial coeloms.
They are at a disadvantage in light of the efficient
functioning of a true coelom.
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Development of coelum
4. Cell Layers: Animals contain either two or three
embryonic cell layers. Simpler
animals contain only two; all others have
three. Each layer is responsible for
producing various tissues and structures in
the adult animal. These layers include:
• Ectoderm - forms the outer body (skin, nerves)
• Mesoderm - forms the middle organs (kidney,
heart, urinary, skeletal and muscular)
• Endoderm - form lining of gut or digestive tract,
lungs,liver,pancreas
• simple animals have no mesoderm.
Germ layers
5. Reproduction: Moving from simpler to
more complex animal forms, the
reproductive system becomes more
complex.
Animals have the ability to reproduce
sexually and asexually. Several
invertebrates classes have the ability to
reproduce asexually, whereas all
vertebrates reproduce sexually.
Reproduction
Classification
There are two major groups of animals.
They are classified according to the
presence or absence of a backbone.
 Invertebrates
lacking a backbone
Roughly 97% of the animal kingdom
• Vertebrates
Having backbone
Roughly 3% of the animal kingdom
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Invertebrates
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1. These organisms lack a backbone, and
include the following phyla:
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(a) Porifera (sponge)
(b) Coelenterata (jellyfish)
(c) Platyhelminthes (tapeworm)
(d) Nematoda (ringworm)
(e) Annelida (earthworm)
(f) Mollusca (shellfish)
(g) Arthropoda (insects)
(h) Echinodermata (starfish)
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2. Make up 97% of the animal kingdom.
3. Higher forms are characterized by
cephalization. This is an evolutionary
tendency towards specialization of the body
with concentration of sensory and neural
organs in the anterior end( such as the brain).
4. They possess body plans which have been
enormously successful both ecologically and
evolutionarily.
Key Terms / Definitions Used in Animal
Classification
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Pseudocoelom - partial, not a true body cavity
2-way Digestive System - only one opening through
which food enters and undigested food exits
1-way Digestive System - two openings. Food enters
through the mouth and undigested food exits the anus.
One way system is better because it allows the animal to eat
continuously.
Diffusion - a substance goes from an area of high to low
concentration without any expenditure of energy
Open Circulatory System - blood is not always inside
blood vessels, and is not under pressure. It is slow and
inefficient, and does not transport oxygen.
Key Terms / Definitions (continued)
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Closed Circulatory System - blood is always inside
blood vessels, and is under pressure. It is fast, efficient
and transports oxygen.
Ganglia - a mass of nerve cells that give rise to a nerve
center.
Eye Spot - sensory organ capable of detecting light
from dark, does not see images
Flame Cell - cells that contain cilia that push waste
from an organism.
Nephridia - a unit that filters body fluids to remove
waste so that the fluid may be recycled.
Key Terms / Definitions (continued)
Malpighian Tubules - tubules that collect liquid
wastes within an organism and dump them into
the hind gut of the organism
 Green Glands - structures in which wastes are
collected and become concentrated within an
organism
 Tracheals - tubes leading into the body of the
organism for the purpose of gas exchange
 Hermaphroditic - possessing both ovaries and
testes
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Phylum Porifera
Means pore bearing
 Includes sponges
 Are asymmetrical aquatic organisms made of two layers
 They have one body opening that allows for food to enter
and waste to pass, however they do not have a digestive
system. All of their food is digested intracellularly.
 Poriferans can reproduce asexually or sexually
Asexual via budding
Sexual via hermaphrodites( fertilization occurs
external)
 They do not possess any sensory organs nor do they possess
a nervous system
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Phylum Cnidaria
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Means thistle, referring to stinging tentacles
Includes Hydras, Sea Anemones, Jellyfish, and Coral
They are radially symmetrical, aquatic organisms made of two
layers
They have one body opening through which food enters and
waste leaves and unlike Poriferans, they have no digestive
system, thus making it incomplete.
food is digested extracellularly
They reproduce asexually (budding) and sexually where
organisms will either have opposite sexes or will be
hermaphrodites
fertlization is external
Their circulatory, excretory, and respiratory system occur via
diffusion
they have simple nervous system known as a nerve net
Phylum Platyhelminthes
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Means flat wide worm therefore refers to flatworms
Includes Planarians, Flukes and Tapeworms
They are bilaterally symmetrical organism made of 3 germ layers
that can be eitehr aquatic terrestrial or parasitic(living inside and
feeding off other organisms)
They have only one body opening through which food enters and
waste leaves. They do not have a digestive system thus because
there is only one opening, the digestive system is known as
incomplete
food is digested extracellularly
They reproduce asexually through regeneration or sexually with
species having opposite sexes or in some cases species can be
hermaphroditic
fertilization is internal
Their nervous system is simple , comprising of a
primitive brain and nerve cords. Sensory organs
are also very limited, with some species having
eye spots- a sensory organ capable of detecting
light from dark.
 Their circulatory and respiratory systems occur
via diffusion while their excretory systems are
accomplished via flame cells
◦ Flame cells are ciliated excretory cells found
in lower invertebrates that function like a
kidney to remove waste
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Phylum Nematoda
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Means thread like commonly called roundworms
Includes pinworms and hookworms
They are bilaterally symmetrical organisms, made of 3 germ
layers, that can be either aquatic, terrestrial or parasitic
They have 2 body openings, therefore have complete one way
digestive system
food is digested extracellularly
They reproduce sexually with species having either opposite sex
or in some cases species can be hermaphroditic
fertilization is internal
Like plathyelminthes, their nervous system are simple, made of a
primitive brain and nerve cords. Their sensory capabilities are
limited to touch.
Their circulatory and respiratory systems occur via diffusion and
their excretory system is controlled by flame cells
Phylum Annelida
Means ring referring to body being segmented into
repeating units
 Includes earthworms, leeches and tubeworms
 Bilateral symmetry, made of 3 germ layers, and are
aquatic or terrestrial
 Have 2 body openings, one way digestive n system and
tube-tube body plan
food is digested extracellularly
 Reproduce sexually with species of either opposite sex
or hermaphrodites
fertilization is internal
 Fairly simple nervous system made of primitive brain ,
some nerves and ganglia- a mass of nerve cell that give
rise to a nerve center
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The added neural attachments heightens their sensory
capabilities, species are able to touch taset and sense
light and moisture
Annelids have a closed circulatory system, ,meaning that
at all times their blood is contained within vessels
Respiratory system occurs via diffusion through the skin
Their excretory system are controlled by organs called
Nephridia
similar to flame cells nephrida function like kidneys, to
remove wastes out of body. They filter body fluids , the
pass wastes through to the organisms exterior.
Phylum Mollusca
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Means “soft bodied”
Includes Clam, Oysters, octopus, and snails
They are bilaterally symmetrical organism, made of 3 germ layers, that are
mainly aquatic, but few do live on land- ie. Snails
They have two body openings, a one way complete digestive system and a
tube within a tube body plan
Food is digested extracellularly
They reproduce sexually with species being of either opposite sexes or
hermaphrodites
fertilization is primarily internal however some species do display external
fertilization
Like annelids their nervous system is slightly more developed than previous
phyla. They have primitive brain, a few nerves with ganglia. And like Annelids
because of this their sensory abilities are heightened. They can sense touch
taste smell and in some species vision is possible (octopus).
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Have an open circulatory system, their blood is
contained within vessels and therefore has the ability to
slosh around
Many of they are aquatic and therefore they’ve adapted
gills for respiration while those few species that live on
land do have a very simple lung
Excretory system mainly controlled by nephridia
Phylum Arthropoda
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Means jointed foot, arthropods have jointed appendages and hard
exoskeleton
Includes insects, crustaceans, and centipedes
They are bilaterally symmetrical organisms , made of 3 germ layers
that re aquatic, terrestrial and air borne
They have two body openings and one way complete digestive
system
 Food is digested extracellualrly
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They reproduce sexually with species being either of opposite
sexes or some being hermaphrodites
Fertilization is internal
• Their nervous system are advanced compared to other
invertebrates with that in mind their sensory abilities are also
advanced. Many have the ability to hear taste smell touch and see
• They have open circulatory systems
• Have respiratory systems made of gills and tracheals. Tracheals
are tubule networks involved in gas exchange
• Excretory system made of malpighian tubules and green
glands
 Malpighian tubules: are a tubule network that collects
liquid wastes and sends them to
the hind gut in the form of
nitrogenous wastes
 Green glands:
collect and excrete urine
Phylum Echinodermata
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Means spiny skinned
Includes starfish, sea urchin and sea cucumber
They are radially symmetrical organism, made of 3 germ layers that
are solely aquatic.
They have two body openings, a one way digestive system and have
a tube –within- a tube body plan
 Food is digested exrtacellularly
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They reproduce sexually and asexually via regeneration, sexual
reproduction is only possible through opposite sexes, there are no
hermaphrodites
 Fertilization is external
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Their nervous system is relatively simple comprising an oral ring
and radial nerve cords
 Sensory abilities limited to touch and eye spots in some species
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They have an open circulatory system and their respiratory system
utilizes gills and diffusion through skin
Excretory system made possible by diffusion
Why are Arthropod so successful?
1. Most biologically successful and
abundant animal group on earth.
 2. There are more arthropod species
than all other species combined.
 3. There are 1 million known species.
 4. Symmetry is bilateral.
 5. Small coelom.
 6. Jointed appendages for efficient
locomotion.
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7. Exoskeleton that provides:
(a) protection of internal organs
(b) waterproof covering allowing many
to live on dry land
 8. Segmented body with parts modified
and fused to form specific body
regions:
(a) head – anterior
(b) thorax - middle
(c) abdomen - posterior
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9.Possess a variety of well developed systems:
a) Digestive
 b) Respiratory
 c) Excretory
 d) Reproductive
 e) Skeletal
 f) Circulatory - open system
 g) Nervous - well developed with the following
features:
(i) distinct brain
ii) ventral nerve cord
(iii) sense organs such as eyes, auditory
organs, sensory bristles, and antennae
that touch and sense chemicals
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Arthropod Exoskeleton
Arthropods have developed a rigid and
jointed external skeleton made of a
waterproof material known as chitin.
 The skeleton provides many advantages
including a site for muscle attachment and
protection of bodily tissues.
 Because Arthropods do grow and
because their exoskeletons cannot
expand they are forced to periodically
shed their exoskeletons. This is called
molting
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Arthropods: Specialized Body Segments
Arthropods have developed three body segments which are
often fused
 Head
 Thorax
 Abdomen
 Their appendages are attached to these regions providing them
with the ability to develop and specialized for specific functions
including sensory reception (antennae),feeding, (mouth
parts) and locomotion (Legs, swimmerets, wings).
 They have evolved in such a way that they`ve adapted to obtain
nourishment in a variety of ways, eating both plant and animal
tissues. Some may feed on either other insects of different
phyla or their own. Some may feed on blood. Mouth parts
have also evolved to cope with feeding difficulties such as larger
and stronger mandibles fangs and teeth.
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Modified Mouth parts
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Sucking Mouthparts
Form a tube that can pierce tissues of plants and animals
ex. Mosquitos butterflies
Madibles, maxillae, and other parts of the pharynx are fused into a needle
like structure
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Sponging and lapping mouthparts
Labium has a modification at its apex
Ex. fruit and house flies
Have a pair of soft lobes that serve as food channels
lap up food or liquefy with salivary secretions
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Chewing mouthparts
Mouthparts adapted for seizing, grasping, and crushing food
Adaptations for herbivores and carnivores¸ strong mandibies, toothed
plates
Enzymes are secreted from salivary glands that by way of chemical actions
can liquefy food to aid in the chewing process
Reproduction
Despite short life spans they reproduce in
extremely large numbers. They` ve also adapted
various techniques to attract mates including
the use Pheromones (enticing odours)
 Some also have the ability to produce
unfertilized eggs that are capable of growing
into adults, a process known as
Parthenogenesis
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Appearance
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Many have adapted appearance strategies with
an advantage for protection or in some cases
attraction
Camouflage: organisms blend in with the environment
so it cannot be easily seen
Coloration: organisms seeking to attract or repel
prey, warning coloration signalling toxicity
Mimicry: insects adapt to look like another dangerous
or poisonous insect
Developed Nervous System
Have a larger brain than nearest
invertebrate relative (Annelid). May have
the ability to see, hear, taste, smell and
touch
 Have a greater range of responsibility
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Social interactions and behaviours
Ants and bees demonstrate a hierarchical social
lifestyle, one is required for their survival
Social Behaviour of bees
Societies display as caste differentiation there is a clear division of
labour
 All stages of life are present(larvae, pupa, adults)
 Activities are collective, each individual works to benefit the
community.
 social castes of bees
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Queen: single sexually mature female
Drone: sexually mature males that mate with the queen
Workers: sexually inactive females that cars for the colony, feed young
gather food and care for the hive
Casts are determined by fertilization and by what larvae are feed
 Drones develop parthenogenetically from unfertilized eggs and
are haploid
 queens and workers develop from fertilised eggs they are diploid
 Queens are fed royal jelly produced by workers which contains
enzymes that allow queen to sexually mature
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The most successful class is class Insecta with 900,000
known species
Nearly all are terrestrial with a few fresh
 Size range is broad; from 0.25 mm for
some species of beetles and up to 30 cm
for some tropical moths water and
saltwater forms
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The success of insects is credited to the
following reasons:
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(1) They are the only invertebrates capable of flying.
This allows them to move over great distances to find
food, escape predators, and spread to new
environments.
(2) There is tremendous variation in how they are
adapted for feeding and reproduction, so they can exist
in all kinds of environments and obtain nourishment
from many sources.
(3) High rate of reproduction and short life cycle. This
increases the ability of insects to adapt.
(4) Small in size. This means they don’t need large
areas to live.
(5) Social insects
(6) Variations in body form
Phylum Chordata
There are three basic characteristics that distinguish
phylum Chordata from all other animal phyla
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(1) The presence of a flexible, rod-like, internal
supporting structure called a notochord. It runs the
length of the organisms near the dorsal surface. In
vertebrates it is replaced during embryonic development by
cartilage or bone
 (2) The presence of a hollow dorsal nerve cord. This
lies just above the notochord. This tube will eventually
form the brain and spinal cord of the adult.
 (3) Gill slits are present at some time in development.
These are paired openings in the wall of the pharynx. In
some vertebrates, gill slits are only seen in the embryo.
In others such as fish they are present and function
during respiration for life
Vertebrates
1. They are a subphylum under the Phylum
Chordata. This means they possess a
dorsal nerve cord, notochord, and gill slits
at the embryo stage.
 2. Vertebrates are the most numerous
(95%) and most complex of all chordates.
 3. Possess a backbone. The vertebrae
surround and protect the nerve chord.
Vertebrae develop from and replaces the
notochord.
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4.Anterior part of the dorsal, hollow
nerve cord is enlarged into a brain
(cephalization). The cerebrum has
increased in size and is more complex.
 5. The body is usually divided into head,
neck, and trunk. The head contains the
brain and various sense organs.
 6. A tail is present at some stage of
development.
 7. Jointed internal skeleton (endoskeleton).
 8. Two pairs of appendages.
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9. There is a ventral heart with two to four chambers.
The circulatory system is closed, and red blood cells
contain hemoglobin to bond to oxygen.
 10. In aquatic vertebrates, gas exchange takes place in
gills. In land vertebrates, it occurs in the lungs.
 11. Large coelom containing increasingly complex
organ systems.
 12. The body covering, the skin, is made up of at least
two layers: the epidermis and the dermis. The skin
often forms other structures such as glands, scales,
feathers, hair, nails, claws, horns and hoofs.
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VERTEBRATES
FISH
Group includes 7 classes:
• agnatha
(jawless)
• chondrichthyes (cartilaginous)
• osteichthyes
(bony)
• amphibia
(e.g. frog)
• reptilia
(e.g. alligator)
• aves
(e.g. eagle)
• mammalia
(e.g. human)
Fish are the most numerous and
widespread of all vertebrates.
 59% salt water
 40% freshwater
 1% move regularly between salt and fresh
water
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Vertebrate Respiration
 Fish are the only vertebrate adapted to live
their lives solely in water
Water is source of oxygen for cellular respirtion
Obtain oxygen from water by way of gills
Water travels over and through gills allowing oxygen and
carbon dioxide to be exchanged between the water
outside their bodies and their blood inside. Counter
current exchange
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Reptiles, Birds, and mammals
Have lung based respiratory systems used to obtain
oxygen from air
Functional units of lungs are known as alveoli
their main function in the lung is to transport oxygen
into the blood stream and remove carbon dioxide
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Amphibians
Utilise lungs and their skin to carry out gas
exchange
However because their lives commence in
water they also utilize gills
Vertebrate Circulation
There are 3 types of Circulatory Pathways
 Fish
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Blood flows through a two chambered heart in a one
way circuit pathway
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Amphibians and most reptiles
Blood flows through a three chambered heart into a
two circuit pathway
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Crocodiles, birds and mammals
Blood flows through a four chambered heart that is
completely separated into right and left halves.
Right half pumps blood to the lungs (deoxygenated)
Left pumps blood to the rest of body (oxygenated)
Vertebrate Reproduction
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External
Sperm and egg meet outside the bodies of the parents
Fish and frogs
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Internal
Sperm and egg meet inside the bodies of the parents
Reptiles birds and mammals
Reptiles and birds lay eggs
Mammals are the only vertebrate where embryo
development occurs internally
Some exceptions duckbill platypus and marsupials
Vertebrate Classes
Class Agnatha
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Jawless fish that are smooth and shiny
Approx. 60 species of lampreys and hagfish
Tube shaped, 1 metre long
Have an endoskeleton made of cartilage
Complete digestive system
scavengers and parasites
Hagfish bore holes in dead and dying fish
lampreys often latch on to other fish with their sucker like mouths
respiratory system made of 6-14 Pairs of gills
lack an opercuclum
have a circulatory system composed of a two chambered heart
Nervous system composed of a small brain, 8-10 pairs of cranial nerves and a
spinal cord with spinal nerves
reproduce sexually with externally fertilization
Ectothermic
Excretory system composed of 2 kidneys, 2 ureters, a bladder and a urinary
opening
Class Chondrichthyes
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Cartilaginous fish
Approx. 850 species
Includes sharks, rays and skates
Have scales and a skeleton of cartilage not bone. Flexible
Respiratory system made of 5-7 pairs of gills
Lack an operculum
Complete digestive system
Reproduce sexually with primarily internal fertilization no parental
care
Nervous system composed of small brain, 8-10 pairs of cranial
nerves, a spinal cord with spinal nerves
Ectothermic
Excretory system composed of 2 kidneys, 2 ureters, a bladder and
a urinary opening
Class Osteichthyes
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Bony fish
Most numerous of all vertebrates
 Approx 20000 species
 Includes trout and herring
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Have skeleton made of bone and a complete digestive system
Have a swim bladder which is an internal organ used fro buoyancy
All have a lateral line
 Sense organ that is sensitive to pressure change in the water and can detect nearby
movement
 Detects vibrations and movements to detect predators and prey
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Respiratory system made of gills which are covered by an opercuclum
have a two chambered heart
Reproduce sexually with external fertilization and external development
Ectothermic
Nervous system composed of a small brain, 8-10 Pairs of cranial nerves
and a spinal cord with spinal nerves
Excretory system made of 2 kidneys, 2 ureters, a bladder and urinary
opening
Class Amphibia
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Includes approx 4000 species of frogs toads newts and
salamanders
Undergo metamorphosis
Change in life stages
Larval stage begin life in water and breathe using gills. Adult stage live
life on land and use lungs and skin for respiration
Three chambered heart with little blood mixing
 Complete digestive system and a nervous system slightly
more developed than that of fish
 Reproduce sexually with fertilization and development
occurring externally
 Ectothermic
 Excretory systems made of 2 kidneys, 2 ureters, a bladder, and
a cloaca
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A common opening for the release of urine and feces
Class Reptilia
Approx 4000 species including snakes, alligators, crocodiles, and
turtles
 Have skin made of keratin which is impermeable to water
 Endoskeleton made of bone and cartilage, use lungs to breathe
 3 chambered heart and a complete digestive system
 Nervous system that is more developed than latter classes of
vertebrates
 Ectothermic, Excretory system lacks a bladder
 Reproduce sexually with fertilization occurring internally while
development occurs externally
 Reptiles lay eggs that contain 4 vital membranes which aid in
development
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Chorion
Amnion
Yolk sac
allantois
Class Aves
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Approx 9000 species of birds
Three types of feathers
Down: insulation
Contour: Shape and color
Quill: Flight
Structurally adapted for flight have hallow bones that are equipped with air sacs.
Air passes through lungs and air sacs so oxygen ne extracted
Complete digestive system
Circulatory system controlled by a 4 chambered heart with a septum
Blood does not mix
Reproduction is sexual with fertilization occurring internally and development
externally
Lay eggs the egg white is an extra protein source for the embryo
Endothermic,
Slightly more developed nervous system and have excretory systems similar to
reptiles
Class Mammalia
Includes humans, monkeys , whales
 Have hair and mammary glands
 Endoskeleton made of bone and cartilage
 Utilize lungs to breathe, obtain oxygen from air
 Most developed of all vertebrates
 Circulatory system controlled by 4 chambered heart with a septum
 endothermic
 Excretory system made of 2 kidneys, 2 ureters, bladder and a
urethra
 Reproduction is sexual with fertilization internal and development
occurring both internally and externally
 Three types of mammals
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 Monotremes: lay eggs and incubate like birds (platypus, anteater)
 Marsupials: pouched mammals with partial external development and nourished
externally (kangaroos , opossums)
 Placentals: Placentae and umbilical cord for internal development