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BIOLOGY 2201
UNIT II: Part B
Biodiversity
A Brief Survey of Animals
Textbook Reference: Sections 6.1 and 6.3
The study of animals is referred to as zoology. Animals are the largest of the five kingdoms and exhibit
the greatest diversity in terms of form and function. The general animal characteristics are as follows:
1.
2.
3.
4.
5.
Multicellular, eukaryotic organisms, with a division of labor amongst cells that are specialized.
A variety of systems have evolved and are specialized for specific functions. These may systems
include:
 Integumentary
 Reproductive
 Excretory
 Digestive
 Circulatory
 Endocrine
 Respiratory
 Lymphatic
 Nervous
 Muscular
 Skeletal
Lower forms of animals will not have complex systems.
Heterotrophic: Animals have more complex systems than plants. These systems are based
upon the animal’s nutrient requirements.
Locomotion: Most are mobile at some point in their lifetime
Reproduction: This may be through asexual or sexual means. Asexual reproduction will occur in
lower forms such as cnidarians which may reproduce through budding. Sexual reproduction will
occur in higher forms and may internal or external fertilization and development.
Five Major Areas Used to Describe Animals
1.
Systems: When moving form simpler to more complex animals 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 either be:
Incomplete: Two way system, having only one opening to the gut. Both food and wastes enter
and exit the same opening.
Complete: One way system, having two openings to the gut. Food enters one way, exits the
other.
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:
a. Asymmetric: Irregular shape and absence of balance. An organism can not be cut into
two matching halves. Ex: sponges, amoebas
b. Spherical Symmetry: Organisms are found in the shape of a sphere. Any cut through the
centre will divide it into two equal halves. Ex: protists like radiolarian
c. Radial: Any line cutting through the central axis of an organism from top to bottom or
front to rear. This cut divides it in half around a central axis in many ways but only the
one direction. For example, a hydra has mouth and tentacles at one end and is rounded
at the other. A jellyfish is another example. These organisms are not well adapted for
movement.
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BIOLOGY 2201
UNIT II: Part B
Biodiversity
d. Bilateral: This is an elongated body plan. There is only one line that divides the body in
half. This line runs down the middle of the longitudinal section. Each half is the mirror
image of the other. This is the most common form of symmetry. Ex: humans, frog
Assymetrical:
Spherical
Radial:
Bilateral:
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 (cephalization).
3.
Coelom: A coelom is a body cavity that has arisen from the mesoderm (see cell layers). 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 peritoneum lines
body cavities and covers internal organs. It may provide support and hold internal organs in
place.
Body cavities are important for the following reasons:
(i)
(ii)
(iii)
They provide space in which internal organs can be suspended so they are not
negatively affected by muscle pressure or body movement
They provide space for internal organs to develop and expand
They contain fluids which may assist in internal transportation and nutrient and gas
exchange.
Lower animal forms have no coelom or partial coeloms. They are acoelomates (cnidaria to
platyhelminthes). They are at a disadvantage in light of efficient functioning of a true coelom.
Organisms with a true coelom and are called coelomates.
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BIOLOGY 2201
UNIT II: Part B
Biodiversity
4.
Cell Layers: Germ layers refer to the number of cell layers early in the embryological
development of animals. In early stages of development, the embryo looks like a ball of cells
which begin to differentiate into 2 or 3 layers of cells. These layers independently differentiate
into various tissues of the animal body.
Animals contain either two or three embryonic cell layers. Simpler animals will contain only two
(Poriferans & Cnidarians). All others will have three. Each layer is responsible for producing
various tissues and structures in the adult animal. These layers include:
Ectoderm: These cells form the skin and the nervous system
Mesoderm: These cells give rise to organs of the circulatory, reproductive, urinary, skeletal and
muscular systems. The mesoderm gives rise to the coelom.
Endoderm: These cells form the lungs, liver, pancreas, and the lining of the gut or digestive tract
Diagram for Cell Layers:
5.
Reproduction: Moving from the simpler to more complex animal forms, the reproductive system
becomes more complex.
Animals have the ability to reproduce sexually and asexually. Several invertebrate classes have
the ability to reproduce asexually, whereas ALL vertebrates reproduce sexually
o Sexual reproduction involves both sperm and egg, with fertilization and development
occurring either inside the bodies of the parents (internal) or outside the bodies of the
parents (external)
o Asexual reproduction involves only parent, an example includes budding in which new
organisms grow from an outgrowth of their parent - some Poriferans & Cnidarians “bud”.
Animal Classification
There are two major groups of animals. They are classified according to the presence or absence of a
backbone.
1. Invertebrates
 Lacking a backbone
 Roughly 97% of the animal kingdom
2. Vertebrates
 Having a backbone
 Roughly 3% of the animal kingdom
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BIOLOGY 2201
UNIT II: Part B
Biodiversity
Invertebrates Characteristics
Textbook Reference: Section 6.3
1. These organisms lack a backbone.
2. Invertebrates include the following phyla:
 Porifera
 Annelida
 Coelenterata or Cnidarians
 Mollusca
 Platyhelminthes (flatworms)
 Arthropoda
 Nematoda (roundworms)
 Echindermata
3. Make up 97% of the animal kingdom
4. Higher forms are characterized by cephalization. Cephalization is an evolutionary tendency
towards specialization of the body with concentration of sensory and neural organs in the
anterior end (such as a brain). This reinforces the idea that animal body plans have evolved in
such a way that their organization is better equipped to find food
5. Possess body plans that have been enormously successful both ecologically and evolutionarily.
Phylum Porifera
- Means “pore bearing”
- Includes Sponges
- Are asymmetrical aquatic organisms with no coelom and only two cell layers.
- They have one body opening that allows 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
o Asexually via “Budding”
o Sexually via hermaphrodites (possess both male a female sex organs). Fertilization in
this case is external.
- They do not possess any sensory organs nor do they possess a nervous system.
- Their circulatory, excretory, and respiratory systems occur via diffusion
Phylum Cnidaria
- Means “thistle”, referring to stinging tentacles
- Includes Hydras, Sea Anemones, Jellyfish, and Coral
- They are radially symmetrical aquatic organisms made of two cell layers and therefore no
coelom.
- They have one body opening through which food enters and wastes leave, and unlike
Poriferans, they do have a digestive system, thus making it incomplete. Food is digested
extracellularly
- Reproduction is (1) asexually (budding) and (2) sexually, where organisms will have separate
sexes or will be (3) hermaphrodites. Fertilization is external
- Their circulatory, excretory, and respiratory systems occur via diffusion
- They have a simple nervous system known as a nerve net
Phylum Platyhelminthes
- Means “flat wide worm”, therefore they are commonly called Flatworms
- Includes Planarians, Flukes, and Tapeworms
- They are bilaterally symmetrical organisms and made of three germ layers with a true coelom.
- Can be either aquatic, terrestrial, or parasitic (living inside and feeding off other organisms)
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BIOLOGY 2201
UNIT II: Part B
Biodiversity
-
-
They have only one body opening through which food enters and wastes leaves. The digestive
system is known to be incomplete. Food is digested extracellularly.
They reproduce (1) asexually through regeneration, (2) sexually with species having either
opposite sexes and (3) in some cases hermaphroditic. Fertilization is internal
Their nervous systems are simple, comprising of a primitive brain and nerve cords. Sensory
organs are also very limited, with some species having only eye spots - a sensory organ
capable of detecting light from the 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 out of organisms).
Phylum Nematoda
- Means “thread like”, commonly called roundworms
- Includes Pinworms and Hookworms
- They are bilaterally symmetrical organisms and made of three germ layers with a true coelom.
- Can be either aquatic, terrestrial, or parasitic
- They have two body openings, therefore they have a complete one way digestive system where
food enters one opening and waste leaves the either. Food is digested extracellularly
- They reproduce sexually with species having either separate sexes or in some cases species
can be hermaphroditic. Fertilization is internal
- Like platyhelminthes, their nervous systems 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
- They are bilaterally symmetrical organisms and made of three germ layers with a true coelom.
- Can be either terrestrial or aquatic.
- They have two body openings, a one way complete digestive system. Food is digested
extracellularly.
- They reproduce sexually with species being of either separate sexes or hermaphrodites.
Fertilization is internal
- Fairly simple nervous system made of a primitive brain, some nerves, and ganglia (a mass of
nerve cells that give rise to a nerve center). There are added neural attachments heightens their
sensory capabilities, species are able to touch, taste, and sense light and moisture.
- Annelids have a closed circulatory system, meaning that at all times their blood is contained
within vessels.
- Like previous phyla, their respiratory system occurs primarily via diffusion but through the skin
into the blood.
- Their excretory systems are controlled by organs known as nephridia which are similar to flame
cells. Nephridia function like kidneys by filtering body fluids and pass wastes through to the
organisms exterior.
Phylum Mollusca
- Means “soft bodied”
- Includes Clam, Oysters, Octopus, and Snails
- They are bilaterally symmetrical organisms, made of three germ layers, and true coelom.
- Mainly aquatic but few do live on land  i.e. snails
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BIOLOGY 2201
UNIT II: Part B
Biodiversity
-
-
They have two body openings, a one way complete digestive system. Food is digested
extracellularly.
They reproduce sexually with species being of either separate sexes or hermaphrodites.
Fertilization is primarily internal however some species to display external fertilization.
Like Annelids, their nervous systems are slightly more developed than previous phyla. They
have a primitive brain and a few nerves with ganglia. Likeike Annelids, their sensory abilities are
heightened. They can sense touch, taste, smell, and in some species vision is possible 
Octopus.
Molluscs have an open circulatory system, their blood is not contained within vessels and
therefore has the ability to “slosh” around
Because many species are aquatic 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
- Means “jointed foot”. Arthropods have jointed appendages and hard exoskeleton
- Includes Insects, Crustaceans, and Centipedes
- They are bilaterally symmetrical organisms, made of three germ layers, true coelom.
- Are aquatic, terrestrial, and air borne.
- They have two body openings and one way complete digestive system. Food is digested
extracellularly.
- They reproduce sexually with species being either of separate sexes or some being
hermaphrodites. Fertilization is internal.
- Their nervous systems are advanced compared to other invertebrates with more advanced
brain, ventral nerve cord and ganglia. Their sensory abilities are also advanced. Many have the
ability to hear, taste, smell, touch, and see.
- They have an open circulatory system
- 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
o Malpighian tubules are a tubule network that collects liquid wastes and sends them to
the hind gut in the form of nitrogenous wastes. Found in insects.
o Green glands collect and excrete urine like kidneys. Found in crustacean like the
crayfish
Phylum Echinodermata
- Means “spiny-skinned”
- Includes Starfish, Sea Urchins, and Sea Cucumbers
- They are radially symmetrical organisms, made of three germ layers, true coelom
- Solely aquatic.
- They have two body openings, a one way complete digestive system, and food is digested
extracellularly.
- They reproduce asexually via regeneration and sexual reproduction is only possible through
separate sexes. There are no hermaphrodites. Fertilization is external.
- Their nervous system is relatively simple, comprising an oral ring and radial nerve cords.
Sensory abilities limited to simple touch and eye spots in some species
- They have a open circulatory system, and their respiratory systems utilize gills and diffusion
through the skin
- Excretory system made possible by diffusion
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BIOLOGY 2201
UNIT II: Part B
Biodiversity
Why are Arthropods so Successful?
Arthropods are the most biologically successful and abundant animal group on earth. There are more
arthropod species than all other species combined. There are 1 million known species. General
characteristics that enable success include:
1.
Symmetry is bilateral.
2.
Small coelom
3.
Jointed appendages for efficient locomotion.
4.
Exoskeleton that provides:
 Protection of internal organs
 Waterproof coating allowing many to live on dry land
5.
Segmented body with parts modified and fused to form specific body regions
(i)
Head – Anterior
(ii)
Thorax – Middle
(iii)
Abdomen – Posterior
6.
Posses a variety of well developed systems;
 Digestive
 Reproductive
 Respiratory
 Skeletal
 Excretory (green glands and
 Circulatory( open system)
malpighian tubules)
 Nervous system that is 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
The most successful class is class Insecta with 900,000 known species.
 Nearly all are terrestrial with a few freshwater and salt water forms
 Size range is broad from 0.25 mm for some species of beetles and up to 30 cm for some
tropical moths
The success of insects is credited to the following reasons:
(i)
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.
(ii)
There is tremendous variation in how they are adapted for feeding and reproduction. This
allows insects to exist in all kinds of environments and to obtain nourishment from many
sources
(iii)
High rate of reproduction and short life cycle. This increases the ability of insects to adapt.
(iv)
Small in size. This means that they do need large areas to live.
(v)
Adaptations to escape predators
(vi)
Social Insects
(vii)
Variations in body form
Some reasons for the success of arthropods/insects are discussed in more detail below:
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
expands, they are forced to periodically shed their exoskeletons. This process is known as molting.
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BIOLOGY 2201
UNIT II: Part B
Biodiversity
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, feeding, and locomotion. [Sensory
reception (Antennae), Eating (Mouth Parts), Locomotion (Legs, Swimmerets, Wings)]
Arthropods 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 feed on blood. Mouth parts have also evolved to cope with feeding difficulties such as
larger and stronger mandibles, fangs, teeth
Modified Mouthparts
Sucking Mouthparts
o Form a tube that can pierce tissues of plants and animals
o i.e. Mosquitoes/Butterflies
o Mandibles, maxillae, and parts of the pharynx are fused into a needle like structure
Sponging & Lapping Mouthparts
o Labium has a modification at its apex
o i.e. Fruit and House Flies
o Have a pair of soft lobes that serve as food channels
o Lap up food or liquefy with salivary secretions
Chewing Mouthparts
o Mouthparts adapted for seizing, grasping, & crushing food
o Adaptations for herbivores and carnivores
o Strong mandibles, toothed plates
o Enzymes are secreted form salivary glands that by way of chemical actions can liquefy food to
aid in the chewing process
Reproduction
o
o
Despite short life span they reproduce in extremely large numbers. They’ve also adapted
various techniques to attract mates including the use of pheromones (Enticing odours)
Some also have the ability to produce unfertilized eggs that are capable of growing into adults, a
process known as Parthenogenesis
Appearance
Many Arthropods have adapted appearance strategies with an advantage for protection or in some
cases attraction
o Camouflage: Organisms blend in with the environment so it cannot be easily seen
o Coloration: Organisms seeking to attract or repel prey, warning coloration signalling toxicity
o Mimicry: Insects adapt to look like another dangerous or poisonous insect
Developed Nervous System
o Arthropods have larger brains than nearest Invertebrate relative (Annelids). Many have the
ability to see, hear, taste, smell, and touch
o They also have a greater range of responsibility such as social Interactions and behaviour. For
example, ants & bees demonstrate a hierarchical social lifestyle required for their survival.
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BIOLOGY 2201
UNIT II: Part B
Biodiversity
Social Behaviour of Bees
o “Societies” display caste differentiation; there is a clear cut division of labour
o In such communities, all stages of their life cycles are present (i.e. Larvae, Pupae, and Adults)
o Activities within these communities are collective, each individual works to benefit the
community, they communicate with one another
o Social Castes of Bees
 Queen  single sexually mature female
 Drone  sexually mature males that mate with the queen
 Workers  Sexually inactive females that care to the colony; they feed young,
gather food, and care to the hive
o Castes are determined by fertilization and by what larvae are fed
o Drones develop parthenogenetically - From unfertilized eggs, they are haploid
o Queens and workers develop from fertilized eggs, they are dipolid
o Queens are fed a royal jelly produced by workers. Jelly contains enzymes that allow queen to
mature sexually
Questions (Use notes ot textbook)
1.
What are three examples of modified mouthparts in insects? How do these modifications work?
2.
Give examples of insects that use each of the following adaptations:
 Camouflage
3.

Warning coloration

Mimicry
Describe each of the following reproductive adaptations:
 Pheromones

Parthenogenesis
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BIOLOGY 2201
UNIT II: Part B
Biodiversity
4.
Why are insects so successful at reproduction?
5.
What is meant by a society of insects? What are some jobs of social insects?
6.
Describe how honeybees are social insects.
7.
Describe some of the variation in body form of insects.
8.
Describe how the legs of insects can be modified for specific functions.
9.
Distinguish between complete and incomplete metamorphosis. Provide examples for each.
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