Body Symmetry
&
Coelomate

Symmetrical

Acoelomate
no mesoderm

Pseudocoelomate
mesoderm attach to one side but
no cleavage

Coelomate
mesoderm cleavage with coelom inbetween

Segmented Body

Porifera (spongy)
•Asymmetric body
•Lack of body
organizaiton

Structure
•Spicules as
structural
component
•Choanocyte
for water flow
and feeding

Adaptive features
Gaseous exchange diffusion
Nutrition Choanocyte filtering
Support water
Fertilization external
Embryo develop no
Movement no
Special features Asymmetical no mouth no anus

Introduction to
coelenterata
Radially symmetrical
Diploblastic
With nematocysts for food capture
and protection

No blood, respiratory, or excretory organs
A network of nerve cells and fibres exists
in body wall
Single internal cavity with only opening to
the exterior, the ‘mouth’ which is
surrounded by tentacles
Reproduction by assexual budding in polyp
stage, sexual reproduction by eggs and
sperm in medusa stage

Polyp and Medusa
• Polyp
• body is tubular or cylindrical
• oral end, bering the mouth and
tentacles, is directed upwards, and the
opposite, or aboral end is attached
• layer of mesoglea is thin

Polyp

 Medusa
 body resembles a bell or umbrella, with
the convex side upward and the mouth
located in the cneter of the concave
under-surface
 tentacles hang downwards from the
margin of the ‘bell’
 layer of mesoglea is extremely thick

Medusa

Adaptive features
Gaseous exchange diffusion
Nutrition Holozoic by nematocyst
Support water
Fertilization external
Embryo develop external
Movement Only in larva and medusa
Special features Nematocyst, polyp, medusa
Radial symmetrical, acoelomate

Nematoblasts
 Nematoblasts
1. they are in the ectoderm
2. each consists of highly complex
organelle, nematocyst, which is a
minute capsule filled with fluid and
containing a coiled, barbed thread tube

 when the triggering device, cnidocil, on
the outer surface of the nematoblast
is stimulated, the thread tube everts
to aid in capture of prey, protection or
locomotion

Morphology of Obelia
1. Classification
– Class Hydrozoa (hydroids)
2. Habitat
– lives in shallow coastal water attached to
substratum
 Morphology
– exists in 2distinctly different forms in its
life
– colonial form (polyps)
– free living form (medusa)

The colonial form

Medusa

Sea Anemone

Introduction
to Platyhelminthes
Triploblastic, bilaterally symmetrical,
acoelomate and unsegmented
Body is flattened dorsoventrally
Digestive system incomplete –a
mouth but no anus
No skeletal, circulatory, or
respiratory systems; excretory
system of many flame cells joined to
excretory ducts

Nervous system primitively a simple
nerve net, but advanced forms have a
pair of anterior ganglia or a nerve
ring and 1 to3 pairs of longitudinal
nerve cords with transverse
connectives
Complex hermaphroditic
reproductive system; internal
fertilization; development either
direct or with 1 or more larval stages

Adaptive features
Gaseous exchange Flattened, diffusion
Nutrition Holozoic in planaria or parasitic
Support no
Fertilization Hermaphrodite
Embryo develop Egg external
Movement muscle
Special features Bilateral symmetrical, acoelomate

Planaria
1. Habitat
– the common planaria inhabit cool ,clear
permanent lakes and streams, where
they avoid light by clinging to the
under surface of stones or logs in the
water

Structure

Cross section
of body

Tapeworm
1. Habitat
– The adult stage lives in the small of its
primary host (e.g. man) i.e. it is an
endoparasite
– The immature stage lives inside the
body of the secondary host (e.g. pig)

Structure

Life Cycle

Nematoda

Adaptive features
Gaseous exchange diffusion
Nutrition Parasite, holozoic
Support no
Fertilization hermaphrodite
Embryo develop egg
Movement muscle
Special features Bilateral symmetrical, no segment

&

External view of an
earthworm

Introduction to annelids
Annelids…for example as earthworm
belong to the Phylum Annelida
are segmented worms showing metameric
segmentation
are coleomate animals
 have a fluid-filled body in which the gut and
other organs are suspended
are further classified into three classes:
polychaeta, oligochaeta, hirudinea

Body structure of
annelids
 enlarged coelom to accommodate more
complex internal organs.
 well-developed, fluid-filled coelom and
the tough integument act as a hydrostatic
skeleton.
 Closed circulatory system with blood
vessels running the length of the body and
branching into every segment

 nervous system consists of a brain
connected to a ventral solid nerve cord,
with a ganglion in each segment
 complete digestive system including a
pharynx, stomach, intestine, and accessory
glands
 excretory nephridia in each segment to
collect waste material from coelom and
excrete it through the body wall

Anatomy of a typical annelid,
earthworm

Cross section of through the earthworm
body

Adaptive features
Gaseous exchange Diffusion through skin
Nutrition Holozoic, debris feeder
Support hydroskeleton
Fertilization Internal, hermaphrodite but mate
Embryo develop External, cocoon
Movement Muscle, chaetae
Special features Coelomate, segmented,

Morphology of an earth worm
Earthworms belong to the oligochaeta class.
 They are hermaphroditic with both male and
female gonads.
 The mesoderm of an earthworm splits into
outer and inner layer with coelom in between
which allows:
- space for development of organs
- development of hydrostatic skeleton for
support and movement
- for independent movement of body wall and gut

Metameric segmentation of earthworms
allows for:
- specialization of different body parts
- division of labour
- muscular body wall divides into blocks to
provide independent movement of different
parts of the body
Earthworms have hydroskeletons to maintain
the body shape
Muscles of body wall acts on coelomic fluid
to bring about locomotion, support and
protection

Ecological significance
of earthworms
Soils may barbor 50 to 500 earthworms per
square meter; they contribute to soil formation
and improvement in the following ways:
 tunnels improve aeration and drainage
 dead vegetation is pulled into the soil where
decay by saprobionts take place
 mixing of soil layers
 castings fertilizes the soil

 addition of organic matter by excretion and
death
secretions of gut neutralize acid soils
improving tilth by passing soil through gut
It may be doubted whether there are
many other creatures which have played
so important a part in the history of the
world
Charles Darwin,
1881

Classification of the
Annelida

Arthropoda
segmented appendices

Introduction to arthropods
Arthropods…
 have exoskeleton
 have jointed limbs
 have segmented body
 have dorsal heart and open blood system
grow in stages after moulting (ecdysis)

 because of the size and importance of this
phylum, it is mainly divided into four further
classes:
- crustacea: with very hard exoskeleton
- insecta : body with three parts and three
pairs of legs
- arachnida: body divided into two parts with
four pairs of legs
- myriapoda: with many segments and legs

Adaptive features
Gaseous exchange Trachea, gill
Nutrition Holozoic, parasitic
Support exoskeleton
Fertilization internal
Embryo develop egg
Movement Leg, fly by wing, swim by tail
Special features Segmented, coelomate

The subphylum crustacea
Crustacea contains 30,000 mostly marine
species. A few species live in freshwater. For
example: lobsters, crabs, crayfish, shrimp, etc.
They process...
 two pairs of antennae
 a pair of mandibles
 a pair of compound eyes (usually on stalks)
 two pairs of maxillae on their heads

 a pair of appendages on each body segment
 a head, thorax, and abdomen
 gills for gaseous exchange
 a hard exoskeleton for support and
protection

Anatomy of crustacean (a
prawn)

Marine Copepod
(Crustacean),
Pleuromamma sp.
Marine Copepod
(Crustacean), Actitius
sp.

The subphylum insecta
Insects are the largest group, with probably over
one million identified and named species.
Insects live in almost all terrestrial and
freshwater habitats, with a few species living in
the oceans.
These contribute to insects that they are the
most successful group of animal, and are the
least likely to become extinct.

General characteristics
of the insects
External characteristics
 body comprises head, thorax and abdomen
 three pairs of thoracic walking legs
 two pairs of thoracic wings derived from the
outgrowths of the body wall
 one pair of antennae on the head
 one pair of relatively large compound eyes

Other characteristics
 respiration by a tracheae system with
external openings called spiracles dividing into
finely branched tubules that carry gases
directly to metabolizing tissues
 nervous system include a number of ganglia
and a ventral, double nerve cord
 have a complete and complex digestive
system
very sensitive to sound and have excellent
chemoreceptive abilities.
 have to moult in order to increase in size

Anatomy of the insect
body

Fruit flyFruit Fly. The insect body is divided into head,
thorax (with wings), and a segmented abdomen. The
compound eye of insects is also quite prominent.

Significance of insects
to the ecosystem
Insects are very valuable to us although it
sometimes eat our food, sting us and transmit
diseases. They play a vital role in the ecosystem
by functioning in:
 pollination of many flowering plants
 decomposition of organic materials
 recycling of carbon, nitrogen, and other
essential nutrients

 control of populations of harmful
invertebrate species (including other insects)
 direct production of certain foods like honey
 manufacture of useful products such as silk
and shellac
 become prey of other predators to balance
the food chain
Insecta is most successful animal because it
divided to 70% of all animal species.

Some more examples of
insects
Cockroach -
can transmit
dieseas

Dragonfly
Bee - a born pollinator
of flowers

Moth - can also
pollinate like the
bees
Ant - sometimes
bite the wooden
furniture
Cicad
a