Introductionto bilateria 2012

1. BILATERAL
SYMMETRY

2. Introduction to
Bilateria
Protostome Bilateria
Subkingdom: Eumetazoa
•Tissues, symmetry, digestive tract, muscles and
nerves
Group Bilateria
Bilateral symmetry, triploblastic, organs and organ
system

4. Bilateral
Symmetry
Bilaterian - Organisms having Bilateral
Symmetry
Animals that are similar to the front and back, upside
and downside.
An animal is considered to have Bilateral Symmetry if
only one plane of bisection of the midsagittal or
midplane produces right and left mirror halves.
Streamlining is allowed by Bilateral Symmetry.

5. Encountering
Resources
Most animals, including Humans, are bilaterally
symmetric. They belong to the group called Bilateria.
Bilateral Symmetry is also known as Plane Symmetry.
Bilateral Symmetry may have evolved when radial
animals began to move up the surface.
The oldest known bilateral animal is the
Vernanimaliacula .

6. Examples
dddd

7. Bilateria Body
Design
Bilateral Symmetry
Cephalized
•Sensory organs concentrated in the head
Triploblastic
Three basic tissue layers

8. Bilateral
Symmetry

9. Bilateral Animal
Lines
Must have evolved in Precambrian
First fossils are Cambrian
Spiralian (3rd Cleave Division is spiral)

12. Cephalization
The differentiation of the front/anterior end of an
organism into a definite head is called Cephalization. It
is considered an evolutionary advancement, and is
accompanied by the concentration of nerve tissues as
well as feeding organisms at the head region with the
purpose of integrating actions/movements in the
nervous system.

13. Targeting
Resources
Cephalization allows the anterior end of the animal to
first encounter food, predators and other external
factors concerning their environment. This is because
the brain as well as sensory organs can be found on
the anterior end. This helps protect and alarms the
organism 24/7.

14. Motile Bacteria
Many, however, not all bacteria is able to display
motility (ex. self-propelled motion) under
circumstances. There are many different types of
motility:
Flagella (sing. Flagellum)
Copious Slime
Internal Structure (ex. Axial Filament)

15. Sessile Bacteria
Bacteria that is not freely able to move about.

16. Musculature
Bilaterians have complete digestive tracts along with a
separate mouth and anus. (Except for some red forms
of bilaterians.) They have an internal body cavity
called a Coelome.
They are Triploblastic which means they have three
tissue layers consisting of the: ectoderm, mesoderm
and endoderm.

17. Compartmentaliz
ation
Compartmentalization or Cellular Compartments
comprise of all the closed parts within the Cytosol of
the (Eukaryotic) cell of an organism. It has 5 types
namely the:
Nuclear compartments including the nucleus.
Intercisternal Space
Organelles
Cytosol

18. Regulated
Compartments
Epithelia is maintains the regulated compartments
Coelenteron or the gut has evolved in cnidarians and
has multiple functions in the taxon.
The bilaterian gut is dedicated to digestion. Therefore
other spaces must assume the responsibility for the
other functions.
Hemal System = new role for the connective tissue.

19. Coeloms
A new fluid filled cavity
It is lined by Mesothelium or Middle Epithelium
Contains a third regulated compartment
It is filled with a fluid called Coelomic Fluid
Functions as a Hydrostat, Transport, Excretion,
Reproduction
Animals with coeloms are called Coelomates

20. Coelom Formation

21. Alternative
Coelomic
Conditions

22. Bilateria
Most animals are considered to be Bilaterians. They
are also known to be the most familiar.
They can be found almost anywhere: seas, land,
freshwater and even on air.
It is important to consider separately the small and
large Biletarians.

23. Development:
Cleavage
Radial/Regulative: Cleavage planes are either parallel
or perpendicular to the polar axis of the egg.
Spiral/Determinate: Cleavage planes are oblique to
the polar axis of the egg.
Bilateral/Determinate: Cleavage planes are oblique to
the polar axis of the egg.

24. Cnidaria
Comes from the Greek word “Cnidos” which means
stinging nettle
Diverse in form
Armed with stinging cells called Nematocysts;
inherited from a common ancestor
Lives in the world’s oceans

25. Hemal System
A system of tubes and ducts which
morphologically parallels that of the water
vascular system in echinoderms, but lies just
orally to it. Its function is not known, but it
seems clear that it does not perform roles
typically associated with a blood-vascular system
in other animals. Possible functions ascribed to
it are internal defense and endocrine, but direct
evidence for either is lacking.

26. Bilateria Body
Features
Bilateral Symmetry
Triploblasty
A Coelome
A Through-Gut
CNS or Central Nervous System