introductionto bilateria 2012
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BILATERAL SYMMETRY
Introduction to Bilateria
Protostome Bilateria
Subkingdom: Eumetazoa
Tissues, symmetry, digestive tract, muscles and nerves
Group Bilateria
Bilateral symmetry, triploblastic, organs and organ system
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.
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.
Examples
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Bilateria Body Design
Bilateral Symmetry
Cephalized
Sensory organs concentrated in the head
Triploblastic
Three basic tissue layers
Bilateral Symmetry
Bilateral Animal Lines
Must have evolved in Precambrian
First fossils are Cambrian
Spiralian (3rd Cleave Division is spiral)
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.
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.
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)
Sessile Bacteria
Bacteria that is not freely able to move about.
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.
Compartmentalization
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
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.
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
Coelom Formation
Alternative Coelomic Conditions
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.
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.
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
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.
Bilateria Body Features
Bilateral Symmetry
Triploblasty
A Coelome
A Through-Gut
CNS or Central Nervous System