Animal DiversityKEY FEATURES OF BODY PLANS

ABBOTTS COLLEGE

PAGE 73

DARWINS THEORY OF EVOLUTION

Organisms are descended from common ancestors

This theory guides scientists in their search for order in the astounding diversity of animal life on earth

The science of taxonomy names and classifies different species to illustrate this order

PHYLA

Animals can be grouped into phyla according to similarities in various features of their basic structure(body plan)

This makes it possible to understand the evolutionary development of the group

Body plan = the general similarities in development, form and function among members of a particular phylum

PAGE 73

The term phylum is one of seven major categories that are used to classify organisms. In order of broad to specific, these seven categories are: Kingdom, Phylum, Class, Order, Family, Genus, and Species. Carolus Linnaeus developed this system of classification in the 18th century

THE FEATURES OF THE BASIC BODY PLAN INCLUDE:

Body Symmetry Number of tissue layers developed from the

embryo The number of openings in the gut The presence or absence of a coelom (body

cavity) and blood systems

BODY SYMMETRY

The body plans of multicellular organisms are either asymmetrical, radially symmetry or bilaterally symmetrical

Asymmetry: Having no symmetry

Sponges

PAGE 73

ASYMMETRY

Having no symmetry

Sponges

PAGE 73

RADIAL SYMMETRY

the body parts are arranged around a central axis

and can be divided into mirror images by an imaginary line through any vertical plane

RADIAL SYMMETRY

Tubular, vase or bowled shaped animals that have a mouth at one end are usually radial symmetrical

Radial symmetry is common in sessile, free-floating or weakly swimming animals.

They need to interact with their surroundings equally well on all sides

BILATERAL SYMMETRY

the body can only be divided into mirror images by an imaginary line through one plane

If cut lengthwise, the y form left and right halves (mirror images)

Also have a top and a bottom And a front and a back This type of symmetry is suited to animals that

move about

BILATERAL SYMMETRY

They show cephalization which allows them to become aware of the environments around them as they move forward

This increases their chance of finding food or predators

Cephalisation = concentration of sense organs, feeding appendages and nervous tissue near the anterior end of the animal

CEPHALIZATION

TISSUE LAYERS

Germ layers formed from developed embryo(zygote)

Upper layer (ectoderm) forms the epithelium of the body surface (skin) and the nervous system

Lower layer (endoderm) forms the wall of the digestive system (gut)

Mesoderm is formed by an interaction between the ectoderm and endoderm

Diploblastic animals only have two layers of tissuesEctoderm and endoderm

Triploblastic animals have three layers of ttissuesEctoderm, mesoderm and endoderm

Why is the development of mesoderm so important?

The development of the mesoderm was a tremendous evolutionary advancement

Mesoderm plays a role in the formation of tissues eg connective tissue, cartilage, bone

and organs eg reproductive organs and systems eg blood and lymph sytems

Page 74

NUMBER OF OPENINGS IN THE GUT

Single opening Two openings

PAGE 74

Gut =The alimentary canal or a portion thereof, especially the intestine or stomach.

NUMBER OF OPENINGS IN THE GUT

Single opening Primitive animals Sac like digestive

cavity Take in food and

expel waste out of the same opening

Not an efficient system

Porifera and Cnidarians

NUMBER OF OPENINGS IN THE GUT

Two openings It allows food to be

continually taken through the mouth, digested and the waste released from the anus

This body plan allows specialization of parts along the tube, such as a stomach, intestine, etc.

BODY CAVITIES/COELOM

A coelom is an internal fluid filled body cavity that develops in the mesoderm of triploblastic animals

The coelom separates the digestive tract from the body wall

Diploblastic animals do not have a coelom

In triploblastic animals we distinguish between:

acoelomate, pseudocoelomate and

coelomate animals

PAGE 74

ACOELOMATE ANIMALS

These animals have no coelom (body cavity) in the mesoderm

Can be diploblastic or triploblastic

PSEUDOCOELOMATE

Have a body cavity, Not seen as a true coelom

because it is not completely in the mesoderm

NOT IN TEXTBOOKADD TO WORKBOOK

COELOMATE

Have a body cavity in the mesoderm

They are more advanced than acoelomate animals

ADVANTAGES OF A COELOM

Allows space for larger and more complex organs and systems to develop eg digestive organs, muscular system, blood system and allows animals to reach a considerable size

In soft bodied animals the fluid in the skeleton can act as a hydrostatic skeleton (against which muscles can act)

Allows the digestive system and body wall to move independently

PAGE 75

THE END