1. 2.

3.

4.

5. 6. 7.

Which numbers represent chordates and which numbers represent invertebrates?

25.2 Animal Body Plans and Evolution

Features of Body Plans• Each animal phylum has a unique organization of

particular body structures that is often referred to as a body plan.

• Features of body plans include:– Levels of organization– Body symmetry– Differentiation of germ layers– Formation of body cavities– Patterns of embryonic development– Segmentation– Cephalization– Limb formation

Levels of Organization• Animals have specialized cells that are organized into

tissues.• There are several types of tissues found in animals:

– Epithelial tissues- cover body surfaces inside and out, are also thin and flat. • Example: epithelial tissues line lungs and allow

gases to easily diffuse through– Muscle tissues– Connective tissues

• Tissues combine during growth and development to form organs and organ systems to carry out complex functions

Body Symmetry• Bodies of most animals exhibit some sort of

symmetry• There are two different forms of symmetry

– Radial symmetry: any number of imaginary planes drawn through the center of the body could divide into equal halves. Example: Sea anemone

– Bilateral symmetry: a single imaginary plane divides the body into left and right sides that are mirror images of each other.

• Animals with bilateral symmetry have the following– A definite front: also known as the anterior– A definite end: also known as the posterior– An upper side: also known as the dorsal side– A lower side: also known as the ventral side

Differentiation of Germ Layers

• During embryological development the cells of most animal embryos differentiate into 3 germ layers– 1. Endoderm: the innermost germ layer, develops

into linings of the digestive tract and much of the respiratory system

– 2. Mesoderm: the middle layer, gives rise to the muscles and much of the circulatory, reproductive, and excretory organ systems

– 3. Ectoderm: the outermost layer, produces sense organs, nerves, and the outer layer of skin

Formation of a Body Cavity• Most animals have a body cavity, which is a fluid-filled space between the

digestive tract and body wall• Body cavities provide space for internal organs to suspend and room for

organs to grow• Most complex animal phyla have a true coelom- a body cavity that develops

within the mesoderm and is completely lined with tissue derived from the mesoderm• The coelom wraps around the gut and internal organs are suspended in it• Animals with a coelom allows the animals to move without damaging the

internal organs or interfering with the organ’s function• Acoelomates are invertebrates that lack a coelom

• The are of an acoelomate’s body wall and gut is completely filled with tissues

• Some invertebrate groups have a pseudocoelom, which is only partially lined with mesoderm • This false coelom is filled with liquid that can act like a skeleton and

provide support

Patterns of Embryological Development

• Every animal that reproduces begins as a zygote (a fertilized egg)

• At the beginning of development a zygote forms a blastula, which is a hollow ball of cells like an inflated balloon

• The blastula develops into the digestive tract by folding in on itself and developing a long elongated tube that runs from one end to the other

• In the beginning the digestive tract has only one opening, called the blastopore

Patterns of Embryological Development

• An efficient digestive system needs two openings: a mouth through which food enters and an anus through which waste exits

• Protostomes: the blastopore becomes the mouth and the anus becomes the second opening, which develops at the opposite end of the tube

• Examples: flatworms, earthworms, snails, clams, spiders, and insects

• Deuterotomes: the blastopore becomes the anus, and the mouth is formed from the second opening that develops– Chordates and echinoderms (sea stars) are deuterotomes,

which indicates that echinoderms are closely related to chordates

Segmentation: Repeating Parts• Segmentation occurs as many bilateral

symmetrical animals develop, their bodies become divided into numerous repeated parts, or segments

• Segmented animals such as worms, insects, and vertebrates have at least some internal and external body parts that repeat on each side of the body

• The most successful animals, including humans, have bilateral symmetry and segmentation

Cephalization: Head Formation• Animals with bilateral symmetry typical exhibit

cephalization- the concentration of sense organs and nerve cells at their anterior end

• The most successful animals including arthropods and vertebrates exhibit pronounced cephalization

• Insect and vertebrate embryos heads are formed by fusion and specialization of several body segments during development – As the segments fuse the external and internal parts combine

in ways that concentrate sense organs in the head, such as the eyes

– Nerve cells that process information and “decide” what an animal should do are also found in the head

– Animals with a head move in a head first direction because this way the concentration of sense organs and nerve cells come in contact with the new environment first

Limb Formation: Legs, Flippers, and Wings

• Segmented, bilaterally symmetrical animals typically have appendages on both sides of the body.

• The types of appendages vary depending on the animal. Examples:

• Bristles in worms * Flippers in dolphins• Jointed legs in spiders * Wings in dragonflies

• These different kinds of appendages have evolved several times, and have been lost several times, in various animal groups

• Limb formation and segmentation have evolved to allow animals to be more flexible and have improved movement

Limb Formation: Legs, Flippers, and Wings

Animal Type:

Levels of organization Cells, tissues, organs?Body symmetry Bilateral, radial?Germ layers 1,2,3..?Body Cavity Coelom, Pseudocoelom,

Acoelom..?Embryological Development Protostomes, DeuterostomeSegmentation Absent, Present?Cephalization Present, Absent?

Animals to include on chart: •Sponges *Cnidarians•Flatworms *Roundworms•Annelids *Mollusks•Arthropods *Echinoderms•Chordates

CnidariansLevels of organization

Specialized cells, Tissues

Body symmetry Radial symmetryGerm layers TwoBody Cavity AcoelomateEmbryological Development

___

Segmentation AbsentCephalization Absent

25.2 Body Plans and Evolution Vocabulary

• Radial Symmetry: any number of imaginary planes drawn through the center of the body could divide into equal halves.

• Bilateral Symmetry: a single imaginary plane divides the body into left and right sides that are mirror images of each other.

• Endoderm: the innermost germ layer, develops into linings of the digestive tract and much of the respiratory system

• Mesoderm: the middle layer, gives rise to the muscles and much of the circulatory, reproductive, and excretory organ systems

• Ectoderm: the outermost layer, produces sense organs, nerves, and the outer layer of skin

• Coelom: a body cavity that develops within the mesoderm and is completely lined with tissue derived from the mesoderm

25.2 Body Plans and Evolution Vocabulary

• Pseudocoelom: which is only partially lined with mesoderm • Zygote: a fertilized egg• Blastula: a hollow ball of cells like an inflated balloon that

develops into the digestive tract by folding in on itself and developing a long elongated tube that runs from end to the other

• Protostomes: the blastopore becomes the mouth and the anus becomes the second opening, which develops at the opposite end of the tube

• Deuterostomes: the blastopore becomes the anus, and the mouth is formed from the second opening that develops

• Cephalization: the concentration of sense organs and nerve cells at their anterior end

25.2 Assessment

• 1a. List eight features of animal body plans.• 1b. How is the embryology of echinoderms

similar to that of vertebrates? What might this similarity indicate about their evolutionary relationship.