Animal phylogeny can be determined, in part, by body plans and

the ways animals develop.

Section 2: Animal Body Plans

K

What I Know

W

What I Want to Find Out

L

What I Learned

Essential Questions

• How are animal body plans related to phylogeny?

• How are body cavities related to animal phylogeny?

• What are the two types of coelomate development?

Animal Body PlansCopyright © McGraw-Hill Education

Review

• phylogeny

New

• symmetry

• radial symmetry

• bilateral symmetry

• anterior

• posterior

• cephalization

• dorsal

• ventral

• coelom

• pseudocoelom

• acoelomate

• protostome

• deuterostome

Animal Body PlansCopyright © McGraw-Hill Education

Vocabulary

Evolution of Animal Body Plans

• Anatomical features in animals’ body plans mark the branching points on the

evolutionary tree.

• Relationships on this tree are inferred by studying similarities in

embryological development and shared anatomical features.

Animal Body PlansCopyright © McGraw-Hill Education

Animal Body PlansCopyright © McGraw-Hill Education

Development of Tissues

• The first major change in body plan was the development of tissues.

• Sponges are the only animal without true tissues.

Symmetry

• Symmetry is the next branching point after tissues.

• Symmetry is the balance or similarity of body structures of an organism.

Animal Body PlansCopyright © McGraw-Hill Education

Symmetry

Asymmetry• Irregular shape, no symmetry or balance in body structures.

Radial symmetry

• An animal with radial symmetry can be divided along any plane, through a

central axis, into roughly equal halves.

Bilateral symmetry

• Bilateral symmetry means an animal can be divided into mirror image halves

along only one plane.

Animal Body PlansCopyright © McGraw-Hill Education

Invertebrates

BrainPOP

FPO

Add link to BrainPOP from page 700 here.

Animal Body PlansCopyright © McGraw-Hill Education

Symmetry

Bilateral symmetry

• Animals with bilateral symmetry also have anterior (head) and posterior (tail)

ends.

• This body plan is called cephalization, and involves a tendency to

concentrate nervous tissue and sensory organs at the anterior end of the

animal.

Animal Body PlansCopyright © McGraw-Hill Education

Body Cavities

• Animals with bilateral symmetry have a gut, which is either a sac

inside the body or a tube that runs through the body, where food is

digested.

• A saclike gut has one opening, a tubelike gut has two.

Animal Body PlansCopyright © McGraw-Hill Education

Body Cavities

Coelomates

• A coelom is a mesoderm-lined, fluid-filled cavity between the gut

and the outside body wall.

• Specialized organ and body systems develop from the mesoderm

that encloses and lines the coelom.

Animal Body PlansCopyright © McGraw-Hill Education

Body Cavities

Pseudocoelomates

• A pseudocoelom is a fluid-filled body cavity that develops between the

mesoderm and the endoderm.

• Only partially lined with mesoderm.

Animal Body PlansCopyright © McGraw-Hill Education

Body Cavities

Acoelomates

• Acoelomates do not have a coelom.

• Have solid bodies without a fluid-filled body cavity between the gut and

the body wall

• Nutrients and wastes diffuse between cells; no circulatory system

Animal Body PlansCopyright © McGraw-Hill Education

Development in Coelomate Animals

Protostomes

• Organisms that are protostomes develop mouths from the first opening in the

gastrula.

• As the embryo develops, the mesoderm splits down the middle to form the

coelom.

Animal Body PlansCopyright © McGraw-Hill Education

Development in Coelomate Animals

Deuterostomes

• In organisms that are deuterostomes, the anus develops from the first

opening in the gastrula.

• Coelom develops from two pouches in the mesoderm.

Animal Body PlansCopyright © McGraw-Hill Education

Visualizing Protostome and Deuterostome Development

Animation

FPO

Add link to animation from page 703 (Figure 12) here.

Animal Body PlansCopyright © McGraw-Hill Education

Segmentation

• Segmented animals can be “put together” from a succession of similar parts.

• Can survive damage to one segment

• Movement is more effective

Animal Body PlansCopyright © McGraw-Hill Education

Animal Body PlansCopyright © McGraw-Hill Education

Review

Essential Questions

• How are animal body plans related to phylogeny?

• How are body cavities related to animal phylogeny?

• What are the two types of coelomate development?

Vocabulary

• symmetry

• radial symmetry

• bilateral symmetry

• anterior

• posterior

• cephalization

• dorsal

• ventral

• coelom

• pseudocoelom

• acoelomate

• protostome

• deuterostome