• Animals have different patterns of symmetry, the arrangement of body parts around a central axis

– Asymmetry – no general body plan

– Example: Sponges

Asymmetry

• Radial symmetry – body can be divided into equal parts around a central axis

• Example: starfish, jellyfish

Oral = side containing the mouth

StarfishMorro Bay, CA

Radial Symmetry

Bilateral Symmetry

• Bilateral symmetry – body can be divided along one plane of symmetry into two mirror halves

• Example: humans, crocodiles, crayfish

Compare the Difference

Symmetrical

versus no symmetry

Bilaterally symmetrical animals can be divided into the following planes:

• Anterior – front end

• Posterior – back end

• Ventral – underside (belly)

• Dorsal – back (top side)

Anterior Posterior

Ventral

Dorsal

CephalizationBilaterally symmetrical

animals also have cephalization, which is the concentration of nerve and sensory tissue at the anterior end of the organism

CNS – CentralNervous System

Note the formation of the embryonic tissue layers: endoderm, mesoderm,

ectoderm

Animals have different body plans based on the development of body cavities

Acoelomate Pseudocoelomate Eucoelomate

Body Cavities• Acoelomate – animal that lacks a body cavity

• Pseudocoelomate – animal that has a cavity between the mesoderm and endoderm

(Not a truebody cavity..thus pseudo)

Body Cavities

• Coelomate / Eucoelomate – animal that has a cavity that develops within the mesoderm ( a true coelom/body cavity)

Animalia• One main distinction between

the phyla is the presence of a notochord, which can develop into a vertebral column (backbone)

• If animals do NOT possess a backbone, they are invertebrates, and if they do possess a backbone, they are called vertebrates

Vertebrate

Invertebrate

Invertebrate Animals

The following phyla will be discussed in more detail in class:

• Phylum Porifera

• Phylum Cnidaria

• Phylum Platyhelminthes

• Phylum Nematoda

Cnidaria

Porifera

Nomura Jellyfish

Platyhelminthes

Nematoda

Invertebrate Animals

• Phylum Mollusca

• Phylum Annelida

• Phylum Arthropoda

• Phylum Echinodermata

Mollusca

Annelida

Arthropoda

Echinodermata

Polychete worm

Vertebrate Animals• Phylum Chordata

– Class Agnatha– Class Chondrichthyes– Class Osteichthyes– Class Amphibia– Class Reptilia– Class Aves– Class Mammalia