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Characteristics of Animals
Section 27.1
Features of Animals:
# 1: Heterotrophy & Mobility
Animals cannot make their own food
 Most animals move to find food
 Food is digested internally
 Animals have the ability to make rapid,
complex movements
Features of Animals, con’t:
# 2: Multicellularity & Tissues
All animals are made of many
specialized cells
 Animals are the only multicellular group
without cell walls
 All cells are roughly the same size,
regardless of the size of the animal
 Similar cells are organized into functional
groups called tissues
Features of Animals, con’t:
# 3: Diploidy & Sexual Reproduction
Adults cells are diploid – have 2 copies
of each chromosome, 1 from each
 Haploid gametes (sex cells with 1 set of
chromosomes) unite to form offspring
 The zygote (fertilized egg) is diploid
 This allows for genetic diversity
Features of Animals, con’t:
# 4: Blastula Formation
The zygote divides to form a hollow ball
– the blastula
 Cells in the blastula develop three layers
which then develop into different
Ectoderm: skin, nervous system
 Endoderm: digestive & respiratory systems
 Mesoderm: skeleton, muscular, circulatory,
reproductive & excretory systems
Animal Body Plans:
# 1: Symmetry
Asymmetrical – irregular in shape (sponges)
 Radial symmetry – like the spokes of a wheel
(sea anemone)
 Bilateral symmetry – two equal sides
right & left sides
dorsal (back) & ventral (belly)
anterior (head) & posterior (tail)  cephalization
Animal Body Plans, con’t:
# 2: Internal Body Cavity
Found in bilaterally symmetrical animals
 Coelom – the body cavity – fluid-filled space
between body wall & gut; protects the internal
 Three plans:
Acoelomate – no coelom
Pseudocoelomate – body cavity between the
mesoderm and endoderm – “false coelom”
Coelomate – cavity within mesoderm; allows for
greater movement
Animal Body Plans, con’t:
# 3: Segmentation
Segments are repeating body units
 All higher animals have some degree of
segmentation (vertebrae)
Kinds of Animals
35 phyla
 Often divided into 2 major groups:
Invertebrates (without backbones)
 Vertebrates (with backbones)