Animals
Animal Bodies

Morphology is
◦ the branch of biology dealing with the form and
structure of organisms.

Symmetry is
◦ the proper proportion of the parts of a body
with respect to one another and with regard to
size and form.
Body Structure
Radial Symmetry
 Basic body plan where the organism can
be divided into similar halves by passing a
plane at any angle along a central axis.
 Characteristic of sessile and bottomdwelling animals, as the sea anemone and
starfish.
Patterns of Symmetry
Bilateral Symmetry
 Basic body plan where the left and right
sides of the organism can be divided into
approximate mirror images of each other
along the midline.
 Dorsal - back
 Ventral - tummy
 Anterior - head
 Posterior – rear end
Bilateral Symmetry – most animals…
 Cephalization
◦ specialization of the body with
sensory and neural organs in an
anterior head
Bilateral Symmetry…
Germ Layers – layers formed during very
early development of most animals

1. ectoderm = outside layer

2. endoderm = inside layer

3. mesoderm = layer in between the
above two
Patterns of Symmetry
Most animals have some type of body
cavity.
 Body Cavity

◦ Fluid-filled space between the digestive tract
and the outer wall of the body
Examples:
 FLATWORM: three germ layers; solid
body – lack body cavity.
 ROUNDWORM: Body cavity aids in
movement
◦ Provides a firm structure against which muscles
can contract
Body Cavities…
A body cavity also allows more freedom of
movement for the animal
 The fluid in the cavity is a reservoir for
the transport for nutrients and wastes.
◦ these diffuse in/out of the animal’s body
cells.

Body Cavities…
ANIMAL DIVERSITY
 Animal phyla shown on the same branch
of the phylogenetic tree are thought to be
more closely related to each other than
they are to other animals.
 Likewise, animals shown in different parts
of the tree are thought to be more
distantly related.

Animal Diversity…


Multicellularity and a limited degree of cell
specialization – characteristic of sponges
Sponges have no organized body shape and no
true tissues.

True tissues in two layers – found in the
cnidarians (hydra, jellyfish, etc.) and the
ctenophores (exclusively marine, invertebrates)

True tissues in three layers and bilateral
symmetry – characterize all of the other animal
phyla
phylogenetic categories are based on

◦ the absence or presence and type of body cavity
◦ fundamental patterns of development
Animal Diversity…
Invertebrates
 Absence of a backbone
 Greatest number of animal species
 Most of the animals alive today

Animal Diversity…
Chordates
 Refers to the notochord
◦ A firm, flexible rod of tissue located in the dorsal
part of the body (the back).
◦ At some stage of development, all chordates have a
notochord, dorsal nerve cord, pharyngeal pouches,
and a post anal tail.

Dorsal nerve cord

Pharyngeal pouches

Postanal tail
◦ Hollow tube lying just above (dorsal to) the
notochord.
◦ Small outpockets of the anterior part of the
digestive tract.
◦ Consists of muscle tissue and lies behind the
posterior opening of the digestive tract.
Animal Diversity…
In most vertebrates…
 The dorsal nerve cord develops into the
brain and the spinal cord.

Pharyngeal pouches evolved into gills –
used for breathing.
In most vertebrates, the notochord is
seen only in the embryonic stage.
 It is replaced by the backbone early in
development.

Animal Diversity…
Vertebrates…
 Make up only one subphylum of the
phylogenetic tree of all animals.
 Humans are vertebrates.
 Humans interact extensively with many other
vertebrates.
◦ fishes
◦ birds
◦ mammals

All of these are primary food sources for
humans.
Animal Diversity…