Title: Overview of Animal Diversity
1Overview of Animal Diversity
2General Features of Animals
- Animals are a diverse group of consumers that
share major characteristics - All are heterotrophs
- All are multicellular
- Cells do not have cell walls
- Most are able to move
- All are very diverse in form and habitat
- Most reproduce sexually
- Have a characteristic patterns of embryonic
development - Cells of all animals (except sponges) are
organized into tissues
3Evolution of the Animal Body Plan
- Five key transitions in animal evolution
- Tissues
- Symmetry
- Body cavity
- Development
- Segmentation
4Evolution of the Animal Body Plan
- 1. Evolution of tissues
- Parazoa (Sponges - the simplest animals) lack
defined tissues and organs - Have the ability to disaggregate and aggregate
their cells - Eumetazoa (all other animals) have distinct and
well-defined tissues - Have irreversible differentiation for most cell
types
5Evolution of the Animal Body Plan
- 2. Evolution of symmetry
- Parazoa (sponges) lack any definite symmetry
- Eumetazoa have a symmetry defined along imaginary
axes drawn through the animals body - There are two main types of symmetry
- Radial symmetry
- Bilateral symmetry
6Evolution of the Animal Body Plan
- Radial symmetry
- Body parts arranged around central axis
- Can be bisected into two equal halves in any 2D
plane perpendicular to that axis
7Evolution of the Animal Body Plan
- Bilateral symmetry
- Body has right and left halves that are mirror
images - Body has distinct anterior/posterior and
dorsal/ventral divisions
8Evolution of the Animal Body Plan
- Bilaterally symmetrical animals have two main
advantages over radially symmetrical animals - Cephalization
- Evolution of a definite brain area
- Greater mobility
9Evolution of the Animal Body Plan
- 3. Evolution of a body cavity
- Eumetazoa produce three germ layers
- Outer ectoderm (body coverings and nervous
system) - Middle mesoderm (skeleton and muscles)
- Inner endoderm (digestive organs and intestines)
10Evolution of the Animal Body Plan
- 3. Evolution of a body cavity
- Three basic kinds of body plans
- Acoelomates have no body cavity
11Evolution of the Animal Body Plan
- Pseudocoelomates have a body cavity between
mesoderm and endoderm - Called the pseudocoel
12Evolution of the Animal Body Plan
- Coelomates have a body cavity entirely within the
mesoderm - Called the coelom
13Evolution of the Animal Body Plan
- The body cavity made possible the development of
advanced organs systems - Coelomates developed a circulatory system to flow
nutrients and remove wastes - Open circulatory system blood passes from
vessels into sinuses, mixes with body fluids and
reenters the vessels - Closed circulatory system blood moves
continuously through vessels that are separated
from body fluids
14Evolution of the Animal Body Plan
- 4. Evolution of different patterns of development
- The basic bilaterian pattern of development
- Mitotic cell divisions of the egg form a hollow
ball of cells, called the blastula - Blastula indents to form a 2-layer-thick ball
called a gastrula with - Blastopore - Opening to outside
- Archenteron - Primitive body cavity
15Evolution of the Animal Body Plan
- Bilaterians can be divided into two groups
- Protostomes develop the mouth first from or near
the blastopore - Anus (if present) develops either from blastopore
or another region of embryo - Deuterostomes develop the anus first from the
blastopore - Mouth develops later from another region of the
embryo
16Evolution of the Animal Body Plan
- Deuterostomes differ from protostomes in three
other embryological features - Cleaveage pattern of embryonic cells
- Protostomes - Spiral cleavage
- Deuterostomes - Radial cleavage
- Developmental fate of cells
- Protostomes - Determinate development
- Deuterostomes - Indeterminate development
- Origination of coelom
- Protostomes - Forms simply and directly from the
mesoderm - Deuterostomes - Forms indirectly from the
archenteron
17Evolution of the Animal Body Plan
18Evolution of the Animal Body Plan
- 5. Evolution of segmentation
- Segmentation provides two advantages
- 1. Allows redundant organ systems in adults such
as occurs in the annelids - 2. Allows for more efficient and flexible
movement because each segment can move
independently - Segmentation appeared several times in the
evolution of animals
19Traditional Classification of Animals
- Multicellular animals, or metazoans, are
traditionally divided into 36 or so distinct
phyla based on shared anatomy and embryology - Metazoans are divided into two main branches
- Parazoa - Lack symmetry and tissues
- Eumetazoa - Have symmetry and tissues
- Diploblastic - Have two germ layers
- Triploblastic - Have three germ layers
20A New Look At Metazoans
- The traditional animal phylogeny is being
reevaluated using molecular data - Myzostomids are marine animals that are parasites
of echinoderms - Have no body cavity and only incomplete
segmentation and so have been allied with
annelids
21A New Look At Metazoans
- Recent analysis of the translation machinery
revealed that myzostomids have no close link to
the annelids at all
- Instead, they are more closely allied with the
flatworms (planaria and tapeworms)
22A New Look At Metazoans
- It seems that key morphological characters used
in traditional classification are not necessarily
correct - Molecular systematics uses unique sequences
within certain genes to identify clusters of
related groups
23A New Look At Metazoans
- Most new phylogenies agree on two revolutionary
features - Separation of annelids and arthropods into
different clades - Division of the protostome group into Ecdysozoa
and Spiralia - The latter is then broken down into
Lophotrochozoa and Platyzoa
24A New Look At Metazoans
Examples can be found in Table 32.2 of Raven et
al.
25Evolutionary Developmental Biology
- Most taxonomists agree that the animal kingdom is
monophyletic - Three prominent hypotheses have been proposed for
the origin of metazoans from single-celled
protists -
26Evolutionary Developmental Biology
- 1. The multinucleate hypothesis
- 2. The colonial flagellate hypothesis
- 3. The polyphyletic origin hypothesis
- Molecular systematics using rRNA sequences
settles this argument in favor of the colonial
flagellate hypothesis