2. Introduction
• One million animal species have been described
and named so far.
• 4 to 10 million animal species awaits discovery
and description.
• First animals may have evolved 3 billion years
ago. Earth is 4.5 billion years old
• First metazoan animal similar to the present day
animals appear during the Cambrian Period
3. • Cambrian Explosion- the sudden appearance and
diversification of complex animals over some
550 million years ago.
• Before we can consider the evolutionary
interrelationships among different groups of
organisms we must sort the millions of animals
species into categories.
• Sorting out by means of their similarity and
differences
4. Classification by Cell Number, Embryonic
Patterns and Body Symmetry
• Single celled or unicellular
• Multicellular or many celled- Metazoans
• True metazoans are multicellular, diploid
organisms, develops into blastula
• Widely agreed that the earliest
invertebrates are unicellular and
multicellularity was an evolutionary
innovation
5. General body Form
• Bilateral Symmetry-possessing right and
left sides that are approximate mirror
images of each other
• Bilateral symmetry is highly correlated with
cephalization- concentration of the nervous
and sensory tissues and organs at one end
of the animal resulting in distinct anterior
and posterior ends.
7. General body Form ( cont )
• Radial symmetry- organism can be divided
into two approximately equal halves by any
cut that passes through the center of the
animal.
• Assymetrical- possessing no symmetry at
all, that is the animal cannot be equally
divided
8. Classification by Developmental
Pattern
• Based on number of Germ layers formed
during embryogenesis
• Germ layers- group of cells behaving as a
unit during the early stages of embryonic
development and giving rise to distinctly
different tissue and or organ systems in the
adult.
9. • Diploblastic- 2 germ layers; ectoderm and
endoderm
• Triploblastic- 3 germ layers; ectoderm,
endoderm and mesoderm- always at the
middle of ectoderm and endoderm
• Ectoderm outer layer- give rise to the skin
• Endoderm – inner layer give rise to the
internal organs
11. Based on presence or absence of
Coelom
1. Acoelomic- without body cavity, region
lying between the outer body wall and gut is
solid
• 2. Pseudocoelomic- not true body cavity;
region between the outer body wall and the
gut is a fluid filled cavity
• 3. Eucoelomic- true body cavity; an internal
fluid filled body cavity lying between the gut
and outer body wall musculature and lined
with tissue derived from embryonic
mesoderm
13. Classification of Animal Based From Coelom
Formation
• Schizocoely-coelom formation occurs by
gradual enlargement of a split in the
mesoderm; present among protostomes
• Enterocoely- coelom is formed from the
evagination of the archenteron into the
blastocoel of the embryo; present among
deuterostomes
• Whether the coelom is formed by enterocoely
or schizocoely the end result is similar
15. Depending on Mouth Formation
( Stomes )
• Protostomes ( first mouth )- mouth forms
from the blastophore
- number of coelomic cavities formed is
highly variable
• Deuterostomes ( second mouth )- mouth
arises away from the embryonic blastophore
- number of coelomic cavities divides into 3
coelomic pouches
16. Types of Cleavage
• Radial- the spindles of a given cell and the
cleavage planes are oriented either parallel or
perpendicular to the animal-vegetal axis
• Daughter cells derived from a division in
which the cleavage plane is parallel to the
animal –vegetal axis ends up lying in the
same plane as the original mother cell
• Two daughter cell resulting from a division
perpendicular to the animal-vegetal axis come
to lie directly one atop the other with the
center of the upper cell directly over the
center of the underlying cell
17. Types of Cleavage
• Spiral- the spindle axes of cells are oriented at
45 degrees angles to the animal-vegetal axis;
the division line may not pass through the
center of the dividing cell
• As a result the eight cell stage consists of
micromeres –group of smaller cells lying in
the spaces between the underlying
macromeres- larger cells
• Cell division continues in this fashion , with
the cleavage planes oblique to the polar axis
of the embryo
20. Fate of Cells with Respect to Cleaving
Embryos
• In Deuterostomes, one can separate the cells
of a two-cell or four cell embryo and each cell
will typically develop into small but complete
and fully functional animal- indeterminate or
regulative cleavage.
• In Protostomes- developmental potential of
each cell is irrevocably determined at the first
cleavage- determinate or mosaic cleavage
• Protostomes never produce identical twins
21. • Protostomes –much of the mesodermal tissue
derives from a single cell of the 64 –cell
embryo, located at the edge of the blastopore
• Deuterostomes produces embryo from the
walls of the archenteron
• Polar lobe- produced by some protostome
only – conspicuous bulge of cytoplasm that
forms prior to cell division.The lobe contains
no nuclear material
22. Carolus Linnaeus, father of Taxonomy, gave the
binomial system of naming organisms. The first part of the
system is the genus where the species belongs and the
second part refers to one species within the genus.
23. Hierarchical Classification
• Beyond the grouping of organism
within the genera, taxonomy
extends into broader categories.
Beyond the genus is the family,
order, classes, phyla kingdoms
and domains.
24. Scientist classifies organisms by getting the general similarities of the
organisms. Next, scientists gets more specific and identify more detailed similarities.
This classifies the phylum. More detailed similarities are identified and so on.
25.
26. Classification and Phylogeny
• Systematics has some other goals beyond
classifying organisms. By comparing the
similarities of various organism, Scientists
manage to trace the evolutionary history of a
species, which is phylogeny. Through hierarchical
classification of several species, it can form a
phylogenetic tree. This can be based on fossil
records, homologous structure, comparison of
DNA and cladistic analysis
27.
28.
29. Sorting through Homology
• This is classification by looking at the same
structures of several species.
• Species of different evolutionary branch may
have similar structures as it is the result of
adaptation and natural selection. This is called
convergent evolution. For example the wings of
insect and birds.
30.
31. Molecular Biology used in
classification
• This is classification by comparing the
genes and proteins of organisms.
Scientists arranged similarly structured
genes and inferred that the organisms
have a common ancestry.
32. Cladistic Approach
• This method is based on derived similarities.
Unlike other classification, this is based on the
overall similarities, in other words it looks for
several similarities in determining the
evolutionary relationship.
• Willi Hennig is widely regarded as the founder of
cladistics.
• The advantage of this approach is that all data
that forms the basis of postulated relationships is
shown, which often suggests new relationships,
and can be more readily tested.
