Class Roadmap
1
I. Introduction to Zoology
A. What is an Animal?
Animal life began in Precambrian seas
with the evolution of multicellular forms
that lived by eating other organisms. Early
animals populated seas, fresh water, and
eventually the land.
B. Three things we focus on:
1. Structure
2. Nutrition
3. Life history define animals.
C. Structure, nutrition, and life
history define animals.
1. Animals are multicellular, heterotrophic,
and eukaryotes. In contrast to autotrophic
nutrition of plants and algae, animals must
take into their bodies preformed organic
chemicals. Animals can do this by
ingestion-eating other organisms or
organic material that is decomposing
2. Animals lack cell walls that provide
strong support in the bodies of plants and
fungi. The multicellular bodies of animals
are held together by structural proteins,
the most abundant being collagen.
3. Also unique among
animals are two types of
tissues responsible for
impulse conductions and
movement: nervous tissue
and muscle tissue.
4. Most animals reproduce
sexually, with the diploid
stage usually dominating
the cycle. ***See diagram
on next slide
Cleavage
Blastula
Gastrulation
Gastrula
Cell Cycle: G1, S, G2, and Mitosis
D. Did the animal kingdom evolve from a
flagellated protist?
• Most scientist agree that
the animal kingdom in
monophyletic; animal
lineages can be traced
back to a common
ancestor.
• Likely a a flagellated
protist over 700 million
years ago.
• Related to a
choanoflagellate, which
arose about a billion
years ago.
Going From A single cell to
Multicellular Organism
This is an example
of Phylogenic Tree
As an A & P class
will work from left to
right throughout
the 1st marking
period
•Do you see any
patterns?
Introduction
How did we
get here?
II. Chapter 8
A. Early Concepts: Preformation versus
Epigenesis
a. Mystery of development in the 17th and
18th centuries
1. Naturalist-philosophers claimed that
young animals were preformed in eggs
and that development was simply a matter
of unfolding what was already there.
2. A 17th Century Dutch
histologist thought he
saw a preformed
human infant in
sperm in a
microscope he made.
3. 1759 Embryologist Kasper Wolff
• Studied the development of a chick
• No preformed individual, only
undifferentiated granular material that became
arranged into layers.
• This process was called epigenesis-a fertilized
egg contains the building materials for
development.
• Unknown forces control these actions???
B. Hierarchy of Development Decisions
• Course of
Differentiation:
cytoplasmic location
and induction
• Cell types that make
up the body do not
just “unfold”, but arise
from conditions
created in preceding
stages.
C. Fertilization (1n) egg + (1n) sperm=(2n)
zygote
• The initial event in development in sexual
reproduction is fertilization, the union of
male and female gametes to form a
zygote.
• Recombinant of parental and maternal
genes
• Parthenogenesis-development without
fertilization (Example some fish and
salamanders)
D. Cleavage and Early Development
• During cleavage the embryo divides repeatedly to
convert the large cytoplasmic mass into a large
cluster of small maneuverable cells called
Blastomeres.
E. Cleavage and Early Development
• No growth during this period, only
subdivisions of mass, which continues
until somatic cell size is attained. Think of
it a origami!!!!
• So, what are somatic cells?
• At the end of cleavage 100s to 1000s of
cells
Cleavage and Early
Development
Look at the Diagram
to see an example of
a VEGETAL POLE
AND ANIMAL POLE
•What is the role of
the yolk?
•Do the cells at the
poles divide at the
same rate?
F. What can we learn from Development?
• Developmental Biology is a growing field!!
• How can a zygote, a single layer cell,
produce a multitude of body parts in an
organism and how gene expressions
proceeds.
• Search for commonalities among
organisms.
II. An overview of Development Following
Cleavage
A. Blastulation
• Cleavage subdivides the mass of zygote
until a cluster of cells called a blastula is
formed (looks like a hollow mass of cells).
• In most animals, the cells are arranged
around a central fluid-filled cavity called a
blastocoel.
• Formation of a blastula stage, with its one
layer of germ cells, occurs in all
multicellular animlas.
B. Gastrulation and Formation of Two Germ Layers
a. Gastrulation converts the spherical blastula into
a more complex configuration and forms a
second germ layer.
– One side of the blastula bends inward in a
process called invagination, forming a new
internal cavity. Picture pushing in a beach
ball-the inward region forms a pouch.
– The internal pouch is the gut cavity called an
archenteron or gastrocoel.
– The opening to the gut, where the inward
bending began, is the blastopore.
Gastrulation and Formation of Two Germ Layers
C. The gastrula stage has two layers:
a. An outer layer of cells surrounding the blastocoel,
called ectoderm
b. An inner layer of cells is called endoderm
– The gut opens only at the blastopore it is called a
blind or incomplete gut. Animals with a blind gut must
consume food completely digested, or the remains of
the food egested through the mouth. Ex sea
anemones and flatworms.
– Most animals have a complete gut with a second
opening, the anus.
c. Formation of the Mesoderm, a
Third layer
i. Multicellular
animals (not
sponges) proceed
blastula to
gastrula
• Two germ layers
called
DIPLOBLASTIC
• Three germ layers
called
TRIPLOBLASTIC
– The third layer
is called
mesoderm
C. Formation of the Coelom
• Coelomates are animals
with a true coelom, a fluid
filled body cavity
completely lined by
tissues derived from
mesoderm.
• The inner and outer
layers of tissue that
surround the cavity
connect dorsally and
ventrally to form
mesenteries that
suspend the internal
organs.
Animals can be divided
into three body type:
1. Acoelomate
2. Pseudocoelomate
3. Coelomate
D. Protostome vs Deuterostome in Coelomates
• Mollusks, annelids, arthropods and some other
phyla are collectively called protostomes.
• Echinoderms and chordates are called
deuterostomes.
4 Fundamental differences between the two
groups:
***** See Class Handout or next slide
• Which process Radial or Spiral Cleavage will
develop identical twins?
Example: Identical twins
Mechanisms of Development
• First Nuclear
Equivalence
• What does this
diagram tell us?
Mechanisms of Development
• Second Cytoplasmic
specification
• What does this
diagram tell?
Mechanisms of Development
• Third Embryonic
induction
• What does this
diagram tell?
Chapter 9
Architectural Pattern
of an Animal
• Bilateria – Bilateral symmetry (2 sided)
• A bilateral animal has a dorsal (top) side
and a ventral (bottom) side, but also an
anterior (head) end and a posterior (tail)
end and a left and right side.
Hierarchical Organization of Animal Complexity
• 5 grades of hierarchical organization (Table 9.1)
– subcellular/protoplasmic (protozoans)
• unicellular animals
• organelles perform various func.
– cellular (sponges)
• aggregation of cells that are functionally differentiated
• division of labor but not associated w/ specific func.
– cell-tissue (jellyfish)
• aggregation of similar cells that perform common func. (epithelial,
etc.)
– tissue-organ (flatworms)
• assemblage of +1 tissues perform highly specialized func. (heart, etc.)
– organ system
• assemblage of organs work together
– skeletal, muscular, digestive, nervous, endocrine, immune,
reproductive, excretory, circulatory, respiratory, integumentary
Body Symmetry
• Symmetry = correspondence in size and shape
of parts on opposite sides of a median plane
– spherical symmetry = any plane passing through
center divides a body into mirrored halves
• round appearance, rare
– radial symmetry = parts of body are arranged
concentrically around oral/aboral axis, +2 plane
through oral/aboral axis results in mirrored halves
• tubular appearance, no front or back, sessile or free floating
• hydra, jellyfish, sea urchin, adult sea star (bilateral larvae)
• biradial symmetry = 2 planes can pass through oral/aboral axis to
produce mirrored halves
– comb jellies
• Radiata (Cnidaria, Ctenophora)
– not monophyletic group, arose separately
Body Symmetry
– bilateral symmetry = cut along sagittal plane
divides animal into 2 equal halves (left, right)
• better adapted for directional mvmt
• monophyletic group called Bilateria
• associated w/ cephalization (differentiation of head)
– well-suited for sensing/responding to environment
• terms associated w/ bilaterally symmetrical animals
– anterior = head end
– posterior = tail end
– dorsal = back side
– ventral = belly side
– medial = midline
– lateral = sides
Body Symmetry
–
–
–
–
–
distal = far from middle of body
proximal = near middle of body
frontal plane = divides body into dorsal and ventral halves
sagittal plane = divides body into right and left sides
transverse plane (a.k.a. cross section) = divides body into
anterior and posterior ends
– pectoral = chest region, area supported by forelegs
– pelvic = hip region, area supported
by hind legs
Body Cavities and Germ Layers
• Body cavity = internal space w/i body
– 2 cavities in most animals
– sponges have no body cavity
• Metazoan development
– zygote develops into blastula
• blastula = layer of cells surrounding blastocoel (fluid-filled cavity)
– blastocoel has no opening
– blastula develops into gastrula
• gastrula = 1 side of blastula forms depression,
which forms gastrocoel/archenteron (gut cavity)
– opening to depression = blastopore
» blastopore develops into mouth or anus
– lining of gut = endoderm, outer layer = ectoderm
– gastrocoel and blastocoel form 2 cavities
– blastocoel forms mesoderm in some sp.
• derived from endoderm
Mesoderm formation
Protostomes
Deuterostomes
Mesoderm Formation
• In protostomes (“first mouth”)
– Annelida/Arthropoda/Mollusca
– mesoderm forms from endodermal
cells near blastopore that migrate to blastocoel
– 3 body plans emerge after following initial mesoderm formation
• acoelomate = blastocoel fills w/ mesoderm cells, thus only gut cavity
– tissue btwn ecto- and endodermis filled by parenchyma cells
which are spongy and func. in food transport, waste disposal
• pseudocoelomate = mesoderm cells line outer edge of blastocoel,
thus 2 body cavities (pseudocoelom, gut cavity)
– pseudo b/c mesoderm partially surrounds cavity
• schizocoelous = blastocoel fills w/ mesoderm cells to form band of
tissue around gut, programmed cell death results in space w/i
mesodermal band, thus 2 body cavities (true coelom, gut cavity)
Mesoderm Formation
• In deuterostomes (“second mouth”)
– Echinodermata/Chordata/Hemichordata
– mesoderm forms from endodermal cells
in central portion of gut lining that
expand into blastocoel
– 1 body plan
• enterocoelous = mesodermal cells
expand outward to line blastocoel,
thus 2 body cavities (true coelom, gut cavity)
– result similar to schizocoelous plan
– cavities bound by mesoderm, lined w/ peritoneum
» peritoneum = thin membrane derived from mesoderm
that lines coelom
» mesenteries = suspend organs in coelom
Developmental Patterns
• Simplest developmental pattern (i.e. sponges)
– no distinct cleavage pattern
– embryos develop to blastula stage only
– blastula consists of 1 germ layer that reorganizes to form sponge
• aggregation of cells
• Diploblastic developmental pattern (i.e. sea anemones)
–
–
–
–
blastula develops into gastrula
develop 2 germ layers (ectoderm, endoderm)
develops tissues
typically radially symmetrical
• Triploblastic developmental pattern
–
–
–
–
develops 3rd germ layer (ectoderm, endoderm, mesoderm)
develops tissues
typically bilaterally symmetrical
blastula undergoes radial or spiral cleavage
Developmental Patterns
• Radial cleavage accompanied by following to become
deuterstomes (frogs, sea urchins)
– blastopore becomes anus
– coelom forms by enterocoely
– regulative cleavage of cytoplasm
• each blastomere (early cleavage cell) develops into normal larvae
• Spiral cleavage accompanied by following to become
protostomes (snails, segmented worms)
– blastopore becomes mouth
– mesoderm forms from 4d cell in embryo
• thus acoelomate, pseudocoelomate or coelomate
– mosiac cleavage of cytoplasm
• not all blastomeres develop into normal larvae
– lophotrochozoan (molluscs, annelids) vs. ecdysozoan protostomes
(arthropods, nematodes)
Diploblastic
No gastrula formation
Gastrula formation
Acoelomate
Protostome
Pseudocoelomate
Spiral
cleavage
Radial
cleavage
Schizocoelomate
Triploblastic
No cleavage
pattern
Lophotrochozoan
protostome
Deuterostome
Enterocoelomate
Ancestral unicellular organism
Unicellular
Multicellular
Aggregation of cells
Radial
Eumetazoan
Bilateral
Acoelomate
Pseudocoelomate
Schizocoelomate
Enterocoelomate
Body Plans of Major Taxa
• Unicellularity vs. multicellularity
– body forms diversify w/ advent of multicellular organisms
• Protozoans vs. mesozoans vs. metazoans
• Eumetazoans vary in symmetry, # body layers, gut structure
– some have blind/incomplete gut (1 opening)
– most have complete gut (entrance + exit) (tube w/i tube)
– some segmented (repitition of similar body segments along long.
axis)
• segment = metamere or somite
• ↑ mobility and structural complexity