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Intoranimal lecture 8
1. Animal are multicellular, heterotrophic eukaryotes with tissues that
develop from embryonic layers (with some exceptions)
• Several characteristics, taken together, sufficiently
define the group
– Heterotrophs
– Reproduce sexually, with the diploid stage usually
dominating the life cycle
– multicellular eukaryotes
– lack cell walls
– Their bodies are held together by structural proteins such as
collagen
– Nervous tissue and muscle tissue are unique, defining
characteristics of animals
– Tissues are group of cells that have a common structure,
function or both
2. Figure 32.2-1
Reproduction and Development
Zygote
Cleavage
Eight-cell
stage
After a sperm fertilizes an egg, the zygote undergoes rapid cell division called
cleavage
Cleavage leads to formation of a multicellular, hollow blastula
The blastula undergoes gastrulation, forming a gastrula with different layers of
embryonic tissues
5. More Animal Characteristics
• Many animals have at least one larval stage
i. A larva is sexually immature and morphologically
distinct from the adults
ii. A juvenile resembles an adult, but is not yet sexually
mature
• Most animals, and only animals, have Hox genes that
regulate the development of body form
i. Although the Hox family of genes has been highly
conserved, it can produce a wide diversity of animal
morphology
7. Animals can be characterized by
“body plans”
• Symmetry
– radial symmetry, with no front and back, or left or right
• Radial animals are often sessile or planktonic
– Two-sided symmetry is called bilateral symmetry
• Bilaterally symmetrical animals have
a dorsal (top) and a vental (bottom) side
A right and left side
Anterior (head) and posterior (tail) ends
Cephalization, the development of a head
9. Tissues
• Animal body plans also vary according to the
organization of the animal’s tissues
• Tissues are collections of specialized cells isolated
from other tissues by membranous layers
• During development, three germ layers give rise to
the tissues and organs of the animal embryo
1. Ectotherm is the germ layer covering the embryo’s surface
2. Endoderm is the innermost germ layer and lines the developing
digestive tube, called the archenteron
3. Mesoderm lies between the ectoderm and endoderm
10.
11. Body Cavities
• Sponges and a few other groups lack true tissues
• Diploblastic animals have ectoderm and endoderm
These include cnidarians and comb jellies
• Triploblastic animals also mesoderm; these include
all bilaterians
Most triploblastic animals possess a body cavity
A true body cavity is called a coelom and is derived
from mesoderm
– Coelomates are animals that possess a true coelom
• These include flatworms, arthropods, vertebrates and others
12. Figure 32.8
(a) Coelomate
Coelom
Digestive tract
(from endoderm)
Body covering
(from ectoderm)
Tissue layer
lining coelom
and suspending
internal organs
(from mesoderm)
(b) Pseudocoelomate
Body covering
(from ectoderm)
Pseudocoelom
Digestive tract
(from endoderm)
Muscle layer
(from
mesoderm)
A pseudocoelom is a
body cavity derived from
the mesoderm and
endoderm
(c) Acoelomate
Body covering
(from ectoderm) Tissuefilled region
(from
mesoderm)
Wall of digestive cavity
(from endoderm)
Triploblastic animals
that lack a body
cavity are called
acoelomates
13. Coeloms
• The coelom is a cavity entirely surrounded
by mesoderm.
• A coelom provides a tube-within-a-tube
arrangement which has many advantages:
Allows visceral organs to grow independently
of the body wall
Fluid-filled coelom acts as a hydrostatic
skeleton in some animals (e.g. earthworms)
In mammals, the pericardial, peritoneal, and
pleural cavities are formed from the coelom
14. Protostome and Deuterostome Development
• Based on early development, many animals can
be categorized as having protostome
development or deuterostome development
– In protostome development, cleavage is spiral and
determinate
– In deuterostome development, cleavage is radial and
indeterminate
– With indeterminate cleavage, each cell in the early
stages of cleavage retains the capacity to develop into a
complete embryo
– Indeterminate cleavage makes possible identical twins,
and embryonic stem cells
15. In some embryos, the daughter blastomeres are either above or to
the side of each other. This is said to be radial-type symmetry.
In some embryos, the daughter blastomeres are not direclty over
or beside each other. They are tilted to the left or right 45 degrees.
This latter cleavage symmetry is said to be spiral.
16. Figure 32.9
Protostome development
(examples: molluscs,
annelids)
(a) Cleavage
Deuterostome development
(examples: echinoderms,
chordates)
Eight-cell stage
Eight-cell stage
Spiral and determinate
(b) Coelom formation
Radial and indeterminate
Coelom
Archenteron
Coelom
Mesoderm
Blastopore
Blastopore
Solid masses of mesoderm
split and form coelom.
(c) Fate of the
blastopore
Mesoderm
Folds of archenteron
form coelom.
Anus
Mouth
Digestive tube
Key
Ectoderm
Mesoderm
Endoderm
Mouth
Mouth develops from blastopore.
Anus
Anus develops from blastopore.
17. New views of animal phylogeny are emerging
from molecular data
• Zoologists recognize about three dozen animal
phyla
• Phylogenies now combine morphological,
molecular, and fossil data
• Current debate in animal systematics has led to
the development of multiple hypotheses about the
relationships among animal groups
22. Points of Agreement
1. All animals share a common ancestor
2. Sponges are basal animals
3. Eumetazoa is a clade of animals
(eumetazoans) with true tissues
4. Most animal phyla belong to the clade Bilateria,
and some are bilarians
5. Chordates and some other phyla belong to the
clade Deuterostomia
23. Progress in Resolving Bilaterian
Relationships
• The morphology-based tree divides bilaterians into
two clades: deuterostomes and protostomes
• In contrast, recent molecular studies indicate three
bilaterian clades: Deuterostomia, Ecdysozoa, and
Lophotrochozoa
• Ecdysozoans shed their exoskeletons through a
process called ecdysis
24. Figure 33.2
Invertebrates are animals that lack a backbone that account
for 95% of known animal species
Porifera
ANCESTRAL
PROTIST
Lophotrochozoa
Bilateria
Eumetazoa
Common
ancestor of
all animals
Cnidaria
Ecdysozoa
Deuterostomia
25. Figure 33.3a
Porifera (5,500 species)
Placozoa (1 species)
0.5 mm
A sponge
Cnidaria (10,000 species)
A placozoan (LM)
Ctenophora (100 species)
A jelly
Acoela (400 species)
1.5 mm
Acoel flatworms (LM)
A ctenophore, or comb jelly
26. Figure 33.3b
Ectoprocta
(4,500 species)
Ectoprocts
A marine flatworm
Acanthocephala
(1,100 species)
Nemertea
(900 species)
Rotifera
(1,800 species)
0.1 mm
Platyhelminthes
(20,000 species)
Brachiopoda
(335 species)
A brachiopod
A rotifer (LM)
Annelida
(16,500 species)
Cycliophora
(1 species)
Curved
hooks
100 µm
An acanthocephalan (LM)
Mollusca
(93,000 species)
A ribbon worm
An octopus
A cycliophoran
(colorized SEM)
Lophotrochozoa
A marine annelid
27. Figure 33.3c
Loricifera (10 species)
Priapula (16 species)
Onychophora (110 species)
50 µm
A loriciferan (LM)
A priapulan
An onychophoran
Nematoda
(25,000 species)
Tardigrada
(800 species)
Arthropoda
(1,000,000 species)
100 µm
A roundworm
(colored SEM)
Ecdysozoa
Tardigrades
(colorized SEM)
A scorpion (an arachnid)
28. • 12.1. Advent of
Multicellularity
• A. Advantages
• 1. Nature’s experiments with
larger organisms without
cellular differentiation are
limited.
• 2. Increasing the size of a cell
causes problems of exchange;
multicellularity avoids
surface-to-mass problems.
• 3.cell assemblages in sponges
are distinct from other
metazoans, but molecular
evidence shows common
ancestry
29. •B. Form and Function
•1. Body openings consist of
small incurrent pores or ostia
and a few excurrent oscula.
•2. Openings are connected by
a system of canals; water
passes from ostia to osculum.
•3. Choanocytes or
flagellated collar cells line
some of the canals.
–a. They keep the current
flowing by beating of
flagella.
–b. They trap and
phagocytize food particles
passing by.
•4. The framework of the sponge is
composed of needle-like calcareous or
siliceous spicules or organic spongin
fibers.
30. Phylum Porifera
A.
General Features
•
Porifera means "pore-bearing"; their sac-like bodies
are perforated by many pores.
•
They are sessile and depend on water currents to
bring in food and oxygen and carry away wastes.
•
Their body is a mass of cells embedded in gelatinous
matrix and stiffened by spicules of calcium carbonate
or silica and collagen.
•
They have no organs or tissues; cells are somewhat
independent.
•
Being sessile, they have no nervous or sense organs
and have simplest of contractile elements
•
They are aside from the mainstream of animal
evolution and thus they are often called Parazoa
•
Most of the 5000 species are marine, about 150 are
freshwater
•
Morphology changes with substratum, calmness of
water etc…
•
Sponges are ancient (fossils extend to Cambrian
Period
31. Lophotochozoa
• The clade Lophotrochozoa was identified by
molecular data
• Some develop a lophophore for feeding,
others pass through a trochopore larval stage
and a few have neither feature
• Ex: flatworms, rotifers, ectopracts,
brachiopods, molluscs, annelids
32. Phylum Cnidaria
• Two forms – Polyp and medussa
Polyps = sessile
Medusa = free swimming
• Cnidocytes = stinging cells on tentacles carnivores
• Gastrovascular cavity = central body cavity
33. Phylum Platyhelminthes
• Flatworms
• Diffusion replaces body system
Gas exchange takes place across the
surface, and protonephridia regulate the
osmotic balance
• Reproduce asexually
by fission
• Reproduce sexually
by cross fertilization
• flukes and tapeworms
34. Phylum Nematoda
• Roundworms
• Some are parasitic
Hookworms = drink blood of GI tract
Trichirella found in pig muscle
Filarial roundworms infect lymphatic
system
35. Phylum Annelida
• Segmented worms
Closed circulatory system
Five pair of hearts
Pharynx draws in food
Crops store food
Gizzard grinds food
Intestine absorbs nutrients
Rest is passed through the anus
36. Phylum Arthropoda
• Dominant animals wrt numbers
– exoskeleton made of chitin
– efficient gas exchange
– Well developed sensory system
– Well developed nervous system
– Well developed circulatory system
37.
38. Phylum Mollusca
• Shells of calcium carbonate
– mantle lays down the shell
• Open circulatory system( except for
cephalopods)
• Radula tongue made of chitin used to
scrape for food
• Bivalve named for number of shells
• About three-quarters of all living
species of molluscs are gastropods
39.
40. Phylum Echinodermata
• Water-vascular system for locomotion,
respiration and food acquisition
• Lack circulatory system
• Have regenerative capabilities
Editor's Notes
Figure 32.2 Early embryonic development in animals.
Figure 32.2 Early embryonic development in animals.
Figure 32.2 Early embryonic development in animals.
Figure 32.3 Three lines of evidence that choanoflagellates are closely related to animals.
Figure 32.7 Body symmetry.
Figure 32.8 Body cavities of triploblastic animals.
Figure 32.9 A comparison of protostome and deuterostome development.
Figure 32.10 A view of animal phylogeny based mainly on morphological and developmental comparisons.
Figure 32.11 A view of animal phylogeny based mainly on molecular data.
