Download Animal Evolution –The Invertebrates

Animal Evolution –The
Invertebrates
Chapter 25 Part 1
Impacts, Issues
Old Genes, New Drugs
 Humans and other vertebrates share genes with
invertebrates, including the cone snail – which
makes powerful conotoxins
25.1 Animal Traits and Body Plans
 Animals
• Multicelled heterotrophs that move about during
part or all of the life cycle
• Body cells do not have a wall and are typically
diploid
• The overwhelming majority are invertebrates
Animal Body Plans: Organization
 Tissues
• Cells of a particular type and function, organized
in a specific pattern
 Tissue formation begins in an embryo
• Ectoderm and endoderm
• Mesoderm
Tissue Formation
 Formation of a three-layer animal embryo
ectoderm
mesoderm
endoderm
Fig. 25-2, p. 404
Animal Body Plans: Body Symmetry
 Body Symmetry
• Simplest animals are asymmetrical (sponges)
• Jellyfish and hydras have radial symmetry
• Most animals have bilateral symmetry
 Cephalization
• In most bilateral animals, nerve cells are
concentrated at the head end
Body Symmetry
Fig. 25-3, p. 405
Animal Body Plans: Gut and Body Cavity
 Gut
• Digestive sac (incomplete digestive system) or
tube (complete) that opens at the body surface
 Typically, a body cavity surrounds the gut
• Coelom: Cavity lined by mesodermal tissue
• Pseudocoel: Cavity is partially lined
 Acoelomates have no body cavity
Body Cavities
Fig. 25-4a, p. 405
epidermis
A No coelom
(acoelomate animal)
gut
cavity
organs packed between
gut and body wall
Fig. 25-4a, p. 405
Fig. 25-4b, p. 405
epidermis
B Pseudocoel
(pseudocoelomate animal)
gut
cavity
unlined body cavity around gut
Fig. 25-4b, p. 405
Fig. 25-4c, p. 405
epidermis
C Coelom
(coelomate animal)
gut
cavity
body cavity with a lining (dark
blue) derived from mesoderm
Fig. 25-4c, p. 405
Animation: Types of body cavities
Two Lineages of Bilateral Animals
 Protostomes
• First opening in the embryo becomes the mouth
• Second opening becomes the anus
 Deuterostomes
• First opening in the embryo becomes the anus
• Second opening becomes the mouth
Animal Body Plans: Circulation
 In small animals, gases and nutrients diffuse
through the body
 Most animals have a circulatory system
• Closed circulatory system: Heart pumps blood
through a continuous vessel system
• Open circulatory system: Blood leaves the
vessels
Animal Body Plans: Segmentation
 Many bilateral animals are segmented
• Similar units repeated along length of body
• Repetition allows evolution of specialization
Variation in Animal Body Plans
25.2 Animal Origins
and Adaptive Radiation
 Fossils and gene comparisons among modern
species provide insights into how animals arose
and diversified
Becoming Multicellular
 Animals probably evolved from a colonial,
choanoflagellate-like protist
 Choanoflagellates (“collared flagellate”)
• Modern protists most closely related to animals
• A collar of microvilli surrounds the flagellum
• Have proteins similar to adhesion or intercellular
signaling proteins in animals
Choanoflagellates
Fig. 25-5a, p. 406
Fig. 25-5b, p. 406
Fig. 25-5c, p. 406
amoebozoans
fungi
choanoflagellates
animals
Fig. 25-5c, p. 406
A Great Adaptive Radiation
 Animals underwent a dramatic adaptive
radiation during the Cambrian
Relationships and Classification
 Animals have traditionally been classified based
on morphology and developmental pattern
• Mainly features of body cavities
 A newer system puts all animals with a threelayer embryo into protostomes or deuterostomes
• Protostomes are divided into animals that molt
(Ecdysozoa) and don’t molt (Lophotrochozoa)
Relationships and Classification
Relationships and Classification
chordates
echinoderms
arthropods
tardigrades
annelids
mollusks
Deuterostomes
Protostomes
Coelomate animals
rotifers
Pseudocoelomate animals
roundworms
flatworms
Acoelomate animals
Animals with a 3-layer embryo
cnidarians
sponges
placozoans
Animals with tissues
Animals
Fig. 25-7a, p. 407
Deuterostomes
chordates
echinoderms
arthropods
tardigrades
Ecdysozoa
roundworms
Protostomes
rotifers
mollusks Lophotrochozoa
annelids
flatworms
Animals with a 3-layer embryo
cnidarians
sponges
placozoans
Animals with tissues
Animals
Fig. 25-7b, p. 407
25.1-25.2 Key Concepts
Introducing the Animals
 Animals are multicelled heterotrophs that
actively move about during all or part of the life
cycle
 Early animals were small and structurally simple
 Their descendants evolved a more complex
structure and greater integration among
specialized parts
25.3 The Simplest Living Animal
 Placozoans, the simplest known animals, have
no body symmetry, no tissues, and just four
different types of cells
• Example: Trichoplax adherens
25.4 The Sponges
 Sponges are simple but successful; they have
survived in seas since Precambrian times
 Sponges (phylum Porifera)
•
•
•
•
Attach to seafloor or other surfaces
No symmetry, tissues, or organs
Pores with flagellated collar cells filter water
Sexual or asexual reproduction
Sponges
Fig. 25-9a, p. 409
Fig. 25-9b, p. 409
Fig. 25-9c, p. 409
Fig. 25-9d, p. 409
Sponge Body Plan
water out
glassy
structural
elements
amoeboid
cell
pore
semifluid
matrix
flattened
surface
cells
central
cavity
collar cell
water in
water
in
flagellum collar of microvilli
nucleus
Fig. 25-10, p. 409
Sponge Reproduction and Dispersal
 Hermaphrodite
• Individual that produces both eggs and sperm
• Sperm are released into water; eggs are retained
• Zygote develops into ciliated larva
 Larva
• Free-living, sexually immature stage in life cycle
• Settles and develops into adult
Sponge Characteristics
 Toxins and fibrous or sharp body parts deter
predators
 Some freshwater sponges survive unfavorable
conditions by producing gemmules
 Sponges show cell adhesion, self-recognition
25.5 Cnidarians—True Tissues
 Cnidarians (phylum Cnidaria)
• Radial animals with two tissue layers
• Medusae (jellyfishes) are bell shaped and drift
• Polyps (sea anemones) are tubular with one end
usually attached to a surface
 Four classes: hydrozoans, anthozoans,
cubozoans, and scyphozoans
Two Cnidarian Body Plans
outer epithelium
(epidermis)
gastrovascular
cavity
mesoglea
(matrix)
inner epithelium
(gastrodermis)
gastrovascular
cavity
Fig. 25-11, p. 410
Animation: Cnidarian body plans
Cnidarian Diversity
General Cnidarian Features
 Nematocysts
• Stinging organelles in tentacle cells, triggered by
contact, used in feeding or defense
 Nerve net
• Simple nervous system of interconnecting nerve
cells extending through the tissues
 Hydrostatic skeleton
• Fluid-filled structure moved by contractile cells
Nematocyst Action
lid
nematocyst
(capsule at
free surface of
epidermal cell)
capsule's
trigger
(modified
cilium)
barbs on
discharged
thread
exposed
barbed
thread in
capsule
Fig. 25-12, p. 410
Animation: Nematocyst action
Cnidarian Life Cycle
Fig. 25-13a, p. 411
Fig. 25-13 (b-d), p. 411
reproductive
polyp
male medusa
female medusa
ovum
sperm
zygote
feeding
polyp
one branch of a colony
growth of a polyp
ciliated bilateral larva
Fig. 25-13 (b-d), p. 411
D Medusae form at the tips
of specialized polyps and
are released.
reproductive
polyp female medusa
ovum
sperm
zygote
feeding
polyp
C A larva grows into a polyp
that reproduces asexually
by budding, thus forming a
colony.
male
medusa
growth of
a polyp
ciliated
bilateral
larva
A Medusae are the
sexual stage in this
species. They are
diploid and form
eggs and sperm by
meiosis.
B Fertilization produces
a zygote that develops
into a bilateral, ciliated
larva called a planula.
Stepped Art
Fig. 25-13, p. 411
Animation: Cnidarian life cycle
25.3-25.5 Key Concepts
The Structurally Simple Invertebrates
 Placozoans and sponges have no body
symmetry or tissues
 The radially symmetrical cnidarians such as
jellyfish have two tissue layers and unique
stinging cells used in feeding and in defense
between protostomes and
deuterostomes
Animation: Early frog development
Animation: Types of body symmetry