Chapter 25

Chapter 25
A Summary
AP Biology
Spring 2011
Vertebrate chordates:
mammals, birds, reptiles,
amphibians, jawed fishes,
jawless fishes
Invertebrate chordates:
tunicates , lancelets
Vertebrates: 4500, 8600,
7000, 4900, 21000, 84
Invertebrates: 2100
Sea stars, sea urchins
Crabs, spiders, insects
1,113,000 (recent
estimates of 10’s of
Pinworms, hookworms
Snails, slugs, octopuses
Leeches, earthworms,
Turbellarians, flukes,
Jellyfish, hydra
Trichoplax adhaerens
Animals: multicelled heterotrophs that
ingest other organisms or some portion of
Tissues are arranged into organs and organ
Most motile at some stage of their life cycle
They reproduce sexually, and in some cases
asexually, or both
Embryos develop through a series of stages
Animal Origins
Variation in Animal Body Plans
◦ Organization:
◦ All animals are multicellular and show an
internal division of labor
◦ A key innovation for animals was development
of tissues
◦ Tissue development starts in the embryo
Specialized Cells, Tissues, Organs
Cell: the basic unit of all forms of life
◦ A neuron is a cell
Tissue: group of similar cells that
performs a particular function
◦ Sciatic nerve is a tissue
Organ: group of tissues that work
together to perform related functions
◦ Brain is a organ
Specialized Cells, Tissues, Organs
Tissue Development
◦ Outer ectoderm is the tissue giving rise to the
epithelium that lines the body surfaces and
forms other organs, and in some species,
serves as an external skeleton (ex. Insect
◦ Endoderm develops into the gut lining and
connective tissues serving as the structural
material for an internal skeleton
◦ Third tissue layer forms between the other two,
mesoderm, which is the source of muscles
and other organs in all animals more complex
than jellyfishes
Germ Layers
Germ Layers
Diploblastic: animals with only 2 cell
layers, their bodies consist of ectoderm
and endoderm, and mesoglea (middle
glue) holds two layers together
◦ Porifera and cnidarians
Triploblastic: having 3 true cell layers
◦ Complex animal phyla
Germ Layers
Bilateral Symmetry: body is organized
along a longitudinal axis with right and
left sides that mirror each other
◦ Most are triploblastic
◦ Occurs in humans, lobsters
Radial Symmetry: any cut through the
central axis of the organism would
produce mirror images
◦ Occurs in jellies
Body Symmetry
Cephalization: concentration of sensory
equipment at one end (usually the
anterior, or head end) of the organism
Development of Head
Coelomates: posses a body cavity filled
with fluid, and this space separates an
animal’s digestive tract from the outer
body wall
◦ A true coelom forms from tissue derived from
◦ Most complex: Annelida, Mollusca, Arthropoda,
Body Plans
Pseudocoelomates: are triploblastic
animals with a cavity formed from the
blastocoel, rather than the mesoderm
◦ Nematodes or roundworms
Acoelomates: have no cavities between
their alimentary canal and the outer wall
of their bodies
◦ Flatworms
Body Plans
Coelom: fluid filled body cavity that is
completely surrounded by mesoderm
◦ Represents advance in course of animal
evolution because it provides a space for
elaborate organ systems
◦ Like digestive tract or cardiovascular system
Body Plans
From the Primitive
To the Complex
No symmetry or radial symmetry
Bilateral symmetry
No head
Head with sensory apparatus
Mesoglea holds two cell layers
3 cell layers, including mesoderm
Pseudocoelomate or coelomate
No true tissue
True tissues, organs, and organ
Little specialization
Much specialization
Be familiar with 9 common phyla and
representative animals of each
 For each animal phyla: think in terms of
strategies that animals have evolved to
adapt to particular environments and
notice the trends of development from
simple to complex
Characteristics of Animals
No symmetry
Have no nerve of muscle tissues
Sessile- do not move
Filter nutrients from water drawn into a
central cavity
Consist of two cell layers only: ectoderm
and endoderm connected by noncellular
Porifera: Sponges
Have specialized cells but no true tissues
or organs, each cell carriers out many
 Evolved from colonial organisms
◦ If you squeeze a sponge through fine
cheesecloth it will separate into individual cells
that will spontaneously reaggregate into a
Reproduce asexually by fragmentation
Also reproduce sexually: hermaphrodites
Porifera: Sponges
Radial symmetry
 Body plan is polyp (vase shaped), which
is mostly sessile, or medusa (upside
down bowl shaped), which is mostly
Cnidarians: Hydra and Jellyfish
Life cycle: some go through a planula
larva (free swimming) stage then go
through two reproductive stages
◦ Asexually reproducing (polyp)
◦ Sexually reproducing (medusa)
Cnidarians: Hydra and Jellyfish
Two cell layers only: ectoderm and
endoderm connected by noncellular
 Have a gastrovascular cavity where
extracellular digestion occurs
 Carry out intracellular digestion inside
body cells in lysosomes
Cnidarians: Hydra and Jellyfish
Have no transport system because every
cell is in direct contact with the
 All members have stinging cellscnidoctes
◦ Containing stingers, which are called
Ex. Hydra
Cnidarians: Hydra and Jellyfish
Simplest animals with:
◦ Bilateral symmetry
◦ An anterior end and three distinct cel layers
(ectoderm, endoderm, mesoderm)
Platyhelminthes: Flatworms,
Digestive cavity has only one opening for
both ingestion and egestion so food cannot
be processed continuously
Have solid body and no room for true
digestive or respiratory systems to circulate
food or oxygen
Flatworms have solved this problem in a
unique way
They body is so flat and thin that many body
cells can exchange nutrients and wastes by
diffusion with the environment
Platyhelminthes: Flatworms,
Unsegmented worms with bilateral
symmetry but little sensory apparatus
 Many are parasitic
◦ Trichinella causes trichinosis, contracted by
eating uncooked pork
C. elegans: widely used as an animal
model in studying genes and embryonic
Nematodes: Roundworms
C. elegans
Platyhelminthes: Flatworms,
Bilateral symmetry with little sensory
 Digestive tract is a tube-within-a-tube
consisting of crop, gizzard, and intestine
 Nephridia for excretion of nitrogen
wastes, urea
 Closed circulatory system: heart consists
of 5 pairs of aortic arches
Annelids: Segmented Worms
(earthworms, leeches)
Blood contains hemoglobin and carries
 Diffusion of oxygen and carbon dioxide
through moist skin
 Hermaphrodites
Annelids: Segmented Worms
(earthworms, leeches)
Have soft body often produced by a hard
calcium-containing shell
 Open circulatory system with blood-filled
spaces called hemocoels or sinuses
Mollusks: Squids, Octopuses,
Slugs, Clams, and Snails
Have bilateral symmetry with 3 body
◦ Head-foot: contains both sensory and motor
◦ Visceral mass: contains the organs of
digestion, excretion, and reproduction
◦ Mantle: specialized tissue that surrounds the
visceral mass and secretes the shell
Mollusks: Squids, Octopuses,
Slugs, Clams, and Snails
Radula: movable, tooth-bearing
structure, acts like a tongue
 Most have gills and nephridia
Mollusks: Squids, Octopuses,
Slugs, Clams, and Snails
Jointed appendages
 Segmented into head, thorax, abdomen
 More sensory apparatus than in annelids
◦ Gives them more speed and freedom of
Chitinous exoskeleton protects animal and
aids in movement
Arthropods: Insecta
(grasshopper), Crustacea (shrimp,
crab), Arachnida (spider)
Open circulatory system with a tubular
heart and hemocoels, sinuses
 Malpighian tubules for removal of
nitrogenous wastes, uric acid
 Air ducts called trachea bring air from the
environment into hemocoels
Arthropods: Insecta
(grasshopper), Crustacea (shrimp,
crab), Arachnida (spider)
Most are sessile or slow moving
 They have bilateral symmetry as an
embryo but revert to the primitive radial
symmetry as an adult
 The radial anatomy of the adult is an
adaptation to a sedentary lifestyle
Echinoderms: Sea Stars (Starfish)
and Sea Urchins
Their water vascular system creates
hydrostatic support for the tube feet, the
locomotive structures
 Reproduce by sexual reproduction with
external fertilization
Echinoderms: Sea Stars (Starfish)
and Sea Urchins
Can reproduce by fragmentation and
◦ Any piece of a sea star that contains part of the
central nervous canal will form a completely
new organism
Have endoskeleton consisting of calcium
◦ Endoskeleton grows with the body
◦ Exoskeleton does not and must be shed
Echinoderms: Sea Stars (Starfish)
and Sea Urchins
Two subphyla of invertebrate chordates
 Simpler versions of vertebrates
Chordates: Tunicates, Lancelets
Many of 4 anatomical features that
characterize chordates appear only during
embryonic development
◦ Notochord: long, flexible rod that appears
during embryonic development between the
digestive tube and the dorsal nerve cord
◦ Dorsal, hollow nerve cord: formed from a plate
of ectoderm that rolls into a hollow tube
Chordates: Tunicates, Lancelets
◦ Pharyngeal clefts: grooves that separate a
series of pouches along the sides of the
pharynx; in most chordates the clefts develop
into slits that allow water to enter and exit he
mouth without going through the digestive
◦ A muscular tail posterior to the anus
Chordates: Tunicates, Lancelets
Have a notochord: rod that extends the
length of the body and serves as a flexible
Have a dorsal, hollow nerve cord
The tail aids in movement and balance
Coccyx bone in humans is a vestige of a
Chordates: Fish, Amphibians,
Reptiles, Birds, Mammals
Birds and mammals are hemeotherms
◦ Maintain a consistent body temperature
◦ All other chordates: fish, amphibians, and
 Cold blooded although some reptiles are
endotherms (heat from within) and are able to
raise their body temperature
Chordates: Fish, Amphibians,
Reptiles, Birds, Mammals

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