Evolution of Animals
• Fossil record of invertebrates is incomplete
because soft-bodied animals are poorly preserved
as fossils.
• All animals probably evolved from Protists.
• The classification of animals is based on the level
of organization or number of germ layers,
symmetry, type of coelom, body plan, and
presence or absence of segmentation.
• The following evolutionary tree is based on these
features and shows a possible evolutionary
relationship between the animals.
Evolutionary tree
Levels of Organization
• Three levels or organization: cell, tissue, or
organ
• One of the main events during animal
development is the establishment of germ
layers.
• If two germ layers (ectoderm and endoderm)
are present, then the animal has the tissue level
of organization.
• If all three germ layers (ectoderm, endoderm,
and mesoderm) are present, then the animals
has the organ level of organization.
Type of Body Plan
• Two body plans are present in the animal
kingdom:
• Sac plan:
• Incomplete digestive system with only one
opening.
• Ex: Jellyfish
& planaria
•Tube-within-a-tube plan:
•Complete digestive system.
•Two openings allows for specialization
along the length of the tube.
•Ex: Roundworms, earthworms, insects
Type of Symmetry
• Animals can be asymmetrical, radially
symmetrical, or bilaterally symmetrical.
• Asymmetrical animals have no particular
symmetry.
• Radial symmetry means the animal is
organized similar to a wheel.
• Bilateral symmetry means the animal has
definite right and left halves.
• Bilateral symmetry leads to cephalization
(brain and sense organs located an anterior
end of animal).
Type of Coelom
• A true coelom (in coelomates) is an internal body
cavity completely lined with mesoderm, where
internal organs are found. Benefits:
• Allows organs to freely move, grow, and
develop independently of the body wall
• Fluid cushions and protects organs from shocks
– in some acts as a skeleton
• Allows for separation of digestion & circulation
• Allows for increase in size & metabolic rate.
• Coelomates are either protostomes or
deuterostomes (explained a few slides later).
• Ex: Annelids, mollusks, arthropods
•Animals that have a pseudocoelom have a body
cavity incompletely lined with mesoderm.
•No circulatory system – fluid in
pseudocoelom transports oxygen & nutrients
•Pressure of fluid inside also provides support
as would a skeleton
•More mobile, more complex reproductive &
digestive systems.
•They can store wastes for discharge out of
the body.
•Ex: Roundworms, rotifers
•Acoelomates have mesoderm but no body cavity.
•Movement squeezes & distorts the body,
restricting the flow of nutrients and other
materials
•Have no circulatory system. Must rely either on
diffusion or on muscle contractions for the
transport of nutrients, respiratory gases, and
waste products around the body. (Less efficient
than heart & blood vessels which develop in
those with a coelom.)
•Ex: Flatworms, sponges, jellyfish
Protostomes vs. Deuterostomes
•During development, when the embryo resembles
a tiny globe of cells, a small pucker develops on
one side of the embryo.
•This grows into a pocket, and allows some cells
to migrate inside to form an additional layer of
cells within the outer layer.
•In the Protostomes, the mouth develops from the
edge of this pocket; the anal opening develops
later.
•In the Deuterostomes, the reverse is true; the
pocket edge develops into the anus, and the mouth
is formed later.
Segmentation
• Segmentation is the repetition of body parts
along the length of the body.
• Animals can be segmented or nonsegmented.
• Segmentation leads to specialization of parts
because the various segments can become
differentiated for specific purposes.
• Ex: annelids, arthropods, and chordates
(includes vertebrates).
•
•
•
•
•
•
Phylum Porifera - Sponges
Meaning: Pore-bearing
Symmetry – none (asymmetrical)
Organization – cellular level
Acoelomates – no body cavity (so no
organs)
Non-segmented
Habitat – fresh & salt water
• Anatomy (see below and diagram page given
separately)
Anatomy
•Epidermis – found along outer body wall
•Amoeboid cells (amebocytes) – middle layer
•Transport nutrients
•Produce spicules
•Form sex cells
•Collar cells - inner layer – digest nutrients
•Collar cells contain the following:
•Flagella - pull water in through pores and
circulate water though the sponge
•Filaments - trap food particles.
•
•
•
•
Life processes
Sponges are classified according to type of
spicules
Support - spicules (act like bones for the
sponge)
Diet - filter feeders – filter bacteria, protists,
and sometimes small crustaceans
Feeding –
– Filaments trap food
– Collar cells digest food (engulf food particles
(endocytosis), digest them, and pass them to
amoeboid cells.
•Movement:
- Swim as larva
- Sessile (permanently attached to a
surface) as adults.
•Response - no nervous system.
•Excretion - through the osculum.
•Respiration - take in oxygen as water passes
through body – diffusion.
•Internal transport - ameboid cells transport
nutrients around the body from cell to cell
•Reproduction –
•Hermaphrodites (make eggs & sperm).
•Asexually by:
•Budding: Produce internal buds called
gemmules (cells containing ameboid
cells, organic molecules, & spicules) that
can grow into new sponges when the
conditions are more favorable
•Regeneration: Growth of a whole
organism from a fragment
•Sexually:
•Release sperm into the water
•Sperm enters pores of another sponge of
same species
•Fertilizes egg within
•Larva released through osculum
•(see life cycle diagram – separate sheet).
•Some will release eggs & sperm into internal
cavity, larva develops, and is released into
water.
•Poor reproductive odds!!!
http://www.eeob.iastate.edu/faculty/DrewesC/htdocs/Q-sponge.htm
Phylum Cnidaria
•Named for – specialized stinging cells called
cnidocytes (contain the stingers called
nematocysts – these may contain poison)
•Symmetry – radial
•Organization – have endoderm & ectoderm tissue level
•Acoelomates – no body cavity (so no organs)
•Non-segmented; sac body plan
•Habitat – mostly salt water, hydra found in fresh
water
•Body forms: may be a polyp or a medusa, or
may alternate between the two forms.
•Polyp – tentacles up, usually sessile
•Medusa – tentacles down, usually active
•Examples of animals –
•Sea anemone – solitary polyp, very colorful
•Coral – some solitary, most colonial, polyp
form, calcium carbonate skeleton, form reefs
•Portuguese man-of-war – colony of polyp &
medusa individuals, each with specialized
jobs such as feeding & reproduction
•Jellyfish – medusa, can live at great depths
•Hydra – freshwater, polyp form, commonly
attached to underwater rocks or plants, less
than 1cm in length
•Sac body plan – single opening serves as
mouth and anus
•Outer tissue layer – epidermis
•Inner tissue layer – gastrodermis
•Mesoglea – jelly-like material that
separates above 2 tissue layers
•Circular & longitudinal muscle fibers
•Tentacles surround mouth
•Large space inside called gastrovascular
cavity
Life processes
•Movement:
•Directional
•Move by contraction & expansion of
body
•Tentacles can grab prey
•Response:
•Nerve net – interconnecting nerve cells
communicate with sensory cells
throughout body
•Support
•Hydrostatic skeleton –fluid-filled closed
chambers; internal pressures generated by
muscle contractions cause movement as
well as maintain the shape of the animals
•Diet – protists and small animals
•Feeding –
•Sting prey with nematocysts
•Stuff food into mouth using tentacles
•Don’t chase their prey – but movement of
medusa can help drawn food in towards
body.
•Food passes into GVC (gastrovascular
cavity)
•Digestion – cells of gastrodermis take in food
through endocytosis and digest the food in
their vacuoles.
•Internal transport:
•Nutrients and oxygen pass from cell to
cell through the process of diffusion
•Respiration:
•Diffusion between epidermal cells and
exterior watery environment, and
between gastrodermal cells and fluid
within GVC
•Excretion:
•Wastes are excreted through the mouth
•Reproduction:
•Usually appear as separate males & females
•Sexual reproduction – see life cycle diagram
given separately
•Jellyfish –
•Release eggs & sperm into water
•Swim as larva, settle as polyps, then
divide to become medusa
•Several young from one fertilized egg
•Hydra – release egg or sperm from body
wall; meet, swim as larva, settle as polyp
•Asexual reproduction
•Budding – cluster of cells form, break off ,
grow into adults
•Regeneration – fragments develop into new
animals
Phylum Platyhelminthes
•Meaning – flatworms
•Symmetry - bilateral
•Sac body plan; non-segmented; acoelomates.
•Organization - 3 germ layers – endoderm,
ectoderm, & mesoderm – organ level
•Have organs for all life processes except
respiration and circulation
•Habitat – fresh or salt water, moist environments,
inside host
•Examples:
Tapeworms
Marine flatworms
Flukes
Freshwater planarians
Planarians • Lifestyle - free-living
• Habitat - freshwater
• Movement – secrete slime, push through with
cilia, muscles
• Excretion – flame cells – interconnecting canals
throughout body
• Response - small brain
- ladder of nerves
- light-sensitive eyespots
- Auricles sensitive to chemicals
(all located in the head - cephalization).
Planarian
•Diet – plankton (small worms or crustaceans)
•Feeding – wrap around prey
- secrete slime
- extend pharynx –
sucking motion tears
up and swallows food
•Digestion – occurs in GVC
•Respiration and internal transport - Flattened
body allows for diffusion of oxygen &
nutrients from cell to cell
•Gender - hermaphrodites
•Sexual reproduction – cross-fertilization,
have sex, exchange sperm, each planaria gets
pregnant - 2 sets of young hatch from eggs 2-3
weeks later.
•Asexual reproduction – capable of regeneration;
1 worm can even grow 2 heads or 2 tails!!
Parasitic Flatworms
• Two classes - flukes and tapeworms
• Require host to carry on life cycle – see next slide
• Primary host – infect as adult
• Secondary host – infect as larval stage
• Tapeworm –
• Anterior scolex with hooks and suckers to hold
itself inside the gut.
• No digestive system; absorbs host’s digested
food through skin
• Special enzymes counteract host’s digestive
enzymes
•Body is an assembly line of square sections
called proglottids, which contain male and
female sex organs.
•As proglottids mature, they break off, pass
with feces, and release eggs.
•When animals feed in feces-contaminated
food, eggs hatch inside, and larva eventually
form cysts in muscles of secondary host.
•When humans eat infected meat, larva hatch
from cyst, attach to intestine, and grow to
adulthood.
Life cycle:
•Contracted by eating undercooked, infected
beef, pork, or fish.
•Transmitted to cats & dogs by fleas that have
eaten feces of infected host
•Primary symptom – weight loss
•In prolonged infections – worms migrate to
eyes, heart, brain, lungs, & liver & form cysts –
cause swelling, cramps, diarrhea, anemia, &
seizures
•Diagnosed by fecal exam; treated with medicine
Fluke
•Have sucker at anterior end to attach to host
•Various species – can infect digestive tract, bile
duct, blood, & lungs.
•Blood flukes cause schistosomiasis – one of the
most common worm infections worldwide
(about 200 million in mostly Middle East, Asia,
Africa, & S. America)
•Common in areas with poor sewage treatment
•Enter through skin when in infected water – see
life cycle diagram next slide
Schistosomiasis
•Diagosed by fecal exam; treated with
medicine
•Symptoms: nausea, abdominal pain,
increased bowel movements, diarrhea, weight
loss, fatigue
•Burrow through host, feed on host’s blood &
tissues.
•Can live for up to 2-3 decades inside host
(usually only 5-10 years)
•Reproduce non-stop – 100 – 300 eggs/day
Phylum Nematoda (Roundworms)
•Non-segmented
•Bilateral symmetry
•Organization - 3 germ layers – endoderm,
ectoderm, & mesoderm – organ level
•Pseudocoelomates (body cavity) – filled with fluid
– space for organs
•Tube-within-a-tube body plan – complete digestive
tract with mouth and anus.
•Habitat – fresh or salt water, soil, inside host (both
plants & animals)
Life Processes
•Internal transport - fluid in pseudocoelom
transports nutrients & oxygen
•Support – fluid in pseudocoelom provides
support (hydrostatic skeleton).
•Respiration - Breathe through their skin diffusion.
•Movement - longitudinal muscles – move
with whiplike motion – inefficient in water,
good in soil & host.
•Excretion – waste is removed through the
anus
•Feeding & digestion –
•Feed using muscular pharynx which
shoots out from mouth
•Food is digested in intestine
•Gender - appear as separate males &
females
•Sexual reproduction – male injects sperm
into female, she lays eggs.
Roundworm anatomy
Types of
nematodes:
• Ascaris
• Contracted
when one
eats
vegetables
contaminated
with human
waste.
• Trichina
worm:
• Trichinosis
is contracted
when eating
undercooked
pork
containing
encysted
larvae.
•Filaria worm:
•Carried by
mosquitoes
and causes
elephantiasis
by blocking
lymphatic
drainage.
•Pinworms:
•Common
infections in
children.
•Hookworm:
•Once common
in the southern
United States.
•Person
becomes
infected when
walking in soil
contaminated
with human
waste
•Guinea worm:
•Person
becomes
infected when
drinking water
with water fleas
contaminated
with guinea
worm eggs.
•Worm emerges
from leg once
fully grown.
Phylum Annelida (segmented worms)
• Symmetry - bilateral
• Organization - 3 germ layers – organ level
• Coelomates -have a body cavity – more
complex organs
• Tube-within-a-tube body plan – specialized
organs in digestive tract
• Segmented both externally, and internally by
partitions called septa.
• Habitat – fresh or salt water, soil
• Support - a hydrostatic skeleton
• Movement - move by alternating contraction of
longitudinal and circular muscles found in each
segment.
– Partitioning of the coelom permits each body
segment to move independently.
• Respiration - breathe through their skin.
• Internal transport - closed circulatory system
with blood vessels that run the length of the body
and branch to every segment.
•Excretion - nephridia (tiny tubules found in
each segment) remove nitrogen waste through
openings in body wall; anus removes waste
from digested food.
•Response - a brain connected to a ventral solid
nerve cord with ganglia in each segment.
•Three classes –
•Polychaeta – marine worms
•Oligochaeta – earthworms
•Hirudinea - leeches
Marine Worms
• Have paddle-like appendages at the side of each
segment called parapodia.
– Add surface area for respiration
• Found in bundles on the parapodia - bristles that
anchor the worm called setae.
• Only have functional sex organs during breeding
seasons.
• During breeding seasons, some worms form sex
organs in special segments and shed these segment
during breeding. Eggs or sperm within float to
surface where fertilization takes place – hatch as
larva.
Lifestyles of these worms vary:
•Sessile tube worms that filter feed with tentacles
•Clam worm is a predator with powerful jaws, & a
defined head region with eyes & sense organs.
Earthworm, Lumbricus
Earthworms
• Head is not well-developed; no parapodia.
• Have pairs of setae in each segment; when
muscles contract in each segment, setae anchor
in the soil, and aid locomotion.
• Most scavenge for food in the soil – feed on
leaves & decaying matter
• Digestion: Mouth  Pharynx (swallows food)
 Esophagus (connects pharynx & crop) 
Crop (stores food)  Gizzard (grinds food –
contains small stones swallowed by the worm)
 Intestine (digests food)
•Internal transport - Five “hearts” (aortic arches)
pump blood and a branch blood vessel reaches
each segment.
•Gender - These worms are hermaphroditic.
•Reproduction
•Meet at clitellum, which secretes a ring of
mucus
•Each injects sperm into mucus
•Tube slides forward, picking up eggs
•Tube slides off body & is left behind
•Fertilization occurs within tube
•Worms hatch in a few weeks – no larval stage
• Segmentation in earthworms is evidenced by:
– Body rings
– Coelom divided by septa
– Setae on most segments
– Ganglia and lateral nerves in each segment
– Nephridia in most segments
– Longitudinal and circular muscles in each
segment
– Branch blood vessels in each segment
Leeches
• Most in fresh water, some in soil or salt water.
• No setae; 2 suckers (1 small anterior, 1 large
posterior) to feed.
• Some are free-living predators; most are fluid
feeders that attach themselves to open wounds.
• Bloodsuckers cut through tissue with 3 saw-like
jaws – leaves “Y” – shaped wound.
• Anesthetic in saliva prevents victim from feeling
attack and dilates blood vessels; anticoagulant
(hirudin) in their saliva keeps blood from clotting;
pouches in crop allows for storage of up to 5 times
their weight – long time between feedings.
•
•
•
•
•
•
•
Phylum Mollusca
Meaning – soft-body
Coelomates (reduced in some)
Symmetry – bilateral
Organization – organ level
Tube-within-a-tube body plan
No segmentation
Found in fresh or salt water, and on land
Molluscan diversity
• 3 distinct parts to all mollusk bodies:
– Visceral mass – soft-bodied part
containing organs
– Foot – muscular part used for
movement
– Mantle – membrane covering
visceral mass; in some molluscs, it
secretes the shell
• Molluscan groups are distinguished by
a modification of the foot.
•Gastropods – (stomach-foot) the foot is
ventrally flattened.
•Ex: slugs & snails
•Muscle contractions along foot move
the animal
•Some species have a shell
•Some species live on land – mantle also
functions as a lung by moving air in &
out through respiratory pores
•Radula – tongue with teeth to scrape up
food
• Cephalopods - the foot has evolved into tentacles
about the head; ex: squid & octopus
• Cephalization - brain and nerves; camera-type
eye; scent; pigments in skin to change colors
• Move rapidly by jet propulsion
• Feed using beak and radula
• Have a closed circulatory system.
• Escape predators by secretion from ink gland
• No shell; hydrostatic skeleton; cartilage around
brain
• Sperm transferred to female in “dart;” she lays
and guards eggs – no larval form
• Bivalves
– Ex: clams, oyster, scallops & mussels
– A coelom is present but reduced
– Support - Two shells held together by muscles
– Respiration - using gills hanging on both sides
of visceral mass
– Movement - have a hatchet-shaped foot – in
some species, this can allow for movement –
most are sessile
– Response - no cephalization - 3 pairs of
ganglia connected by nerves control body.
• Internal transport – heart pumps blood into an
aorta, then through sinuses rather than blood
vessels (open circulatory system).
• Feeding - filter feeding.
– Water enters by an incurrent siphon; exits by
excurrent siphon.
– Food trapped on the gills is swept toward
the mouth.
• Digestion - mouth with labial palps (helps
bring food to mouth), an esophagus, a
stomach, and an intestine.
•Excretion - 2 kidneys remove waste from cavity
around heart; food waste passes through anus,
which empties at an excurrent siphon.
•Reproduction:
•Sexes are usually separate
•A single gonad (either ovary or testis) is
located around the coils of the intestine.
•Some clams release both eggs & sperm into
water
•Other species release sperm only into water,
enters female, and fertilizes egg at gills.
Phylum Echinodermata
• Habitat – salt water
• Examples: Sea lilies, feather stars, sea
cucumbers, brittle stars, sea urchins, sand
dollars, & sea stars
• Symmetry – radial as adult, larva is a freeswimming filter feeder with bilateral
symmetry.
• Organization – organ level
• Coelomates; non-segmented
• Don’t really fit either tube or sac body plans
Echinoderm diversity
Sea Stars
• Support - endoskeleton consisting of spine-bearing,
calcium-rich plates; spines protrude through skin.
• Movement - water vascular system
– Water enters this system through the sieve plate
(aka madreporite), passes into a stone canal, then
to the ring canal, into radial canal, then into
ampullae, and into tube feet; expansion and
contraction of tube feet move the sea star along.
• Internal transport - fluid in body cavity & water
vascular system
– Cilia lining the peritoneum move fluid through coelom to
transport nutrients & oxygen.
• Respiration – Gas exchange occurs across skin
gills and tube feet
• Excretion - waste diffuses through fluid in coelom
& body wall; food waste passes through anus
• Feeding and digestion –
– Eat bivalves (2-shelled mollusks)
– Everts its cardiac stomach inside the shells and
secretes enzymes; partially digested food is
taken in.
– Digestion continues in pyloric stomach with
enzymes made in digestive glands in each arm
•Response –
•Central nerve ring with radial nerves in each arm
•Sensory tube feet at end of each arm to “taste”
the water
•Photosensitive eyespot at the end of each arm
•Reproduction – gonads in each arm – open directly
to outside
•Asexually - by regeneration – 1 small piece can
grow into a new sea star
•Sexually - by releasing eggs & sperm into water
Sea star anatomy
Arthropods
•
•
•
•
•
•
Meaning – “jointed foot”
Symmetry – bilateral
Coelomates – complex internal organs
Tube-within-a-tube body plan
Segmented
The most varied and numerous of animals (over
1 million identified, probably 30 million really
exist!!)
• Five Classes – Crustaceans, Insects, Arachnids,
Millipedes, & Centipedes
•Successful because of:
•Flexible exoskeleton for support (made of
chitin, offers protection, muscles attach to it,
locomotion, and retains moisture); shed
exoskeleton (molt) during growth
•Jointed appendages
•Segmented; specialization of body regions (3
body regions – head, thorax, and abdomen –
with specialized appendages in each region)
•A well-developed nervous system (brain, nerve
cord, eyes, & antenna)
•Small size; high reproductive rate
•Live in water, land and air
Arthropod diversity
•
•
•
•
•
Crustaceans
Mostly marine; crayfish, shrimp, crab, lobster
Response: compound eyes, 2 pair of antennae,
brain, & ventral nerve cord.
Feeding: specialized mouth parts.
Digestion: stomach – 2 regions – 1 to grind food, 1
to filter coarse particles & prevent them from
entering digestive glands where digestion takes
place.
Locomotion: 5 pairs of walking legs include a first
pair of pinching claws (called chelipeds).
• End of abdomen has uropod & telson used to
help crayfish move backwards.
• In the crayfish, head and thorax are fused into
a cephalothorax which is covered on the top
and sides by a carapace.
• Internal transport - The crayfish has an open
circulatory system - heart pumps blood into a
hemocoel consisting of sinuses where the
hemolymph flows about the organs.
• Respiration takes place by gills under the hard
carapace.
• Excretion - Green glands – excrete metabolic
wastes through duct; food waste passes out
through anus
•Reproduction - the abdominal segments have
swimmerets, which are used to hold the eggs in
the female.
•Sexes are separate in the crayfish; can tell
male from female by looking at first pair of
swimmerets – point upward in male
•Swimmerets - transfer sperm to female.
Male crayfish, Cambarus
Insects
• Many exhibit social behavior, such as bees or ants.
• Response: in addition to brain & nerve cord, head
usually bears a pair of antennae, compound eyes,
simple eyes, and in some tympanum for the
reception of sound waves.
• Locomotion: thorax bears three pairs of legs and
up to 2 pairs of wings.
• Excretion - Malpighian tubules collect nitrogen
waste, which is added to digestive tract; waste
then passes out through anus.
Insect diversity
• Internal transport: open circulatory system;
heart pumps hemolymph into aorta that
leads to a hemocoel (contains sinuses),
where it circulates before returning to the
heart.
• Feeding: mouthparts specialized for diet –
for ex. chewing vegetation, siphoning
nectar.
• Digestion: mouthparts chew food, crop
stores, digestion occurs in stomach &
intestine.
•Some insects, such as grasshoppers, are
adapted to a terrestrial life:
•Respiration - tracheae (small tubules);
open to outside by holes called
spiracles (on abdomen)
•Have wings that allow them to evade
enemies
•Third pair of legs is suitable for
jumping.
• Reproduction:
• Mate by having sex
• Female grasshopper has ovipositor at posterior
end to dig hole and lay eggs.
• Grasshoppers undergo gradual metamorphosis
from nymph to adult (referred to as incomplete
metamorphosis).
• Butterflies undergo complete metamorphosis,
changing from larva to pupa to adult.
Female grasshopper
Arachnids
• Include terrestrial spiders, scorpions, ticks, and
mites.
• Ticks and mites are parasitic
• 2 body segments – cephalothorax & abdomen
• The cephalothorax bears six pairs of
appendages: the chelicerae and the pedipalps,
and four pairs of walking legs.
• Chelicerae contain fangs to deliver poison
• Pedipalps sense or hold the prey
• Spiders are well-adapted to life on land:
• Excretion - have Malphigian tubules – they
secrete uric acid, helping to conserve water.
• Respiration - using a “book lung” – inner
body wall folds inward to look like pages of
book.
• Spiders spin silk used in various ways.
• Where spiders spin webs, the type of web is a
feature that demonstrates the evolutionary
relationship among spiders.
• Response - 8 simple eyes and no antennae
Arachnid diversity
Centipedes
•Head and numerous body segments
•1 pair of legs per segment (about 30 legs)
•Breathe with trachea
•Carnivores; nocturnal; move quickly
•Poison claws to paralyze prey
Millipedes
•Head and numerous body segments
•2 pairs of legs per segment (about 70 legs)
•Breathe with trachea
•Herbivores, move slowly, harmless to
humans