Lecture 8: Animals

What is an animal?
Multicellular eukaryotes
Chemoheterotrophs- digest food inside
body
Sexual reproduction
Muscles and nerves

Animal Ancestry
Colonial flagellate hypothesis
Ancestor was colony of flagellates in a sphere > cells
became specialized > infolding created two layers of
cells
Supported by fact that many tissues develop this
way embryonically
Supported by implication that radial symmetry
preceeded bilateral symmetry
Supported by choanoflagellates- closest protist
relative of animals

Colonial Flagellate
• This is an illustration of
Proterospongia. The cells
are embedded in a jelly-
like matrix. Whether this
is a colonial
choanoflagellate or a very
simple animal depends
upon whom you ask.

Evolution
Many kinds arose during Cambrian
explosion, happened so fast the origin of
many is murky
DNA evidence points to the tree we
currently use
See pg. 312

Terms Used for Classification
Germ layer: tissue layers found in embryos;
develop into different tissue types
Endoderm: Innermost germ layer- gives rise
to lining of digestive tract, etc.
Ectoderm: Outermost germ layer- gives rise
to nervous system and outer integument
Mesoderm: Middle germ layer- gives rise to
many organs, muscle, connective tissue

Terms Used for Classification
Radial symmetry: organized circularly
Bilateral symmetry: left- right
symmetry (like us)
Cephalization: localization of brain and
sensory organs

Terms Used for Classification
Protosomes: the first embryonic opening
becomes the mouth
Deuterosomes: the first embryonic
opening becomes the anus
Coelom: Body cavity where the organs
are located

Terms Used for Classification
Acoelomates: do not have a coelom
Pseudocoelomates: have a partial coelom
Coelomates: have a true coelom
Segmentation: repetition of body parts
along the length of the body

Classification
Animals are classified based on the
characteristics we just listed
We will now examine different groups

Sponges
Phylum Poriphera
Base of evolutionary tree of animals - collar cells at pores
are basically identical to choanoflagellates
Cellular level organization
Multicellular, but lack organized tissues
Filter feeders, can filter huge amounts of water per day
Can reproduce both sexually and asexually
Asexually: budding
Sexually: eggs and sperm released into central cavity

Cnidarians
Phylum Cnidaria, sea anemones and
jellyfish
Have radial symmetry
Have two germ layers: ecto and endoderm
Capture prey with tentacles that have
stinging cells
Have tissue level of organization

Flatworms
Phylum Platyhelmenthes
Bilateral symmetry
Have all 3 germ layers
Acoelomates
Have cephalization- small brain, eyespots,
chemosensitive organs
Captures food by wrapping it up and covering it
in mucus, then tearing and sucking up

More flatworms
Digestive tract only has one opening
Hemaphrodites; sexual reproduction
Free living are called planarians
Parasitic are tapeworms and flukes
Have hooks and suckers on mouth to
hold onto host tissues
Can live for years

Roundworms
Phylum Nematoda
Have a body cavity- Pseudocoelomates, because not
completely surrounded by mesoderm
Complete digestive tract- open on both ends
Nonsegmented
Many are free living and live in a variety of habitats
and eat a variety of food
Many parasites as well: roundworm, hookworm,
Elephantiasis, Trichinosis

Hookworms and the
American South
People in the South after the Civil War seen as
lazy
Study of people and hygiene habits
Trees instead of latrines used
Hookworms! Can travel up to 6’ after being
deposited- were causing large infections
Just digging a hole that was 6’ deep solved the
problem

Molluscs
Phylum Mollusca, snails, octopuses, scallops, clams,
nautiluses
Have a coelom, proteosomes
Have 3 parts:
Visceral mass: contains organs
Foot: used for locomotion
Mantle: covers the visceral mass- may secrete
exoskeleton to form shell
Also may have a radula: like a toothy tongue

Molluscs
There are 3 types of molluscs:gastropods,
cephalopods, bivalves
Gastropods: Conchs, snails, nudibranchs
Foot ventrally flattened, muscle
contractions pass along the foot to move it
Terrestrial snails use the mantle as a
lung

Molluscs
Cephalopods: Octopus, Squid, Nautilus
“Head-footed” - the foot is the tentacles around
the head
Have a beak- use tentacles to seize prey and
beak and radula to tear it up
Complex nervous and sensory systems
Can move quickly by jetting water out of the
mantle

Molluscs
Bivalves: Clams, oysters, scallops,
mussels
Shell has two parts, foot projects
ventrally from shell
Filter feeders, water enters through a
siphon and food adheres to the gills; food
then moved to the mouth by cillia

Annelids
Phylum Annelida, worms
Has coelom and are segmented, proteosomes
Coelom is filled with fluid; it is divided by septa which make
it more rigid- facilitates movement
Complete digestive tract; have crop, gizzard, intestine,
accessory glands, etc.
Circulatory system to carry blood
Have a brain
Remove waste by nephridia- ducts that carry waste to pores
in the skin

Annelids
Again, 3 main groups: Polychaetes, oligochaetes,
leeches
Divided by how many setae (=bristles) on each
body segment- these bristles anchor the worm and
help it move
Polychaetes: have many setae, are predatory
Oligochaetes: Have a few- decomposers that live in
soil: earthworms
leeches: No setae - have suckers to attach to food

Polychaetes

Oligochaetes
Giant earthworm!

Leeches

Arthropods
Phylum Arthropoda: Over one million species! Insects, crustaceans,
arachnids
Coelom, segmented, proteosomes
Have six characteristics:
1. Jointed appendages- hollow tubes moved by muscles
2. Exoskeleton- made of chitin, rigid and jointed
3. Segmentation- Some repeated, some fused in to head, abdomen
and thorax only
4. Well-developed nervous system- Brain and ventral nerve cord,
eyes, many other senses
5. Variety of respiratory organs- Gills, book lungs, or trachae, also
open circulatory system
6. Metamorphosis- reduces competition of various age classes

Arthropods
Crustaceans: lobsters, crabs, barnacles, shrimp
Mostly marine, but also freshwater (crayfish) and
terrestrial (pillbugs)
Head has 5 pairs of appendages: antennae,
antennules- sensory, 3 mouthparts
Thorax has 5 pairs of walking legs, first is the claw
Abdomen has swimmerets- like small paddles and
tail
Hugely important in food chain - krill, etc

Arthropods
Arachnids: Spiders, scorpions, ticks, mites,
harvestmen
Spiders- Have cephalothorax and abdomen, kill
prey with venom, use silk
Scorpions- oldest terrestrial arthropods, nocturnal
Ticks- are parasitic
Horseshoe crabs- grouped with arachnids, but very
unique in many ways

Arthropods
Insects: Largest group of animals
Have head, thorax, and abdomen
Can have wings- one or two pairs
Live in huge variety of environments
and eat huge variety of food

Echinoderms
Phylum Echinodermata: sea stars, sea urchins,
sea cucumbers
Deuterosomes; bilaterally sym. as larvae but
radially sym. as adult
No head, brain or segmentation
No advanced nervous or circulatory system
These seem so primitive, why discuss them here?
They are closely related to Chordates!

Chordates
Phylum Chordata: Fish, amphibians, reptiles, mammals
Coelom, deuterosomes, segmented
4 characteristics:
1. Notochord: Dorsal supporting rod
2. Dorsal tubular nerve cord: contains a tube filled with fluid
3. Pharyngeal pouches: in many, seen only in the embryo-
become gills in larval amphibians and fish, in humans
become auditory tubes, tonsils, thymus and parathyroids
4. Tail: A postanal tail

Chordates
Most chordates are vertebrates, in which the
notochord has been replaced by the vertebrae
(backbones) which protect the nerve cord
(spinal cord)
However, there are a few chordates that are
invertebrates: the Tunicates and the
Lancelets
Marine organisms- sea squirts

Vertebrates
Series of evolutionary advances used to
characterize the verts-
See evolutionary tree on pg. 325 for a
list of these advances

Here, Fishy, Fishy, Fishy
Jawless fish: the first vertebrates
No jaws- they are cylindrical, do not have
paired fins- they undulate through the
water
Two groups today: hagfish and lampreys-
they have a circular mouth
Jaws are thought to have evolved from the
first pair of gill arches

Fish- Sharks!
Sharks, rays and skates are
Cartilaginous fish, they have a skeleton
made of cartilage instead of bones
Great predators: they can sense electrical
currents, pressure changes, and have a
great sense of smell

FISH
Bony fish: most numerous and diverse, two types:
Ray-finned: Like trout, perch, etc., very diverse
group
Have swim bladder to control buoyancy, skin
covered by bony scales
Respire by having water flow through the
mouth over the gills
Single circuit circulatory system- Heart
pumps blood to gills and then directly to body

FISH
Lobe-finned: Have fleshy fins
Ancestors of amphibians
Most have lung- so can breathe air

Amphibians
Frogs, toads, salamanders, cecilians
Have jointed limbs so can walk on land, also
eyelids to keep eye moist, ears, larynx, larger brain
Need water to reproduce
Most have lungs, also respire through skin
3 chambered heart, blood from body and lungs is
sent out to body and lungs
Most show metamorphosis

Reptiles
Dinos, snakes, lizards, turtles, crocs, birds
Body covered in scales
3 chambered heart
Can reproduce on land without water- amniote
egg- provides embryo with food, water and
oxygen, protects it from drying
Except for birds (and some dinos?) are
ectothermic- body temp controlled by environment

Birds
Really, birds are reptiles- feathers are just
modified scales
However, some differences- egg is hard instead of
leathery, endothermic
Flying- many many adaptations to allow flight
Hollow bones, front legs are wings
4 chambered heart
Well-developed brains, good vision

Mammals
Mammals have mammary glands that produce milk for
offspring, and hair
First mammals were monotremes and marsupials-
monotremes lay eggs, marsupials have pouch
Placental mammals evolved later, but are most diverse
group today
Embryo develops inside uterus, maternal blood
provides nutrients and oxygen
It is the same membranes that do this in the egg that
do this in the uterus- what the afterbirth is
Mammals have big brains and are very active

Humans
Humans are Primates- includes
monkeys, apes and humans
This does not mean monkeys
apes humans
Rather, it means that all primates
share a common ancestor

Primates
Primates primarily adapted to arboreal life-
limbs are mobile, have 5 digits, have
opposable thumb and frequently big toe
Trend is towards larger and more complex
brain
Humans most closely related to African
apes- chimps, gorillas
last common ancestor ~ 7 MYA

Hominids
Humans, apes and human-like
ancestors are the hominids
Can stand erect and walk on two feet
We will discuss some human ancestors

Hominids
Early fossils, around 7 MYA, the time
of the ape- hominid split:
Sahelanthropus tchadensis: opening
for spine suggests bipedalism,
smaller canines
Ardipithicus ramidus: 4 MYA, teeth less
apelike, only fragments found so far

Hominids
Australopithecines- group of hominids
that diversified in Africa about 4 MYA
A. afarensis- Lucy- stood upright,
bipedal, but small brain (3.18 MYA)
One of these species may be the direct
ancestor of humans

Hominids
Homo habilis- ~2 MYA, larger brain, used
tools, smaller teeth
skulls seem to indicate that the speech
centers of the brain were enlarged- could
probably communicate and co-operate to
gather food
Co-operation may have led to H. habilis
out-competing the Australopithecines

Hominids
Homo erectus- 1.9- 0.3 MYA, fossils found in
Africa, but also Asia and Europe
Probably several species included in this
group
Still larger skulls, flatter face, taller
Fossils found in many sites- were able to
travel long distances
First to use fire, made advanced tools

Hominids
Homo neandertalensis- 200,000 YO, found in
Germany
Short, stocky, heavy build, prominent brow
Culturally advanced- lived in caves, may
have made houses, made many tools
Hunted large animals
Buried their dead

Hominids
Cro-Magnons- oldest fossils to be
designated as our species, Homo sapiens
Fossils from France
Compound tools, great hunters
Had language, lived in groups
Had art- cave drawings

Hominids
Homo sapiens- how did first humans evolve?
We’re not sure- there are two theories:
Out of Africa: H. sapiens evolved in Africa, migrated
to Europe and Asia and replaced hominids already
there
Multiregional continuity hypothesis: evolved
independently in several regions
In the MCH- different regions would be genetically
dissimilar, OOA would be more genetically alike
Thus far it seems that the OOA is the most
supported