Study Guide Evolution of Animals Chapter – 19
Animalia – Fig 19.1 and Table 19.2 are important. I will ask questions on main animals in each phylum.
Concentrate on phylum characteristics or general characteristics of animals, protostomes, deuterstomes
and chordates.
1. Trends in evolution of animals a) Symmetry Fig 19.5 – sessile or slow moving animals had radial
symmetry (body parts arranged around a vertical axis) because food can come from any direction
but most animals evolved Bilateral Symmetry (body parts arranged on 2 sides of a vertical plane
because this favored in having a fixed anterior end b) Cephalization – Animals evolved head at
anterior end because when moving to search for food, shelter or mate they required maximum
information around them – this led to evolution of head having most sense organs to observe and
brain to process and finally also mouth to feed inside head itself c) Fig 19.8 Coelom is the space
between body organs =viscera and body wall (skin + muscles) lined by peritoneal membranes d)
Complete digestive system has mouth to feed and anus to defecate e) Segmentation is the internal
divisions of muscles, nervous tissue and excretory organs, also depicted externally in most animals.
2. Porifera = Sponges are the simplest animals. Fig 19.2. Sponges may have asymmetric or radial
symmetry. No true tissues or organs evolved in them. Epidermal cells line the surface Collar cells
establish water current and capture food with flagella. It is called Filter Feeding. Amoebocytes lie in
between the 2 layers and secrete Spicules – spine like skeletal structures formed of lime or silica or
sponging fibers. No nerve cells evolved yet.
3. Glass Sponges have spicules of silica and look like glass in a dead organism, found in deep water.
4. Cnidaria fig 19.3 (jelly fishes, corals) have a characteristic stinging cell nematoblast = cnidoblast.
Most of the times it paralyses the prey but may trap it. 2 main body layers with a jelly layer in
between. True tissues and organs evolved including the nerve cells. Incomplete digestive system and
radial symmetry is observed in cnidarians.
5. 2 Main Body Forms = Polyp and Medusa - Polyp – has a cylindrical body with a mouth and a ring of
tentacles armed with nematocysts surround the mouth. Incomplete digestive system because no
anus present. Mostly polyp is sessile and medusa is motile. Medusa has an umbrella like structure,
mouth is at the end of stick and tentacles cover the rim of umbrella. Fig 19.4
6. Physalia = Portugese man of war – has an air sac to float and has both specialized polyps and
medusa in the colony. It can trap preys like fish and others with its long tentacles.
7. Aurelia = Jelly fish has a large medusa, mouth is surrounded by 4 arms, 4 horse-shoe shaped gonads
having either eggs or sperms, can be seen through the bell. Polyp is reduced or absent in the life c
8. Sea Anemone = Metridium has advanced popyp with several rows of tentacles and gastrovascular
cavity divided by partitions.
9. Corals are advanced polyps, mostly colonial, and deposit lime around them and look like stone
having pores. When living each pore has a single individual formed of a polyp. Most corals harbor
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algae in them and can grow better in clear waters. Pollution of oceans is resulting in elimination of
corals from large areas of sea-beds.
10. Platyhelminthes = flat worms – Thin long bodies, bilateral symmetry, cephalization initiated,
incomplete digestive system with only mouth, space between internal organs and body wall filled =
Acoelomate, bisexual = monoecious animals.
11. Planaria – a member of free-living flat worms, head has 2 eye-spots, 2 auricles – lateral extensions
of head, mouth in the middle, branching gut (digestive system), slow moving bottom dwellers which
feed on small animals or dead animals. Fig 19.7
12. Parsitic flat worms include flukes and tapeworms.
13. Flukes are parasites living in the liver, intestines, lungs or blood vessels of vertebrates. Oral sucker
around mouth and ventral sucker on ventral side help fluke to attach host and feed on the tissues
and blood. Fresh water snail is an intermediate host in life cycle of most flukes.
14. Tape worm - It does not have any digestive system, absorbs food through body surface (is
absorptive instead of normal Ingestive mode of animals). It is very long, has a very tiny scolex with
hooks and suckers to attach to intestine.
15. Nematoda = Round worms – are amongst most widely distributed and most abundant animals
found everywhere including soils, water, marine or fresh, animal and plant tissues. You observed the
vinegar eels in undistilled vinegar and some are found in undistilled beer. Most round worms are
free living but many are human parasites – Ascaris. Fig 19.9
16. Complete digestive system – 1st to develop tube within tube body plant and a complete digestive
system. Pseudocoel – the false body cavity is present but is not lines by peritoneum membranes.
Parasitic round worms lack attaching organs like suckers or hooks found in parasitic flat worms.
Round worms are dioecious – sexes are separate, males are smaller and narrow and females are
longer and broader.
17. In Protostomes, Mouth (1st mouth) develops from blastopore. Fig 19.15. Protosomes include Flat
worms, Round worms, Rotifera, Mollusks, Annelids and Arthropods.
18. Phylum Mollusca has animals with soft body dorsally covered by a skin fold called Mantle and have a
single ventral foot. In majority of mollusks mantle secretes a shell. Most have a tongue like radula
with rasping teeth. Fig 19.10
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class
shell
Feed on
Foot
gastropods
Conical spiral
Most on plants/algae
Extensible muscular
bivalves
2 similar hinged parts
Planktons, filter feeder
Hatchet like, used for burrowing
Body parts
Head, tentacles,
radula, jaws
snails
No head or tentacles or radula
cephalopods
Mostly reduced
predators
Divided into arms / tentacles
fixed on head
Head, radula, eyes,
Clams, oysters, scallops
Squids, octopus, nautillus
example
19. Phylum Annelida includes segmented animals with coelom the true body cavity. Annelids have well
developed digestive, circulatory, nervous and reproductive systems. But use skin as the respiratory
system. Some of them have external gills. They have stiff bristles called setae or chaetae for locomotion. Fig 19.11
class
Locomote with
Live in
Feed on
character
Sexes
Neries (polychaetes)
parapodia
Marine water
Small animals, trap
planktons
Tentacles on head
separate
Earthworms (oligochates)
setae
Burrowing in land
Organic matter rich soil
Leeches (Hirudinea)
Oral and posterior sucker
Water or land
Blood, are ectoparasites
Permanent clitellum
bisexual
Temporary clitellum
bisexual
20. Phylum Arthropoda has animals with exoskeleton of hard plates of chitin and jointed appendages.
These are the largest group of animals and were 1st to colonize land. Most have a respiratory system
of cuticular tubes called Trachea which directly carry oxygen to the tissues. Fig 19.13-14
class
Antenna
Body regions
Walking legs
Live in
Respiration by
example
crustaceans
2 pairs
Cephalothorax
and abdomen
5 pairs
arachnids
absent
Cephalothorax
And abdomen
4 pairs
insects
1 pair
Head, thorax
and abdomen
3 pairs
water
gills
Cray fish, crab,
lobster, shrimp
On land
Book-lungs
Spiders,
scorpion, mites
On land
trachea
Butterfly,
wasp, beetles,
Bugs, flies
millipedes
1 pair
Head, thorax
and abdomen
2 pair/
segments
On land
trachea
Cylindrical
body
centipedes
1 pair
Head and long
body
1 pair /
segment
On land
trachea
Flat body
21. In Deuterostomes Anus (2nd mouth) develops from the blastopore. Deuterostome animals have 2
major animal Phyla – Echinoderms and Chordates.
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22. Echinoderm (spiny-skinned) – a) radial symmetry in adult but bilateral larva b) bone like
endoskeleton or test c) water vascular system of canals and tube-feet for locomotion and capturing
food d) regenerate broken arms and other body parts. Fig 19.16
23. Sea Stars – have 5 thick arms with viscera extended into them and feed on Clams or Oysters.
24. Brittle Stars – have 5 thin arms without viscera. The arms show snake like movements and get easily
broken but help them swim.
25. Sea Urchins – have very large spines coming out of test and possess Aristotle’s Lantern a feeding
device to eat sea weeds or kelps. No arms are present
26. Sea Cucumbers – have cylindrical body and pick food with their tentacles or are filter feeders. No
arms present.
27. Feather Stars – have branched 5 arms and remain attached most of the time but can swim freely
when needed.
28. Chordates possess 4 characters at least once during their life time (in embryo or larva or adult):
a) Notochord – an elastic chord, is replaced by vertebrae in most chordates called Vertebrates
b) Dorsal and hollow nerve tube – develops into brain and spinal cord in vertebrates
c) Pharyngeal Gill Clefts or pouches – are slit like openings in sides of pharynx and help in
respiration in lower chordates.
d) Post-anal Tail – is present in all chordates.
Urochordate – Sea Squirt
Notochord and nerve tube in
tail of larva. Uro = tail
Body covered by test with
spicules. No head or eyes.
Fixed to sea rocks
Filter feeder
Fig 19.17
Cephalochordate – Amphioxus
Notochord extends into
anterior end. Cephalo = head
Fish like body has no head.
Burrowed or free swimming
Filter feeder
Fig 19.18
Vertebrates –fish mammal
Notochord of embryo or larva
replaced by vertebrae
Distinct head, eyes, fins or
limbs
Free swimming
Mostly Predators or herbivores
Fig 19.20
29. Vertebrates have jawless fishes Cyclostomes or Agnatha and Gnathostomates the vertebrates with
jaws in mouth.
30. Agnatha – Cyclostomes are jawless fishes only having unpaired fins. The circular mouth act as a
sucker a rasping tongue helps in feeding. Lamprey is an ectoparasite of sharks. Hag fish is slimy and
usually enters dead or dying animals and feeds on the soft viscera. Cyclostomes lack jaws and paired
fins/limbs of other vertebrates.
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31. Gnathostomates include fishes – animals with paired fins and Tetrapods – animals with 2 pairs of
limbs. Fishes live in water, respire with gills, skin covered with scales, have 2 chambered heart both
paired and unpaired fins. Fishes have 2 main classes Cartilaginous fishes and Bony fishes.
Fish Class 
Position of mouth
Pharyngeal gill-slits
Scales
Tail fin
Swim bladder – to
regulate buoyancy
For example
Chondrichthyes=cartilaginous fishes
Ventral, below the snout
Exposed and easily seen
Indistinct, small
Lobes asymmetrical
absent
Sharks, rays, Fig 19.21
Osteichthyes = bony fishes
terminal
Covered by gill cover
Distinct, large
Lobes symmetrical or unlobed
Present in many fishes, helps to gain
or lose depth in water
Salmon, Tuna, gold fish, Fig 19.22
32. Amphibians (amphi = both, bios = living, can breathe in air as well as water) are naked vertebrates
lacking scales/feathers / hair. They use skin as respiratory organ and developed lungs. Amphibians
moved freely on land but have to return to water to release eggs. Fertilization is external and eggs
hatch to form larva. The larva is the 1st feeding stage and is fish like having gills. It undergoes
metamorphosis to become adult amphibian. Frog  Egg tadpole larva  Frog. For example Frogs,
Toads, Salamanders, mud puppies.
Class 
Fishes
Amphibians
Reptiles
Aves = birds
Mammals
Skin cover
scales
absent
scales
feathers
hair
heart
2 chambered
3 chambered
3 chambers
4 chambered
4 chambered
Respiration by
gills
Skin, lungs
lungs
lungs
lungs
2 pairs of
fins
legs
legs
legs
legs
Teeth used for
Holding food
holding
holding
Absent replaced
by bill or beak
Chewing food
ears
absent
Ear drum at
skin level
Ear drum in
Ear canal
Ear drum in Ear
canal
Pinna outside
ear canal
Eggs
Need water
Need water
Laid on land
Laid on land
Give birth
33. Reptiles developed the amniotic egg and became 1st true land vertebrates. Amnion is a fluid filled
sac and protects embryo from desiccation (drying up) on land. This eliminated the need of external
water, like amphibians, for fertilization. They have scales on skin to prevent water loss, and also
have claws on digits and a 3-chambered heart. Eggs with lot of yolk and hatch into adults. No larval
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stage present. Reptiles include turtles, lizards, snakes, alligators and crocodiles. Dinosaurs, the most
famous extinct animals, belonged to reptiles. Birds evolved as a direct line from dinosaurs.
34. Birds are endotherms and maintain high body temperature and can live in extreme cold climates
like Antarctica. The bones are very light but strong. Body has feathers and wings. Feet are covered
with scales to indicate close relationship to reptiles. Birds also lay amniotic eggs with large yolk and
no larva needed. Due to marked parental care for the eggs and hatchlings most birds lay only 2-3
eggs. The evolution of beak or bill helped them to specialize for different kinds of food. Sternum
developed a high flat vertical bone, keel, to accommodate bulky flight muscles. Lungs are supported
by air sacs to get oxygen even during expiration (breathing out). Due to brilliance of colors Huxley
called them ‘Glorified Reptiles’.
35. Mammals – body covered by hair, mammary glands to feed milk, specialized teeth (incisiors for
cutting; canines for tearing; premolars and molars for chewing), ear canal covered with Pinna, 7
vertebrae in neck.
36. Mammals include egg laying mammals, marsupials and placental mammals.
37. Monotremes = the egg laying (Oviparous) mammal – live only in Australia, lay eggs and feed
hatchlings with milk. Duck bill platypus and spiny ant eater are only 2 examples. They are the
connecting link between early reptiles and mammals.
38. Marsupials live only in Australian and South American regions. They give birth Viviparous) to
premature babies and many carry them in an abdominal pouch = marsupium. Mammary glands are
present in the pouch. Well known examples are Kangaroo, Koala and Opossum.
39. Placental Mammals – are most successful and most evolved animals including humans. Give birth
(viviparous) to mature babies. Endotherms – maintain body temperature. Most live on land. Aquatic
mammals include Whales, dolphins, seals etc and flying mammals are bats. In viviparous animals
developing embryo draws nutrition and oxygen from mother’s blood and pass out wastes to it. Bear
is omnivore but lion, tiger, wolf, cat and dog are carnivore mammals. Cattle, deer, zebra , giraffe are
grazing animals. Monkeys, apes and humans are primate mammals.
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