The document summarizes the reproductive systems of major animal phyla. Most reproduce sexually with internal or external fertilization, while some can also reproduce asexually through budding, fragmentation, or other means. Reproductive structures and strategies vary widely between phyla from broadcast spawning of gametes to live birth of offspring. The evolution of the amniotic egg allowed for protected development on land in reptiles, birds, and mammals.

1. Animal Reproduction
Systems

2. Phylum Porifera

3. Sexual:
Sperm are broadcast into the
water column
Choanocytes take in sperm and
transport it to an egg in the
sponge’s mesohyl
The zygote then develops within
the mesohyl OR is expelled into
the water column and develops
there
Most species are hermaphroditic

4. Asexual:
Fragmentation:
When individual pieces
of sponge that are free
floating in the water
column come together
to form a sponge
themselves
Budding:
Sponges can grow buds
that become detached
and form sponges
themselves
Gemmules:
Internal buds surrounded by
spongin and spicules that
allow sponges to survive in
harsh conditions; when parent
sponge dies, gemmule
develops into a new sponge
when conditions are favorable

5. Phylum Cnidaria

6. Class Hydrozoa
Hydras, Portuguese Man-of-War
Polyp Medussa
Colonies are dioecious—separate sexes
Reproductive polyps, gonozooids , bud off
medussa
The medussa then produce egg and sperm
that are released into the water column
where the zygote forms and become free
swimming or settle on a substrate
asexual sexual
Dioecious
Reproductive parts are called gonozooids,
which are sacs containing either ovaries or
testes
Fertilization occurs externally when the men
of war shed their gametes into the open
ocean; sperm from one colony fuses with
the eggs of another colony

7. Class Scyphozoa Class Cubozoa
In sexual reproduction
cnidarians alternate
between polyp and medusa
form
A mature polyp will absorb
its tentacles and split
horizontally into many
juvenile medussae
When mature, the medussa
will release gametes into
the water where the zygote
forms
Asexual reproduction
consists of budding when
the jelly is in polyp form

8. Class Anthozoa corals, sea anemones
Broadcast Spawning species release egg and
sperm into the water column on
environmental cue
Zygotes develop into larvae that attach to a
substrate and develop into mature polyps
and colonies
Brooding Species release only sperm into
the water column while eggs are retained
in the mature polyp
zygotes form within the adult and then
released into the water column to attach
to a substrate
Asexual forms of reproduction are regeneration and fragmentation of corals

9. Phylum Platyhelminthes

10. Class Turbellaria
Planarians
Class
Trematoda
Flukes
Class Cestoda
tapeworms

11. SEXUAL:most animals are hermaphrodites
In planarians sperm are transferred to individuals; when sperm
is deposited that animal accepts the role as female and vise
versa.
Marine flatworms: penis fencing
In flukes and tapeworms, there are multiple stages in a life cycle
including host, secondary host, and so on.
Internal fertilization
Because they are hermaphroditic, they have evolved methods
that prevent self-fertilization (ex. Eggs develop and different
times than sperm)

12. ASEXUAL:
Planarians can regenerate after fragmentation
They can also bud or split down the middle or across

13. P h y l u m
A n n e l I d a

14. Class Oligochaeta
eathworms
Class Hirudinea
leeches
Class Polychaeta
polychaets like
“clam worms”

15. S e x u a lSome can produce entirely
sexual or sexual during part
of the year and asexual
another
Many are hermaphroditic
In earthworms, a pair will
line up and exchange sperm
by shedding a mucousy tube
produced by the clitellum
Fertilization takes place
externally after mucousy
tube dries out forming a
coccoon

16. A s e x u a l
Some species
reproduce asexually by
budding or dividing
into two or more
pieces
Annelids, except for
leeches, can
regenerate after
fragmentation or
damage
Budding

17. Phylum Mollusca

18. Class Gastropoda
Class Polyplacophora
Class Bivalvia
Class Cephalopoda
Reproduction will vary because of the abundant amount of species in Mollusca
Bivalves exhibit external fertilization. Both sperm and egg are released into the water
column . After fertilization, larvae develop which undergo metamorphoses into adult
form.
Cephalopods have separate sexes. Males will use a modified tentacle to place sperm into
the mantel of a female. Females will either care for fertilized eggs or release them.

19. Phylum Nematoda

20. Nematodes usually reproduce
sexually
Females may contain over 27
milllion eggs and lay over 200,000
a day
Males are smaller than females
Males have a hook which is used
to attach to a female during
mating
On the hook there are spicules
that protrude from the cloaca and
are inserted into the genital pore
of the female
Fertilization is internal
Life cycle involves many hosts

21. Phylum
Arthropoda

22. Class Arachnida
In most species, the male transfers sperm to the female in a package, or
spermatophore. Complex courtship rituals have evolved in many arachnids
to ensure the safe delivery of the sperm to the female.
Arachnids usually lay yolky eggs, which hatch into immatures that resemble
adults.
Scorpions bear live young.

23. Class Merostamata
Horseshoe crabs migrate to
shallow coastal waters to
reproduce.
Males select a female and cling
onto her back.
The female digs a hole in the
sand and lays her eggs while the
male fertilizes them.
The female can lay between
60,000–120,000 eggs in batches
of a few thousand at a time.

24. Class DiplodaMale millipedes can be differentiated from female millipedes by the presence of
one or two pairs of legs modified into gonopods. These modified legs are used to
transfer sperm packets to the female.
A few species are parthenogenetic– a form of asexual reproduction found in
females, where growth and development of embryos occurs without fertilization
Females lay between ten and three hundred eggs at a time
genital openings are located on the third segment
the male has one or two penises which deposit the sperm packets onto the
gonopods. The female has a vulva, which is covered by a small hood-like cover, and
is used to store the sperm after mating

25. Class ChilopodaSexual:
Males deposit a spermatophore for
the female to take up
the male undertakes a courtship
dance to encourage the female to
engulf his sperm.
Asexual:
A few species are parthenogenetic
centipedes

26. Class Insecta
Reproduction varies widely because of
the amount of insect species
Most have separate sexes and reproduce
sexually
Most have internal fertilization because
the gametes would not survive long
otherwise
After fertilization, an embryo may
develop through metamorphosis from
larvae stages to adult stages or by direct
development

27. Class Malacostraca
The majority of crustaceans have separate
sexes and reproduce sexually.
A small number are hermaphrodites,
including barnacles. Some may even change
sex during the course of their life.
Parthenogenesis is also widespread among
crustaceans
In many groups of crustaceans, the fertilized
eggs are simply released into the water
column, while others have developed a
number of mechanisms for holding on to the
eggs until they are ready to hatch

28. Phylum
Echinodermata

29. Class Asteroidea
Class Holothuroidea
Class Ophiuroidea
Class Echinoidea
Class Crinoidea

30. Sexual Reproduction:
Separate sexes and external fertilization after releasing egg and
sperm into the water column
Asexual Reproduction:
Can regenerate arms, spines, organs and tissues. After
fragmentation, species can regenerate a whole new organism

31. Phylum
Chordata

33. Class Chondrichthyes
Reproduce Sexually
Most speices are
viviparous—give birth
to live young
Fertilization is internal

34. Class actinopterygii
Reproduce Sexually
Most species are oviparous—lay eggs
Lay large number of eggs
Fertilization is External

35. Class Sarcopterygii
Reproduce Sexually
Most species are
ovapirous and lay large
amounts of eggs
Fertilization is External

36. Class Amphibia
Have eggs that lack a shell and
will dry out if not kept moist
Fertilization is external
The male releases sperm over
the eggs as the female sheds
them
The eggs may be incubated by
either male or female in their
mouths, on their backs, or in
their stomachs

37. Class Reptilia
Have protected,
shelled egg: amniotic
eggs
In the amniotic eggs,
the embryo is
protected by the
amnion and the shell
It is kept moist by the
albumen and fed by
the yolk
Some tissues in the
egg function in waste
storage and gas
exchange
All species reproduce
sexually
Internal fertilization

39. ClassAves
Female birds have one ovary
Reproduce sexually with internal fertilization
Have amniotic eggs
Eggs are brooded by female, male or both depending on species

40. Class
Mammalia

41. Most have uterus with placenta for nourishing
the fetus
Entire development of offspring takes place
inside uterus, nourished solely by mother
A few mammals lay eggs (platypus and
echidnas)
A few develop offspring first in uterus and then
complete development in a pouch (marsupials)

42. Important Evolutionary
Advantages in Vertebrates:
Amniotic Egg: provides a complete life support
system for a developing embryo and allows for
larger eggs and can develop in dryer
environments
Femalereproductivetissues
Malereproductivetissues