2. 23.1 What Is an Animal?

3. What Is an Animal?
Only animals pass through a blastula stage in embryonic development.
Blastula: a hollow, fluid-filled ball of cells that forms once an egg is fertilized by sperm

4. What Is an Animal? All animals are: Multicelled
Heterotrophs (they cannot make their own food)
Composed of cells that do not have cell walls

5. 23.2 Lessons from the Animal Family Tree

6. Animal Family Tree Figure 23.2 Porifera Cnidaria Platyhelminthes
Annelida
Mollusca
Nematoda
Arthropoda
Echinodermata
Chordata
(sponges)
(flatworms)
(roundworms)
bilateral symmetry
tissues
symmetry
ancestral protist
Figure 23.2

7. Animal Family Tree
Except for the sponges in Porifera, the members of all the phyla have bodies composed of tissues.
Except for Porifera and Cnidaria, all phyla reviewed exhibit bilateral symmetry.
Cnidaria exhibits radial symmetry
Porifera exhibits no symmetry

8. Symmetry (a) Radial symmetry: Symmetry around a central point
(b) Asymmetry:
No planes of
symmetry
(c) Bilateral symmetry:
Symmetry across the
sagittal plane
sagittal
plane
Figure 23.3

9. Animal Family Tree The members of all phyla reviewed other than
Porifera
Cnidaria
Platyhelminthes
Posess a central body cavity known as a coelom.

10. of uninterrupted tissue.
tissue from
exterior to gut
gut (digestive
tract)
flatworm
No coelom. Phylum Platyhelminthes, composed of flatworms, is one of the phyla
that has no coelom. Note that from its gut to its exterior, the flatworm is composed
of uninterrupted tissue.
coelom
gut (digestive
tract)
earthworm
Coelom. The earthworm is one of many animals that has a coelom — a fluid-filled
central cavity that usually surrounds the gut.
Figure 23.4

11. 23.3 Across the Animal Kingdom: Nine Phyla

12. Sponges
Phylum Porifera’s sponges live by drawing water into themselves through a series of tiny pores on their exterior and then filtering the food from this water while extracting oxygen from it.

13. Sponges Asculum Inner cells with flagella create currents.
The currents
cause water to
flow into pores
and out the
osculum at top.
Figure 23.5

14. Jellyfish
Phylum Cnidaria (jellyfish, sea anemones, hydras, and reef-building coral animals) use stinging tentacles to capture prey
Many cnidarians have two stages of life
Adult, medusa stage of life: swims in the water
Immature polyp stage of life: remains fixed to a solid surface.

15. Cnidarians medusa mesoglea gastrovascular cavity tentacles mouth mouth
polyp
Figure 23.6

16. Flatworms
Phylum Platyhelminthes (flatworms) contains mostly small creatures, dwelling either in aquatic or moist terrestrial environments.
Flatworms have bilateral symmetry and organs, but have no coelom or system of blood circulation.

17. Flatworm
Figure 23.7

18. Worms
The worms of phylum Annelida provide a clear example of body sementation.
Most annelids are marine, and some are freshwater.
Common earthworms are terrestrial.

19. Annelid Diversity
Figure 23.9

20. Molluscs Three important classes of phylum Mollusca
Gastropods (snails, slugs)
Bivalves (oysters, clams, mussels)
Cephalopods (octopus, squid, nautilus)
All molluscs posess a fold of skin-like tissue called a mantle that usually secretes material that forms a shell.

21. Body Plan of a Mollusc heart mantle gill shell anus stomach
tooth covered
radula
mantle
cavity
mouth
foot
mouth
Figure 23.10

22. Roundworms
The mostly microscopic roundworms of phylum Nematoda exist in enormous numbers in all kinds of habitats on Earth
A number of roundworms are agricultural pests and some are human parasites

23. Roundworms
Figure 23.11

24. Arthropods Contains three subphyla:
Uniramia (millipedes, centipedes, insects)
Chelicerata (spiders, ticks, mites, horseshoe crabs)
Crustacea (shrimp, lobsters, crabs, barnacles)
All arthropods have the following characteristics:
An exoskeleton
Paired, jointed appendages
All molt

25. Arthropod Features head thorax abdomen exoskeleton muscles joint
segments
Figure 23.12

26. Echinoderms
All members of phylum Echinodermata (sea stars, sea urchins, sea cucumbers) are marine.
All inhabit the ocean floor.

27. Sea Star Echinoderms
Figure 23.13

28. Chordates Contains three subphyla:
Vertebrata (includes all vertebrates)
Cephalochordata (lancelets)
Urochordata (includes tunicates and sea squirts)
Only the vertebrates have a vertebral column
All posess the following at some point in their lives:
Notochord
Nerve cord on the dorsal side
Post-anal tail
Series of pharyngeal slits

29. Four Universal Chordate Features
notochord
dorsal nerve cord
post-anal tail
pharyngeal slits
anus
Figure 23.15

30. 23.4 Animal Reproduction

31. Sexual Reproduction
Entails the fusion of eggs and sperm from two individuals (asexual reproduction does not)
Members of the less complex animal phyla commonly reproduce both sexually and asexually.
Sexual reproduction is the norm with more complex animals, although asexual reproduction is sometimes seen.

32. Asexual Reproduction Forms of asexual reproduction include: Budding
Fission
Parthogenesis

33. Sexual and Asexual Reproducer
reproductive
polyp
female medusa
medusa
buds
male medusa
feeding
polyps
egg
sperm
zygote
larva
blastula
polyp from budding
polyp
Figure 23.17

34. Hermaphrodites Sexual Reproduction can be practiced by hermaphrodites.
Some animals change sex over the course of their lifetimes.

35. 23.5 Egg Fertilization and Protection

36. Egg Fertilization and Protection
In animals, eggs and sperm are brought together and eggs are protected following fertilization in a number of ways.
Primitive ancestral method: parents broadcast both eggs and sperm into an aquatic environment and provide no subsequent care for the eggs that become fertilized.

37. Egg Fertilization and Protection
With movement up the scale of animal complexity, species tend to produce fewer eggs, to exhibit more directed means of bringing these eggs together with sperm, and to provide greater protection to the fertilized eggs that result.

38. Egg Fertilization and Protection
female
male
egg
mature
frog
fertilized
egg
sperm
immature
frog
developing embryo
tadpole
Figure 23.21

39. Fertilization Can be external or internal
Only some species that employ internal fertilization also employ copulation.
Other species rely on females to insert spermatophores into their own reproductive tracts.

40. Protection
Vertebrate evolution resulted in a range of strategies for protecting fertilized eggs and the offspring that develop from them.
Reptile evolution resulted in the amniotic shell, whose shell and system of membranes allows it to be laid in dry environments
Mammalian evolution produced the placental system, in which fertilized eggs develop inside a mother’s body.

41. 23.6 Organs and Circulation

42. Organs and Circulation
Organs are complex bodily structures composed of several types of tissues.
They are found in all of the animal phyla except Porifera and Cnidaria

43. Organs and Circulation
Vertebrates have closed circulation systems.
Arthropods and small molluscs have open circulation systems.

44. 23.7 Skeletons and Molting

45. Skeletons and Molting Three kinds of skeletons are found in animals
Endoskeletons
Exoskeletons
Hydrostatic skeletons
To continue their growth, animals with exoskeletons must periodically molt.

46. Table 23.1 Animal Phyla Table 23.1 Phylum Members include Live in
Characteristics
Porifera
Sponges
Ocean water (marine),
with a few living in
freshwater
Sessile (fixed in one spot) as
adults, no symmetry. System of
pores through which water flows
serves to capture nutrients. Bodies
do not have organs or true tissues.
Sexual and asexual reproduction
Cnidaria
Jellyfish, hydrozoans,
sea anemones, coral
animals
Almost all marine; a
few in freshwater
Radial symmetry, medusa (swimming)
and polyp (largely sessile) stages of
life. Use stinging tentacles to capture
prey. Have tissues. Can reproduce
sexually or by budding.
Platyhelminthes
Flatworms (including
flukes, tapeworms)
Marine, freshwater, or
moist terrestrial
environments
Bilateral symmetry, hermaphroditic,
possess organs, no central cavity.
Many are parasites. Can reproduce
through fission.
Annelida
Segmented worms
Most are marine,
some freshwater and
moist terrestrial
Distinct body segmentation in
varieties such as earthworms.
Leeches are annelids.
Mollusca
Gastropods (snails,
slugs), bivalves (oysters,
clams, mussels),
cephalopods (octopus,
squid, nautilus)
Marine, freshwater,
moist terrestrial
Mantle that can secrete material
that becomes shell; mantle cavity
housing gill or lungs.
Nematoda
Roundworms
Almost all
environments
Small size in most, but some are
several meters long. Many are crop
pests, other animal parasites.
Arthropoda
Vast group that includes
insects, spiders, mites,
crabs, shrimp, and
centipedes
Many aquatic and
terrestrial
environments
External skeleton; paired, jointed
appendages; molting; open
circulation system.
Echinodermata
Sea stars, sea urchins,
sea cucumbers
Always marine, most
on ocean floor
Generally have radial symmetry as
adults; tube feet in some species,
slow ocean floor movement in most.
Chordata
Vertebrates, lancelets,
sea squirts
Great variety of aquat-
ic and terrestrial envi-
ronments
At some point, all possess noto-
chord, dorsal nerve chord, pharyn-
geal slits, post-anal tail. Vertebrates
have vertebral column.
Table 23.1