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Animals: The Invertebrates
Chapter 23
Key Concepts:
All animals are multicelled, aerobic
heterotrophs
Animals originated about 900 million years
ago
Comparisons of body plans of existing
animals with fossil records reveal that there
were several trends in the evolutions of
certain lineages
Key Concepts:
Divergences gave rise to two major
lineages: those of the mollusks, annelids,
and arthropods and the other one to the
echinoderms and chordates
The arthropods, especially the insects,
have been the most successful animal
groups
Evolutionary Tree Diagram
Overview of the
Animal Kingdom
Animals
Multicellular
Heterotrophs
Oxygen is required
Sexual reproduction (some asexual)
Motile - in part of life cycle
Embryonic development
Mitotic cell divisions in embryo
Tissue layers
• Ectoderm, Endoderm, Mesoderm
Diversity in Body Plans
Vertebrates
Mammals
birds, reptiles,
amphibians, fishes
Invertebrates
No backbones
Body symmetry &
Cephalization (
sense in the head)
Gut
Body cavity
Segmentation
Examples of Body Symmetry
Radial
Live in water
Bilateral
Mirror image
Type of Body
Cavity in Animals
Gut, body cavities, segmentation
Type of Body
Cavity in Animals
Lined body cavity
Sponges
Success in Simplicity
No symmetry, tissues, or organs
Sponges
Success in Simplicity
A basket sponge releasing a cloud of sperm
Tissues in a Jellyfish
The sea nettle,
a jellyfish
(Chrysaora)
Stages in Cnidarian
Life Cycles
Both polyp and
medussa body
forms
Physalia
Portuguese
Man-of-War
Flatworms:
Turbellarians, Flukes & Tapeworms
Nervous system
in a Planarian
Reproductive
system in a
Planarian
Tapeworms
Parasitic
Scolex
Proglottids
Hermaphroditic
Roundworms
Most abundant multicelled animal
Bilateral symmetry
Cylindrical body
Cuticle
Complete digestive system
Male and female
Flukes
Parasitic
Sexual or asexual
phases
Two hosts
Snail
Human
Life Cycle of
Schistosoma japonicum
A Sampling of Mollusks
Mollusk
Soft body
Shell
Mantle
Fleshy foot
Gastropods-snails
Chitons
Bivalves-clams
Cephalopods-squid
Evolutionary Experiments
with Body Plans
Radula is used to
scrape food into
the mouth
Evolutionary Experiments
with Body Plans
Body Plan of
a clam
Evolutionary Experiments
with Body Plans
Body Plan of a
cuttlefish,
a cephalopod
Annelids: Segments Galore
Bilateral
Segmented
Earthworms
Leeches
Polychaetes
Earthworm Body Plan
Coelomic chambers
A nephridium
Earthworm Body Plan
Portion of the closed
circulatory system
Part of the
digestive system
Earthworm Body Plan
Part of the
nervous system
Arthropods: The Most
Successful Organisms on
Earth-Arthropods
Over one million species
Trilobites (extinct)
Chelicerates
Spiders
Crustaceans
Barnacles and crabs
Uniramians
Centipedes, millipedes, insects
Adaptations of Insects and
Other Arthropods
Hardened exoskeleton
Jointed appendages
Fused and modified segments
Respiratory structures
Specialized Sensory Structures
Division of labor
A Look at Spiders
Organization of
a Spider Body
A Look at Crustaceans
Shrimps, lobsters, crabs, barnacles
A Copepod
A Lobster
Life Cycle of a Crab
Continuous molting
A Look at Insect Diversity
Head, thorax, abdomen
Sensory antennae
Mouthparts
3 pairs of legs
2 pairs of wings
Malphigian tubules
Waste disposal
Life cycles
A Look at Insect Diversity
Examples of Appendages
Grasshopper
Fly
Butterfly
Mosquito
Examples of Post-Embryonic
Development
Silverfish
True bugs
Fruit flies
The Puzzling Echinoderms
Echinoderms
Sea star
 Body walls
Spines, spicules
Sea urchin
 Radial symmetry
Sea cucumber
 Decentralized nervous
system
Brittle stars
 Water-vascular system
The Puzzling Echinoderms
Sea urchin
Key Aspects of the Radial
Body Plan of a Sea Star
In Conclusion
Animals are multicellular, aerobic
heterotrophs that ingest or parasitize
other organisms
Animals range from structurally
simple placozoans and sponges to
vertebrates
In Conclusion
Almost all animals more complex
than cnidarians show bilateral
symmetry, form tissues, organs, and
organ systems
All mollusks have a fleshy soft body,
and a mantle
In Conclusion
 The annelids, have a segmented body,
complex organs, and coelomic chambers
 Arthropods are the most successful of all
groups in terms of diversity, numbers,
distribution, defenses, and capacity to
exploit food resources
 Echinoderms have spines, spicules, or
plates in their body wall

developed by M. Roig