Introduction to Invertebrates
Chapter 29
Mader: Biology 8th Ed.
Outline
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Evolution of Animals
Sponges
Cnidarians and Comb Jellies
– Hydra
– Obelia
Bilateral Symmetry
– Flatworms
– Roundworms
Mader: Biology 8th Ed.
Evolution of Animals
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All animals are multicellular heterotrophic
organisms that must take in preformed food.
Classification Criteria
– Level of organization
 Cellular, tissue, organ
– Body Plan
 Sac, tube-within-a-tube
– Segmentation
 Segmentation leads to specialization.
Mader: Biology 8th Ed.
Evolution of Animals
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Symmetry
 Radial - Two identical halves.
 Bilateral - Definite right and left halves.
Type of Coelom
 Pseudocoelom
 Coelom
 Protostome - First embryonic opening
becomes the mouth.
 Dueterostome - Second embryonic
opening becomes the mouth.
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Multicellularity
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Sponges
– Only level of animal to have cellular
organization.
– Saclike bodies perforated by many pores.
– Beating of flagella produces water
currents that flow through pores into
central cavity and out osculum.
– Sessile filter feeders.
– Asexual reproduction by fragmentation or
budding.
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Simple Sponge Anatomy
Mader: Biology 8th Ed.
True Tissue Layers
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Total of three possible germ layers.
– Ectoderm, endoderm, and mesoderm
Animals in phlyum Ctenophora (comb
jellies) and in phylum Cnidaria (cnidarians)
develop only ectoderm and endoderm.
– Diploblasts
 Radially symmetrical
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Cnidarian and Comb Jelly
Mader: Biology 8th Ed.
Comb Jellies
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Small, transparent, and often luminescent.
Most of body composed of mesoglea.
Largest animals propelled by beating of cilia.
Capture prey with tentacles.
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Cnidarians
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Tubular animals that most often reside in
shallow marine waters.
– Polyp and medusa body forms.
– Specialized stinging cells (cnidocytes).
 Fluid-filled capsule, nematocyst.
– Two-layered body sac.
 Outer layer - Protective epidermis.
 Inner layer - Gastrovascular cavity.
– Nerve net found throughout body.
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Cnidarian Diversity
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Hydra
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Freshwater cnidarians.
– Small tubular poly body about one-quarter
inch in length.
 Gastrovascular cavity is central cavity.
– Tentacles can respond to stimuli.
– Can reproduce sexually and asexually.
Mader: Biology 8th Ed.
Hydra
Mader: Biology 8th Ed.
Obelia
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A colony of polyps enclosed by a hard,
chitinous covering.
– Feeding polyps
 Extend beyond covering
 Have nematocyst-bearing tentacles.
– Reproductive polyps
 Budding of new polyps.
Also has sexual reproduction (medusae)
stage.
Mader: Biology 8th Ed.
Obelia
Mader: Biology 8th Ed.
Bilateral Symmetry
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Ribbon worms (phylum Nemertea)
– Have distinctive proboscis
Flatworms (phylum Platyhelminthes)
– Majority are parasitic
– Organ-level organization
 No specialized circulatory or respiratory
structures.
– Have undergone cephalization
– Ladder-type nervous system
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Free-living Flatworms
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Planarians (genus Dugesia)
– Live in freshwater habitats.
– Head is bluntly arrow shaped.
 Auricles function as sense organs.
 Two light-sensitive eye spots.
– Three kinds of muscle layers:
 Outer circular layer
 Inner longitudinal layer
 Diagonal layer
Mader: Biology 8th Ed.
Planarians
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Excretory organ functions in osmotic
regulation and water excretion.
Can reproduce asexually
Hermaphroditic
 Practice cross-fertilization
Mader: Biology 8th Ed.
Mader: Biology 8th Ed.
Parasitic Flatworms
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Parasitic flatworms are flukes (trematodes)
and tapeworms (cestodes).
– Well-developed nerves and
gastrovascular cavity are unnecessary.
Flukes
– Usually named for type of vertebrate
organ they inhabit.
 Reproductive system well developed.
 Usually hermaphroditic.
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Transmission of Schistosomiasis
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Parasitic Flatworms
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Tapeworms
– Have anterior region with modifications for
attachment to intestinal wall of host.
 Behind head region, scolex, a long
series of proglottids are found.
 Segments each containing a full set
of both male and female sex organs.
– Complicated life cycles.
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Life Cycle of Taenia
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Pseudocoelom
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Pseudocoelom is a false body cavity that is
incompletely lined by mesoderm.
– Provides a space for internal organs and
can serve as hydrostatic skeleton.
Roundworms (phylum Nematoda)
– Nonsegmented, generally colorless
worms.
– Several parasitic roundworms infect
humans.
Mader: Biology 8th Ed.
Roundworm Anatomy
Mader: Biology 8th Ed.
Parasitic Roundworms
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Ascaris
Trachinella - Trichinosis
Dirofilaria - Heartworms
Wuchereria - Elephantiasis
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Rotifers
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Rotifers (phylum Rotifera)
– Named for crown of cilia resembling a
rotating wheel.
 Serves as both as an organ of
locomotion and aids direction of food to
mouth.
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Rotifer
Mader: Biology 8th Ed.
Review
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Evolution of Animals
Sponges
Cnidarians and Comb Jellies
– Hydra
– Obelia
Bilateral Symmetry
– Flatworms
– Roundworms
Mader: Biology 8th Ed.
Mader: Biology 8th Ed.