Mader: Biology 8 th Ed. Introduction to Invertebrates Chapter 29.

Mader: Biology 8th Ed.

Introduction to Invertebrates

Chapter 29


Outline

• Evolution of Animals• Sponges• Cnidarians and Comb Jellies

– Hydra– Obelia

• Bilateral Symmetry– Flatworms– Roundworms


Evolution of Animals

• 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.


Evolution of Animals

– SymmetryRadial - Two identical halves.Bilateral - Definite right and left halves.

– Type of CoelomPseudocoelomCoelom

Protostome - First embryonic opening becomes the mouth.

Dueterostome - Second embryonic opening becomes the mouth.


Multicellularity

• 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.


Simple Sponge Anatomy


True Tissue Layers

• 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


Cnidarian and Comb Jelly


Comb Jellies

• Small, transparent, and often luminescent.• Most of body composed of mesoglea.• Largest animals propelled by beating of cilia.• Capture prey with tentacles.


Cnidarians

• 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.


Cnidarian Diversity


Hydra

• 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.


Hydra


Obelia

• A colony of polyps enclosed by a hard, chitinous covering.– Feeding polyps

Extend beyond coveringHave nematocyst-bearing tentacles.

– Reproductive polypsBudding of new polyps.

• Also has sexual reproduction (medusae) stage.


Obelia


Bilateral Symmetry

• 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


Free-living Flatworms

• 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 layerInner longitudinal layerDiagonal layer


Planarians

– Excretory organ functions in osmotic regulation and water excretion.

– Can reproduce asexually– Hermaphroditic

Practice cross-fertilization


Parasitic Flatworms

• 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.


Transmission of Schistosomiasis


Parasitic Flatworms

• 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.


Life Cycle of Taenia


Pseudocoelom

• 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.


Roundworm Anatomy


Parasitic Roundworms

• Ascaris• Trachinella - Trichinosis• Dirofilaria - Heartworms• Wuchereria - Elephantiasis


Rotifers

• 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.


Rotifer


Review

• Evolution of Animals• Sponges• Cnidarians and Comb Jellies

– Hydra– Obelia

• Bilateral Symmetry– Flatworms– Roundworms

Mader: Biology 8 th Ed. Introduction to Invertebrates Chapter 29.

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Transcript of Mader: Biology 8 th Ed. Introduction to Invertebrates Chapter 29.