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Chapter 29
Introduction to
Invertebrates
Outline
Evolution of Animals
Multicellularity
Sponges
True Tissues
Cnidarians and Comb Jellies
- Hydra
- Obelia
Bilateral Symmetry
Flatworms
Roundworms
Body Cavities
Acoelomates
Psuedocoelomates
Eucoelomates
Introduction to
Invertebrates
2
Evolution of Animals
Introduction to
Invertebrates
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
3
Evolution of Animals
Introduction to
Invertebrates
4
Classification Criteria, cont
Symmetry
- Radial - Two identical halves
- Bilateral - Definite right and left halves
Type of Coelom
- Pseudocoelom
- Coelom
Early Developmental Pattern
- Protostome - First embryonic opening becomes the
mouth
- Dueterostome - Second embryonic opening
becomes the mouth
Animals:
Multicellular, Heterotrophic Eukaryotes
5
Traditional Phylogenetic Tree of Animals
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Multicellularity
Sponges
Introduction to
Invertebrates
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
7
Simple Sponge Anatomy
8
True Tissue Layers
Introduction to
Invertebrates
Total of three possible germ layers
Ectoderm
Endoderm, and
Mesoderm
phlya Ctenophora and Cnidaria develop only
ectoderm and endoderm
Diploblasts
Radially symmetrical
9
Comb Jellies
Introduction to
Invertebrates
Small, transparent, and often luminescent
Most of body composed of mesoglea
Largest animals propelled by beating of cilia
Capture prey with tentacles
10
Comb Jelly Compared to Cnidarian
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Cnidarians
Introduction to
Invertebrates
12
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
13
Hydra
Introduction to
Invertebrates
14
Freshwater cnidarian
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
Anatomy of Hydra
15
Obelia
Introduction to
Invertebrates
16
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
Obelia Life Cycle
17
Bilateral Symmetry
Introduction to
Invertebrates
18
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
Ribbon Worm, Lineus
19
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 layer
- Inner longitudinal layer
- Diagonal layer
Introduction to
Invertebrates
20
Planarian Anatomy
21
Planarians
Introduction to
Invertebrates
Planarians, cont.
Excretory organ functions in osmotic regulation
and water excretion
Can reproduce asexually
Hermaphroditic
- Practice cross-fertilization
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Parasitic Flatworms
Introduction to
Invertebrates
23
Parasitic flatworms are flukes (trematodes) and
tapeworms (cestodes)
Well-developed nerves and gastrovascular cavity
are unnecessary
Flukes
Reproductive system well developed
Usually hermaphroditic
Life Cycle of Schistosomiasis
24
Parasitic Flatworms
Introduction to
Invertebrates
25
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 a Tapeworm, Taenia
26
Pseudocoelom
Introduction to
Invertebrates
27
Pseudocoelom:
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)
Non-segmented, generally colorless worms
Several parasitic roundworms infect humans
Roundworm Anatomy
28
Parasitic Roundworms
Ascaris – Intestinal roundworm
Trachinella - Trichinosis
Dirofilaria - Heartworms
Wuchereria - Elephantiasis
Introduction to
Invertebrates
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Filarial Worm
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Rotifers
Introduction to
Invertebrates
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
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Review
Evolution of Animals
Multicellularity
Sponges
True Tissues
Cnidarians and Comb Jellies
- Hydra
- Obelia
Bilateral Symmetry
Flatworms
Roundworms
Body Cavities
Acoelomates
Psuedocoelomates
Eucoelomates
Introduction to
Invertebrates
33
Ending Slide Chapter 29
Introduction to
Invertebrates