Comparing Invertebrates
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The First Multicellular Animals
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• Fossils evidence from Ediacara Hills, Australia
show some of the earliest and most primitive
animals (575-543 mya). Altough these animals
were bilateral and segmented, they were probably
simple and with little internal specialization.
Beginnings of Invertebrate Diversity
(The Cambrian Explosion)
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Burgess Shale fossil evidence shows that animals became
more diverse after the Cambrian period (544 mya). Some
animals had evolved shells, skeletons, and other hard body
parts - which were preserved as fossils.
The Cambrian Explosion Video Clip: http://www.pbs.org/wgbh/evolution/library/03/4/l_034_02.html
Invertebrate Phylogeny
Invertebrate Cladogram
Echinoderms Chordates
Arthropods
Annelids
Mollusks
Radial
Symmetry
Roundworms
Flatworms
Cnidarians
Radial
Symmetry
Sponges
Pseudocoelom
Coelom
Protostome Development
Three Germ Layers;
Bilateral Symmetry
Tissues
Multicellularity
Single-celled
ancestor
Deuterostome
Development
Cladogram
(shows evolutionary relationships)
Evolutionary Trends
• Specialized Cells, Tissues, & Organs
simple --> complex
• Body Symmetry
asymmetrical --> radial --> bilateral
• Cephalization
no head --> head
• Segmentation
no body segments --> specialized body segments
• Coelom Formation (body cavity)
acoelomate --> pseudocoelomate --> true coelom
• Embryological Development
protostome --> deuterostome
Comparing Invertebrates
Major
Characteristics Sponges
Cnidarians
Flatworms
Roundworms
Germ Layers
Absent
Two
Three
Three
Body
Symmetry
Absent
Radial
Bilateral
Bilateral
Cephalization
Absent
Absent
Present
Present
Section 29-1
Coelom
Absent
Absent
Absent
Pseudocoelom
Early
Development
—
—
Protostome
Protostome
Major
Characteristics Annelids
Mollusks
Arthropods
Echinoderms
Germ Layers
Three
Three
Three
Three
Body
Symmetry
Bilateral
Bilateral
Bilateral
Radial (adults)
Cephalization
Present
Present
Present
Absent (adults)
Coelom
True coelom
True coelom
True coelom
True coelom
Early
Development
Protostome
Protostome
Protostome
Deuterostome
Comparing Invertebrates
Chart
Invertebrate Digestive Systems
simplest animals: intracellullar digestion (inside cells)
complex animals: extracellular digestion (digestive tract)
Intestine
Gizzard
Crop
Pharynx
Mouth
Mouth/anus
Gastrovascular
cavity
Anus
Gastrovascular
cavity
Annelid
Cnidarian
Pharynx Crop
Anus
Pharynx
Mouth
Mouth/anus
Flatworm
Stomach
and
digestive
glands
Rectum
Intestine
Arthropod
Invertebrate Respiratory Systems
Aquatic invertebrates: diffusion and/or gills
Terrestrial invertebrates: book lungs, tracheal tubes, etc.
Tracheal
tubes
Gill
Siphons
Movement of water
Spiracles
Insect
Mollusk
Airflow
Spider
Book
lung
Invertebrate Circulatory Systems
simplest animals: diffusion through body surface
complex animals: heart(s) to pump blood in a circulatory system
Heartlike
structure
Small vessels in
tissues
Hearts
Blood
vessels
Heart
Sinuses
and organs
Insect
Open Circulatory System
Blood is partially contained.
Blood is pumped into sinuses.
Blood comes in direct contact with tissues
Blood
Heartlike vessels
structures
Annelid
Closed Circulatory System
Blood is contained in vessels.
More efficient (active animals)
Invertebrate Excretory Systems
Aquatic invertebrates: diffusion through body tissues.
Terrestrial invertebrates: nephridia, malpighian tubules, etc.
Excretory Flame cells
tubules
Flatworm
Nephrostome
Excretory pore
Flame cell
Excretory
tubule
Nephridia
Digestive tract
Annelid
Malpighian tubules
Arthropod
Invertebrate Nervous Systems (Response)
Centralization: nerve cells are more concentrated.
Cephalization: ganglia are organized into a brain (controls body)
Specialization: special sense organs to detect light, sound, movement, etc.
Arthropod
Brain
Ganglia
Ganglia
Brain
Nerve
Cells
Flatworm
Mollusk
Cnidarian
Movement and Support
Hydrostatic skeleton: fluid filled body cavity that supports muscles.
Exoskeleton: hard outer skeleton made of chitin
Endoskeleton: internal structural support
Type of
Skeleton
Sponges
Cnidarians
Hydrostatic
X
Flatworms
X
Roundworms
X
Exoskeleton
Endoskeleton
Type of
Skeleton
Hydrostatic
Exoskeleton
Endoskeleton
Simple
(spicules or
spongin)
Annelids
X
Mollusks
Arthropods
Echinoderms
Some
Some
(shells)
X
X
Reproduction
Asexual: reproduce rapidly in favorable conditions (genetically identical)
Sexual: creates genetic diversity with a combination of sperm and egg
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Porifera
Arthropoda
Reproduce asexually (budding)
or sexually by releasing sperm
which fertilizes and egg.
(external fertilization)
Reproduce sexually when male
deposits sperm inside the female
to fertilize eggs.
(internal fertilization)