Animals I –
The Invertebrates
Chapter 23
Biology Concepts and Applications, Eight Edition, by Starr, Evers, Starr. Brooks/Cole,
Cengage Learning 2011.
23.1 Old Genes, New Drugs
 Vertebrates  Animal with backbone
• Mammals, birds, reptiles, amphibians, and fish
 Invertebrates  no backbone
• Majority of animals (97%)
Old Genes, New Drugs
 Cone Snails
• Lead to the development of new drugs
• Produce venom that subdues their prey
• Peptide in venom  interferes with ability to
feel pain
• Prevents prey from damaging the snail
• Ziconotide  injectable pain killing drug is a
synthetic version of the peptide
• No additive unlike morphine
Old Genes, New Drugs
 Cone Snails
• Other drugs control convulsions and seizures
• Venom gene found in fruit flies and humans
• In humans, the gene helps repair blood
vessels
 Mutations  change biochemistry, body plans,
or behavior
• Source of unique traits that define each
lineage
23.2 Animal Traits and Trends
 Animals are
• multicelled heterotrophs with unwalled cells
• Most ingest food and that move about for at least
part of their life cycle
 Evolution
•
•
•
•
Protist ancestor  Multicellular
No tissues Vs. Tissues
Radial Symmetry Vs. Bilateral Symmetry
Protostome Development Vs. Deuterostome
Development
Animal Traits and Trends
 Animals develop in a series of stages
• Ectoderm, endoderm, and often mesoderm form
in the early embryo
• Cells interact in functional units (epithelium and
connective tissues)
Tissues
 Tissues develop from embryonic germ layers
 Ectoderm
• Outermost tissue layer of an animal embryo
 Endoderm
• Innermost tissue layer of an animal embryo
 Mesoderm
• Middle tissue layer of a three layered animal
embryo
• Most animal groups have organs derived from
this layer
Animal Groups
Comparing Key Groups
 Evolutionary trends toward
• Greater size
• Compartmentalization (division of labor among
cells, tissues, and organs)
• Integration of specialized activities that keep the
organism alive
Body Symmetry: Radial and Bilateral
 Radial Symmetry
• Having parts arranged around a central axis, like
spokes around a wheel
 Bilateral Symmetry
• Having paired structures so the right and left
halves are mirror images
 Most animals are bilateral
Fig. 23.2, p.361
Bilateral Animals: Two Major Branches
 Protostomes
• First opening on the embryo becomes the mouth
 Deuterostomes
• First opening on the embryo becomes the anus
• Second opening on the embryo becomes the
mouth
Body Cavities
 Most bilateral animals have a coelom and a
complete gut
• Coelom  body cavity lined with tissue derived
from mesoderm
 Pseudocoelom  unlined body cavity
• Roundworms enclose their gut in an unlined cavity
Fig. 23.3, p.363
Fig. 23.3, p.363
Fig. 23.3, p.363
Body Organization
 Cephalization
• Nerve and sensory cells concentrated at the head
 Segmentation
• Repetition of body units, front-to-back
23.3 Animal Origins and Early Radiations
 Colonial theory of animal origins
• Animals arose from a colony of flagellated protist
cells, similar to modern choanoflagellates
• Choanoflagellates  member of the protist
group most closely related to animals
 Placozoans
• Simplest known modern animals
• Gene sequencing data show placozoans are
similar to choanoflagellates
• Asymmetrical flat body, four types of cells, and a
small genome
Choanoflagellates and Placozoans
Placozoans
Choanoflagellates
Ancestors of Modern Animals
 Ediacarans
• Oldest animal fossils
• Date back about 600 million years
 Cambrian explosion
• A great adaptive radiation during the Cambrian
gave rise to most modern lineages
• Rising oxygen levels and changes in global climate
may have played a role
• Supercontinents were breaking up
• Isolated populations  increasing allopatric
speciation
Animal Family Tree
placozoans
sponges cnidarians flatworms rotifers mollusks annelids roundworms arthropods echinoderms chordates
protostomes,
mouth forms first in embryos
radial ancestry,
two germ layers
no true tissues
deuterostomes,
anus forms first in embryos
bilateral ancestry,
three germ layers
true tissues
multicelled body
fungi
choanoflagellates
Fig. 23.6, p.364
Key Concepts:
INTRODUCING THE ANIMALS
 Animals
• Multicelled heterotrophs (ingest other organisms)
• Grow and develop through a series of stages
• Actively move about during all or part of life cycle
 Cells of most animals form tissues and
extracellular matrixes
Key Concepts:
INTRODUCING THE ANIMALS (cont.)
 Earliest animals were small and structurally
simple
 Their descendants evolved larger bodies with a
more complex structure and greater integration
among specialized parts
Key Concepts:
INTRODUCING THE ANIMALS (cont.)
 Animals’ body plans vary
• Bodies may or may not show symmetry
• There may or may not be an internal body cavity,
a head, or division into segments.
 An early divergence gave rise to two major
branches: protostomes and deuterostomes
23.4 Sponges (Phylum Porifera)
 Sponges
• Aquatic invertebrates
• No symmetry, no tissues, or no organs
• Flattened cells line the body wall (many pores;
spikes of silica and/or proteins)
• Filter feeders (flagellated collar cells absorb food;
amoeboid cells digest and distribute it)
• Hermaphrodites  make both eggs and sperm
• Zygote develops into free-living larva
• Larva  preadult stage
Sponges
Sponge Body Plan
23.5 Cnidarians (Phylum Cnidaria)




Cnidarian radially symmetrical invertebrates
Two tissue layers
Uses tentacles with stinging cells to capture food
Nematocyts
• Stinging organelle
23.5 Cnidarians (Phylum Cnidaria)
 Jellyfishes, corals, and sea anemones
• Radial symmetry, tentacled carnivores
• Gastrovascular cavity (respiration and digestion)
• True epithelial tissues with a jellylike matrix in
between
• Simple nervous system (nerve net)
• Nerve net  mesh of nerve cells that allows
movement and other behavior
• Hydrostatic skeleton
• of soft-bodies invertebrates, a fluid filled chamber
that muscles act on, redistributing the fluid
Cnidarian Body Plans
outer epithelium
(epidermis)
gastrovascular
cavity
mesoglea
(matrix)
inner epithelium
(gastrodermis)
gastrovascular
cavity
Fig. 23.9, p.366
Unique Cnidarian Weapons
 Nematocysts  Used to capture prey and for
defense. Responses to touch!!
lid
capsule's
trigger
(modified
cilium)
barbs on
discharged
thread
exposed
barbed
thread in
capsule
nematocyst (capsule at free surface of epidermal cell)
Fig. 23.10, p.366
mesogleafilled bell
tentacles with
nematocysts
Fig. 23.10, p.366
Cnidarian Life Cycles
Key Concepts: STRUCTURALLY
SIMPLE INVERTEBRATES
 Sponges and placozoans have no body
symmetry or true tissues
 Cnidarians are radially symmetrical, with two
tissue layers and a gelatinous matrix between
the two
23.6 Flatworms (Phylum Platyhelminthes)
 Flatworm
• Bilaterally symmetrical invertebrate with organs
but no body cavity
 Free-living turbellarians (planarians), parasitic
tapeworms and flukes
•
•
•
•
Simplest animals with organ systems
Bilateral protostomes
Paired nerve cords, ganglia
Hermaphrodites
Planarian Organ Systems
Fig. 23.13, p.368
Fig. 23.13, p.368
Parasite Life Cycle: Tapeworm
proglottids
Larvae, each
with inverted
scolex of future
tapeworm,
become
encysted in
intermediate
host tissues
(e.g., skeletal
muscle).
A human, the
definitive host, eats
infected, undercooked
beef, which is mainly
skeletal muscle.
scolex
scolex
attached
to wall of
intestine
one
proglottid
Inside each fertilized egg, an embryonic,
larval form develops. Cattle may ingest
embryonated eggs or ripe proglottids,
and so become intermediate hosts.
Each sexually mature
proglottid has female
and male organs. Ripe
proglottids containing
fertilized eggs leave the
host in feces, which
may contaminate water
and vegetation.
Fig. 23.15, p.369
23.7 Annelids
 Bilateral segmented worm with a coelom,
complete digestive system
 Segmented worms (earthworms, polychaetes)
and leeches
• Closed circulatory system
• Digestive and excretory systems, soluteregulating nephridia
• Nervous system, ganglia in each segment
• Muscles and fluid in chambers act as a
hydrostatic skeleton
• Hermaphrodites
Polychaetes
Fig. 23.16, p.370
Oligochaetes - Earthworm Body Plan
Fig. 23.18, p.371
head
end
secretory organ
Fig. 23.18, p.371
longitudinal muscle
dorsal blood vessel
circular muscles
fluid-filled
coelomic
chamber
nephridium
gut cavity
bristle
(retracted)
cuticle
ventral blood vessel
nerve cord
Fig. 23.18, p.371
2-5 hearts
Fig. 23.18, p.371
Fig. 23.18, p.371
Fig. 23.18, p.371
Fig. 23.18, p.371
Earthworm Motion
23.8 Mollusks (Phylum Mollusca)
 Invertebrate with a reduced coelom and a
mantle
• Mantle  skirtlike extension of the upper body
wall that covers a mantle cavity
 Bilaterally symmetrical
 Dwell in seas, fresh water, or land
 One or more respiratory organs  gills
• Inside fluid-filled mantle cavity
 Digestive system is complete
Aquatic Snail Body Plan
Mollusks (Phylum Mollusca)
 Including gastropods (snails), bivalves (scallops),
chitons, nudibranchs, cephalopods
• 100,000 named species
 Gastropods
• Lower body is a broad foot
• Open circulatory system  blood leaves vesseles
and seeps through tissues before returning to the
heart
Mollusks (Phylum Mollusca)
 Bivalves
• Hinged two-part shell
• Mussels, oysters, clams, ad scallops
• Contraction of muscles pulls the two valves shut,
enclosing the body and protecting it from
predation
Cephalopods
 Closed circulatory system
• All materials are exchanged across the walls of
blood vessels (continuous network of vessels)
 The fastest (squids), largest (giant squids), and
smartest (octopuses) invertebrates
• Of invertebrates  Octopuses have the largest
brain relative to body size, and show the most
complex behavior
 Have a mantle
• Sheetlike part of the body mass, draped back on
itself
Cephalopods
23.9 Roundworms (Phylum Nematoda)
 Unsegmented worm with a pseudocoelom and a
cuticle that is molted as the animal grows
 More than 22,000 kinds of roundworms
•
•
•
•
Free-living decomposers or parasites
Some agricultural pests and human parasites
Cylindrical body with bilateral features
A cuticle that is molted  periodic shedding of an
outer body layer or part
• A complete gut
• Organ systems in a false coelom
Roundworm Body Plan
Parasitic Roundworms
Cause  stomach pain, vomiting, and appendicitis
Key Concepts:
BILATERAL INVERTEBRATES
 Most animals show bilateral symmetry
 Bilateral animals have tissues, organs, and
organ systems
 All adult tissues arise from two or three simple
layers that form in early embryos
23.10 Arthropods (Phylum Arthropoda)
 Invertebrate with jointed legs and a hard
exoskeleton that is periodically molted
 More than 1 million arthropod species
•
•
•
•
•
•
Trilobites (extinct)
Chelicerates
Crustaceans
Centipedes
Millipedes
Insects
Arthropod Characteristics
 Key arthropod adaptations
• Hardened exoskeleton
• Hard external parts that muscles attach to and move
• Jointed appendages
• Specialized and fused segments (wings)
• Efficient respiratory structures (aquatic -gills, land –air
conducting tubes)
• Sensory structures (eyes, antennae – touch and
odors)
• Specialized stages of development for different
environmental conditions (metamorphosis)
• Remodeling of body form during transition larva  adult
23.11 Chelicerates
 Arthropod subgroup with specialized feeding
structures (chelicerae) and no antennae
 Horseshoe crabs and arachnids (spiders,
scorpions, ticks, and mites)
chelicerae
Fig. 23.25, p.376
23.12 Crustaceans
 Mostly marine crustaceans (crabs, lobsters,
barnacles, krill, and copepods)
 Two pairs of antennae
Lobster Body Plan
Crab Life Cycle
Molt repeatedly until they reach adult size
23.12 Insect Traits and Diversity
 Most successful of all animal groups
• Include the only winged invertebrates
 Six legs
 Two antennae
 Some have wings
Insect Development
Fig. 23.31, p.378
Fig. 23.31, p.378
Key Concepts:
THE MOST SUCCESSFUL ANIMALS
 In diversity, numbers, and distribution,
arthropods are the most successful animals
 In the seas, crustaceans are the dominant
arthropod lineage; on land, insects rule
23.14 The Importance of Insects
THE GOOD!!
 Pollinators
• Contribute to an increased rate of speciation in
both pollinator lineages and flowering plants
• Pesticides and diseases  reduce numbers of
pollinators
 Food Source for birds, amphibians, and reptiles
 Keep wastes and remains from piling up and
help distribute nutrients through the ecosystem
The Importance of Insects
THE BAD!!
 Competitors for Crops
• Devore 1/4th to 1/3rd of all crops grown in the US
• Damage plant and fruits yields (50%)
 Vectors for Disease
• Spread human pathogens
• Example: malaria, viruses, bubonic plague
23.14 Echinoderms
 Invertebrates with a water-vascular system and
hardened plates and spines embedded in the
skin or body
 Water-vascular system
• A system of fluid-filled tubes and tube feet that
function in locomotion
Echinoderms
 Sea stars, sea urchins, sea cucumbers, etc.
• Invertebrates of the deuterostome lineage
• Exoskeleton with spines, spicules, or plates of
calcium carbonate
• Water-vascular system with tube feet
• Adults are radial, but bilateral traits appear in
larval stages and other features
Echinoderms: “Spiny-Skinned”
Fig. 23.34, p.381
Fig. 23.34, p.381
Fig. 23.34, p.381
Fig. 23.34, p.381
canal of
water–
vascular
system
in a sea
star
a tube foot’s water-filled bulb
Fig. 23.34, p.381
Key Concepts:
ON THE ROAD TO CHORDATES
 Echinoderms are on the same branch of the
animal family tree as the chordates
 They are invertebrates with bilateral ancestors,
but adults now have a decidedly radial body plan
Comparative Summary of Body Plans
Animation: Body plan of a sea star
Animation: Body plan of a sponge
Animation: Chelicerates
Animation: Cnidarian body plans
Animation: Cnidarian life cycle
Animation: Crab life cycle
Animation: Crustaceans
Animation: Earthworm body plan
Animation: Insect development
Animation: Molluscan classes
Animation: Nematocyst action
Animation: Planarian organ systems
Animation: Roundworm body plan
Animation: Snail body plan
Animation: Tapeworm life cycle
Animation: Types of body cavities
Animation: Types of body symmetry