Animals:%20The%20Invertebrates

1
Animals The Invertebrates

• Chapter 25

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Characteristics of Animals

• Multicelled heterotrophic eukaryotes
• Require oxygen for aerobic respiration
• Reproduce sexually, and perhaps asexually
• Motile at some stage
• Develop from embryos

3
Major Animal Phyla
Chordates
Echinoderms
Arthropods
Annelids
Coelomate Ancestry
Mollusks
Rotifers
Roundworms
Bilateral Ancestry
Flatworms
Radial Ancestry
Cnidarians
Sponges
Multicelled Ancestry
Figure 25.2Page 415
Single-celled, protistanlike ancestors
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Symmetry
Bilateral
Radial
Figure 25.3Page 416
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The Gut

• Region where food is digested and then absorbed
• Saclike gut
• One opening for taking in food and expelling
  waste
• Complete digestive system
• Opening at both ends mouth and anus

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Body Cavities - Acoelomate
epidermis
gut cavity
no body cavity region between gut and body wall
packed with organs
Figure 25.4aPage 417
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Body Cavities - Pseudocoel
epidermis
gut cavity
unlined body cavity (pseudocoel) around gut
Figure 25.4bPage 417
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Body Cavities - Coelom
gut cavity
peritoneum
lined body cavity (coelom)
Figure 25.4cPage 417
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Segmentation

• Repeating series of body units
• Units may or may not be similar to one another
• Earthworms - segments appear similar
• Insects - segments may be fused and/or have
  specialized functions

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Animal Origins

• Originated during the Precambrian (1.2 billion -
  670 million years ago)
• From what? Two hypotheses
• Multinucleated ciliate became compartmentalized
• Cells in a colonial flagellate became specialized

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Phylum Placozoa

• One living species, Tricoplax adherens
• Simplest known animal
• Two-layer body, 3 mm across

Figure 25.5Page 418
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Sponges - Phylum Porifera

• No symmetry
• No tissues
• No organs
• Reproduce sexually
• Microscopic swimming larval stage

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Sponge Structure
water out
glasslike structural elements
amoeboid cell
pore
central cavity
semifluid matrix
flattened surface cells
water in
Figure 25.7aPage 419
flagellum
microvilli
nucleus
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Phylum Cnidaria

• Only animals that produce nematocysts
• Nerve net
• Hydrostatic skeleton
• Saclike gut

capsules lid at free surface of epidermal cell
trigger
barbed thread inside capsule
Figure 25.8Page 420
nematocyst
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Cnidarian Diversity

• Scyphozoans
• Jellyfish
• Anthozoans
• Sea anemones
• Corals
• Hydrozoans

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Two Main Body Plans
Polyp
outer epithelium (epidermis)
mesoglea (matrix)
Medusa
inner epithelium (gastrodermis)
Figure 25.9 Page 420
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Obelia Life Cycle (Hydrozoan)
male medusa
female medusa
reproductive polyp
sperm
ovum
zygote
feeding polyp
polyp forming
planula
Figure 25.10Page 421
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Flatworms Phylum Platyhelminthes

• Acoelomate, bilateral, cephalized animals
• All have simple or complex organ systems
• Most are hermaphrodites

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Three Classes

• Turbellarians (Turbellaria)
• Flukes (Trematoda)
• Tapeworms (Cestoda)

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Planarian Organ Systems
flame cell
nucleus
pharynx
cilia
protonephridia
fluid filters through membrane folds
opening of tubule at body surface
flame cell
Fig. 25.11a,bPage 422
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Planarian Organ Systems
brain
nerve cord
oviduct
genital pore
ovary
testis
penis
Fig. 25.11cdPage 422
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Roundworms (Nematoda)

• False coelom
• Complete digestive system

gonad
pharynx
intestine
eggs in uterus
anus
false coelom
muscularized body wall
Figure 25.13Page 423
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Flukes Class Trematoda

• Parasitic worms
• Complicated life cycle
• Larval stage infects a mollusk
• Adult infects a vertebrate

Worms mate in human host
Larvae bore into human skin
Larvae form, leave snail
Fertilized egg
Asexual reproduction in intermediate host
Ciliated larva
Figure 25.14Page 424
Southeast Asian blood fluke
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Tapeworms Class Cestoda
Definitive host
Larvae encysted in muscle tissue
Scolex attaches to host intestinal wall
Figure 25.15Page 424
Intermediate host
Mature proglottid with fertilized eggs
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Rotifers

• Bilateral
• Cephalized
• False coelom
• Crown of cilia at head end
• Complete gut

Figure 25.17Page 425
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Two Coelomate Lineages

• Deuterostomes
• Echinoderms
• Chordates

• Protostomes
• Mollusks
• Annelids
• Arthropods

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Cleavage Patterns
Protostome embryo (spiral cleavage)
Deuterostome embryo (radial cleavage)
In-text figurePage 426
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Mollusks Phylum Mollusca

• Bilateral, soft-bodied, coelomate
• Most have a shell or reduced version of one
• Mantle drapes over body and secretes shell
• Most have a fleshy foot
• Many have a radula for shredding food

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Molluscan Diversity

• Gastropods
• Chitins
• Bivalves
• Cephalopods

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Torsion

• Twisting of body parts during larval development
• Occurs only in gastropods

mouth
gill
anus
Figure 25.18Page 426
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Body Plan of a Snail
heart
mantle cavity
gill
anus
mantle
digestive gland
foot
Figure 25.18Page 426
radula
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Body Plan of a Clam
left mantle
mouth
retractor muscle
retractor muscle
foot
shell
left gill
palps
Figure 25.21Page 429
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Cephalopods

• Only the nautilus retains external shell
• Other cephalopods are streamlined, active
  swimmers
• All move by jet propulsion
• Water is forced out of mantle cavity through a
  funnel-shaped siphon
• Have large brains relative to body size

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Cuttlefish Body Plan

• Closed circulatory system with heart and
  accessory heart

esophagus
Figure 25.22Page 429
stomach
kidney
digestive gland
brain
arm
jaw
mantle
reproductive organ
internal shell
siphon
ink sac
heart
accessory heart
tentacle
radula
anus
gill
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Annelids Phylum Annelida

• Segmented, coelomate worms
• Class Polychaeta
• Class Oligochaeta
• Class Hirudinea

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Polychaetes
jaws
toothlike structures

• Most are marine
• Bristles extend from paired, fleshy parapods on
  each segment
• Head end is specialized

pharynx (everted)
antenna
palp (food handling)
tentacle
eyes
chemical-sensing pit
parapod
Fig. 25.24cPage 430
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Leeches - Class Hirudinea

• Predators and parasites
• Less obvious body segmentation
• Most have sharp jaws

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Earthworm - An Oligochaete

• No parapodia, few bristles per segment

Nerve cord
Dorsal blood vessel
Circular muscle
Coelom
Longitudinal muscle
Nephridium
Figure 25.25aPage 431
Seta (retracted)
Nerve cord
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Earthworm Nephridium
bladderlike storage region of nephridium
nephridiums thin loop reabsorbs some solutes,
relinquishes them to blood
blood vessels
body wall
Figure 25.25bPage 431
external pore (fluid containing wastes discharged
here)
funnel (coelomic fluid with waste enters here)
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Earthworm Circulatory System
Hearts
Figure 25.25cPage 431
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Earthworm Digestive System
Coelomic chambers
Crop
Gizzard
Esophagus
Pharynx
Mouth
Figure 25.25dPage 431
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Earthworm Nervous System
Brain
Figure 25.25ePage 431
Nerve cord
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Arthropods Phylum Arthropoda

• The phylum with the greatest number of species
• Four lineages
• Trilobites (all extinct)
• Chelicerates (spiders, mites, scorpions)
• Crustaceans (crabs, shrimps, barnacles)
• Uniramians (insects, centipedes, millipedes)

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Adaptations for Success

• Hardened exoskeleton
• Jointed appendages
• Fused and modified segments
• Respiratory structures
• Specialized sensory structures
• Division of labor

Do not post on Internet
Figure 25.26Page 432
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Chelicerates

• Originated in seas
• A few are still marine horseshoe crabs, sea
  spiders
• The arachnids are all terrestrial
• Spiders Mites
• Scorpions Chiggers
• Daddy longlegs Ticks

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Body Plan of a Spider
eye
Malpighian tubule
digestive gland
heart
brain
poison gland
book lung
ovary
silk gland
anus
mouth
sperm receptacle
spinners
pedipalp
chelicera
Figure 25.28Page 433
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Crustaceans
Copepods Crayfish Barnacles Lobsters
Shrimps Crabs Isopods (pillbugs)

• Most are marine, some freshwater, a few
  terrestrial
• Head has two pairs of antenna, three pairs of
  food-handling appendages

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Lobster Body Plan
one of two eyes
segments of abdomen
fused segments of cephalothorax
antennae (two pairs)
food-handling appendages (three pairs)
tail fin
swimmerets
first leg
Figure 25.29aPage 434
five walking legs (five pairs total)
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Crab Life Cycle
Larval and juvenile stages molt repeatedly and
grow in size
egg
Figure 25.30Page 435
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Millipedes and Centipedes

• Segmented bodies with many legs
• Millipedes
• Two pairs of legs per segment
• Scavengers
• Centipedes
• Flattened, with one pair of legs per segment
• Predators

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Insect Body Plan

• Thorax usually has three pairs of legs and one or
  two pairs of wings
• Abdomen contains most internal organs and
  specialized structure for reproduction
• Three-part gut
• Malpighian tubules attach to midgut and serve in
  elimination of wastes

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Insect Headparts
Butterfly
Mosquito
Grasshopper
antenna
labrum
mandible
Fly
maxilla
palps
labium
Figure 25.32Page 436
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Insect Diversity

• The only winged invertebrates
• More than 800,000 known species
• Most successful species are small in size and
  have a great reproductive capacity

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Types ofInsect Development
Growth and molting
adult
young
egg
Incomplete metamorphosis
Different stages exploit different resources at
different times
egg
adult
nymphs
Complete metamorphosis
adult
egg
pupa
larvae
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Unwelcome Arthropods

• Poisonous spiders
• Disease-carrying ticks
• Venomous scorpions
• Agricultural pests

Do not post on Internet
Corn rootworm (Diabrotica virgifera)
Figure 25.38Page 439
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Echinoderms

• Deuterostomes
• Body wall has spines or plates
• No brain
• Adults are radial with bilateral features

Do not post photos on Internet
Sea urchin
Sea cucumber
Figure 25.39Page 440
Brittle star
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Echinoderm Diversity

• Crinoids (sea lilies and feather stars)
• Sea stars
• Brittle stars
• Sea urchins, heart urchins, sand dollars
• Sea cucumbers

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Body Plan of a Sea Star
sieve plate
coelom
gonad
anus
upper stomach
lower stomach
digestive gland
eyespot
Figure 25.40aPage 441
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Water Vascular System
sieve plate
ampulla
Figure 25.40bPage 441