Animals: The Invertebrates

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Animals The Invertebrates

• Chapter 23

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Characteristics of Animals

• Multicelled heterotrophic eukaryotes that ingest
  or parasitize other organisms.
• Require oxygen for aerobic respiration
• Reproduce sexually, and perhaps asexually
• Motile at some stage
• Develop from embryos
• Almost all have tissues, organs and organ
  systems.
• Animals originate during late precambrian.

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Major Animal Phyla
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Symmetry
Radial
Bilateral
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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
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Body Cavities - Pseudocoel
epidermis
gut cavity
unlined body cavity (pseudocoel) around gut
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Body Cavities - Coelom
gut cavity
peritoneum
lined body cavity (coelom)
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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

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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
flagellum
microvilli
nucleus
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Phylum Cnidaria

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

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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)
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Obelia Life Cycle (Hydrozoan)
male medusa
female medusa
reproductive polyp
sperm
ovum
zygote
feeding polyp
polyp forming
planula
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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
brain
nerve cord
oviduct
genital pore
ovary
testis
penis
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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
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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
Cilated larva
Southeast Asian blood fluke
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Tapeworms Class Cestoda
Definitive host
Larvae encysted in muscle tissue
Scolex attaches to host intestinal wall
Intermediate host
Mature proglottid with fertilized eggs
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Roundworms (Nematoda)

• False coelom
• Complete digestive system

gonad
pharynx
intestine
eggs in uterus
anus
false coelom
muscularized body wall
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Two Coelomate Lineages

• Protostomes
• Mollusks
• Annelids
• Arthropods

• Deuterostomes
• Echinoderms
• Chordates

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Cleavage Patterns
Protostome embryo (spiral cleavage)
Deuterostome embryo (radial cleavage)
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First Opening in Embryo
pouch will form mesoderm around coelom
protostome
developing gut
coelom
solid mass of mesoderm
deuterostome
developing gut
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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
• Chitons
• Bivalves
• Cephalopods

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Torsion

• Twisting of body parts during larval development
• Occurs only in gastropods
• Before torsion head faces forward and anus faces
  backward
• After torsion anus is positioned over head

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Body Plan of a Snail
heart
mantle cavity
mouth
anus
gill
gill
anus
mantle
digestive gland
foot
radula
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Body Plan of a Clam
left mantle
mouth
retractor muscle
retractor muscle
foot
shell
left gill
palps
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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

digestive gland
stomach
radula
brain
shell
siphon
reproductive organ
accessory heart
anus
heart
gill
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Annelids Phylum Annelida

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

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Polychaetes

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

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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
Seta (retracted)
Nerve cord
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Earthworm Circulatory System
Hearts
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Earthworm Digestive System
Coelomic chambers
Crop
Gizzard
Esophagus
Pharynx
Mouth
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Earthworm Nervous System
Brain
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

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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
Malpighian tubule
heart
brain
book lung
anus
silk gland
pedipalp
chelicera
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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
five walking legs (five pairs total)
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Crab Life Cycle
Larval and juvenile stages molt repeatedly and
grow in size
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Millipedes and Centipedes

• Segmented bodies with many legs
• Millipedes
• Two pairs of legs per segment
• Scavengers
• Centipedes
• Flattened with one pairs 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
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Insect Diversity

• Insects are the only winged invertebrates
• There are 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
nymphs
egg
adult
Complete metamorphosis
adult
larvae
egg
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Echinoderms

• Deuterostomes
• Almost all are marine
• Body wall has spines or plates of calcium
  carbonate
• No brain
• Adults are radial with bilateral features

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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
gonad
coelom
anus
upper stomach
lower stomach
digestive gland
eyespot
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Water Vascular System
sieve plate
ampulla