Download Chapter 23 Major Invertebrate Groups

Biology
Concepts and Applications | 9e
Starr | Evers | Starr
Chapter 23
Major Invertebrate Groups
© Cengage Learning 2015
© Cengage Learning 2015
23.1 How Have Animal Body Plans
Evolved?
• Animals: multicelled heterotrophs whose
unwalled body cells are typically diploid
– Most animals ingest food and digest it inside
their body
– Nearly all are motile
• Invertebrates: animals that lack a
backbone
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How Have Animal Body Plans Evolved?
(cont’d.)
Sponges
Cnidarians
Flatworms
Annelids
5
Mollusks
4
2
Multicellularity
Ancestral protist
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Arthropods
Protostome Development
3 Radial Symmetry
1
Roundworms
Tissues
Bilateral Symmetry
6
Echinoderms
Chordates
Deuterostome Development
How Have Animal Body Plans Evolved?
(cont’d.)
• All animals are multicellular and constitute
the clade Metazoa
– Some animals are aggregations of cells (e.g.,
sponges)
– Most modern animals have cells organized as
tissues
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How Have Animal Body Plans Evolved?
(cont’d.)
• Embryos of jellies and other cnidarians
have two tissue layers: outer ectoderm
and inner endoderm
• Most embryonic cells typically rearrange
themselves to form a middle tissue layer
called mesoderm
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How Have Animal Body Plans Evolved?
(cont’d.)
ectoderm
mesoderm
endoderm
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How Have Animal Body Plans Evolved?
(cont’d.)
• Jellies, sea anemones, and other
cnidarians have radial symmetry: body
parts are repeated around a central axis
• Animals with a three-layer body plan
typically have bilateral symmetry: each
side of body is a mirror image
– Such lineages typically undergo cephalization:
nerve cells and sensory structures become
concentrated at the front of the body
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How Have Animal Body Plans Evolved?
(cont’d.)
• Protostomes: lineage of bilateral animals
in which the first opening on the embryo
surface develops into a mouth
• Deuterostomes: lineage of bilateral
animals in which the second opening on
the embryo surface develops into a mouth
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How Have Animal Body Plans Evolved?
(cont’d.)
• A mass of tissues and organs surrounds
the flatworm gut
• Most bilateral animals have a fluid-filled
body cavity around their gut
– Pseudocoelom: unlined body cavity around
the gut
– Coelom: body cavity lined with tissue derived
from mesoderm; most typical for bilateral
animals
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ANIMATION: Types of Body Cavities
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How Have Animal Body Plans Evolved?
(cont’d.)
• Most bilaterally symmetrical animals have
some degree of segmentation
– Segmentation: a division of a body into similar
units repeated one after the other along the
main axis
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23.2 Animal Origins and Early Radiations
• Colonial theory of animal origins: the first
animals evolved from a colonial protist
– At first, all cells in the colony performed the
same functions
– Eventually, mutations produced cells that
specialized in some tasks and did not carry
out others
– Choanoflagellates are modern protists most
closely related to animals
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Early Evolution
• Early animals were likely similar to
placozoans
– Tiny marine animals having a simple
asymmetrical body and a small genome
• Sponges are another ancient group
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Early Evolution (cont’d.)
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Early Evolution (cont’d.)
• A collection of 570-million-year-old fossils
(called Ediacarans) provide evidence of
early animal diversification
– Ediacarans include a variety of soft-bodied
organisms that may have been early marine
invertebrates
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Early Evolution (cont’d.)
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An Explosion of Diversity
• 542–488 million years ago: Animals
underwent a dramatic adaptive radiation
during the Cambrian period
• What caused this Cambrian explosion in
diversity?
– Rising oxygen levels and changes in global
climate
– The break up of supercontinents
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23.3 Sponges
• Sponges (phylum Porifera): aquatic
animals with a porous body that does not
have tissues
– Flat, nonflagellated cells cover a sponge’s
outer surface
– Flagellated collar cells line the inner surface
– Jellylike extracellular matrix lies in between
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ANIMATION: Body Plan of a Sponge
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Sponges (cont’d.)
• A typical sponge is a suspension feeder
– Eats material filtered from the surrounding
water
• Most sponges are hermaphrodites
– Releases sperm but holds onto eggs
– Fertilization produces a zygote that develops
into a ciliated larva (sexually immature stage)
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Sponges (cont’d.)
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23.4 What Are Cnidarians?
• Cnidarians (phylum Cnidaria): radially
symmetrical, mostly marine animals
– Examples: sea anemones and jellies
• Have a two-layered body, with an outer
layer derived from ectoderm, and an inner
layer from endoderm
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What Are Cnidarians? (cont’d.)
• There are two basic cnidarian body plans,
both with a tentacle-ringed mouth
– Medusae: dome-shaped, with a mouth on the
dome’s lower surface
– Polyps: upward-facing mouth atop a
cylindrical body that is typically attached to a
surface
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ANIMATION: Cnidarian Body Plans
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What Are Cnidarians? (cont’d.)
• Cnidarians are predators
– Their tentacles have cnidocytes: specialized
stinging cells that help them capture prey
– Cnidocytes contain nematocysts: barbed
thread that delivers a dose of venom
– Tentacles move captured food to the mouth,
which opens to a gastrovascular cavity
• Facilitates gas exchange and extracellular
digestion
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ANIMATION: Nematocyst Action
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What Are Cnidarians? (cont’d.)
• Cnidarians are brainless, but
interconnecting nerve cells extend through
their tissues as a nerve net
– Decentralized mesh of nerve cells that allows
movement in cnidarians via contractile cells
• A fluid-filled cavity that contractile cells
exert force against is called a hydrostatic
skeleton
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What Are Cnidarians? (cont’d.)
• Most cnidarians are solitary, but colonial
groups exist
• Coral reefs are built by colonies of polyps
enclosed in a skeleton of secreted calcium
carbonate
– Photosynthetic dinoflagellates live inside each
polyp’s tissues
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What Are Cnidarians? (cont’d.)
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23.5 What Is a Flatworm?
• Flatworms (phylum Platyhelminthes) are
the simplest protostomes
– Flattened body with an array of organ
systems
– No body cavity other than a gastrovascular
cavity
– Rely entirely on diffusion to move nutrients
and gases through their body
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Free-Living Flatworms
• Free-living flatworms: glide along,
propelled by the action of cilia
• Planarians are free-living flatworms
common in ponds
– Highly branched gastrovascular cavity
– Head with chemical receptors and eyespots
– System of tubes to regulate internal water and
solute levels
– Sexual and asexual reproduction
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Free-Living Flatworms (cont’d.)
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ANIMATION: Planarian organ systems
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Parasitic Flatworms
• Flukes and tapeworms are parasitic
flatworms whose life cycle often involves
multiple hosts
– Larvae reproduce asexually in intermediate
hosts
– Adults reproduce sexually in a final or
definitive host
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ANIMATION: Tapeworm life cycle
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23.6 What Are Annelids?
• Annelids (phylum Annelida): bilateral
worms with a coelom and conspicuous
segmentation, inside and out
– They have a tubular gut and a closed
circulatory system, where blood flows through
a continuous system of vessels
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Marine Polychaetes
• Polychaetes are mostly marine
– Bristleworms or sandworms: use chitinhardened jaws to capture prey
– Fan worms and feather duster worms: live in
a tube that they make from sand grains and
mucus
• Head end protrudes from the tube and has
elaborate tentacles to capture food
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Marine Polychaetes (cont’d.)
A
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B
Leeches
• A leech lacks bristles and has a sucker at
either end of its body
• A typical leech is a scavenger or preys on
small invertebrates
• An infamous minority attach to a
vertebrate, pierce its skin, and suck blood
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Leeches (cont’d.)
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Earthworms (cont’d.)
• Each segment of an earthworm contains a
coelomic chamber full of organs
• A gut, ventral nerve cord, and dorsal and
ventral blood vessels run through all
coelomic chambers
• Earthworms are hermaphrodites, but they
cannot fertilize themselves
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ANIMATION: Earthworm body plan
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23.7 What Are Mollusks?
• Mollusks (phylum Mollusca): bilaterally
symmetrical invertebrates with a reduced
coelom
• All have a mantle, which is a skirtlike
extension of the upper body wall that
covers a mantle cavity
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What Are Mollusks? (cont’d.)
anus
gill
excretory organ
heart
mantle
cavity
digestive
gland
stomach
shell
edge of mantle
that covers organs
radula
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foot
What Are Mollusks? (cont’d.)
• Three main groups of mollusks:
– Gastropods: lower body is a broad “foot”
• Examples: snail, slugs, nudibranchs (sea snails)
– Bivalves: has a hinged two-part shell
• Examples: mussels, oysters, clams, and scallops
– Cephalopods: predatory; has a closed
circulatory system; moves by jet propulsion
• Examples: squids, nautiluses, octopuses, cuttlefish
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What Are Mollusks? (cont’d.)
A
B
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C
What Are Mollusks? (cont’d.)
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What Are Mollusks? (cont’d.)
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23.8 What Are Roundworms?
• Roundworms (nematodes, phylum
Nematoda): cylindrical worms with a
pseudocoelom
– Tubular digestive system, excretory organs,
and a nervous system, but no circulatory or
respiratory organs
– Cuticle periodically molts (sheds and
replaces) as they grow
– Some roundworms are parasitic
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ANIMATION: Roundworm body plan
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What Are Roundworms? (cont’d.)
A
B
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C
23.9 What Are Arthropods?
• Arthropods (phylum Arthropoda):
bilaterally symmetrical invertebrates with a
tubular gut, an open circulatory system,
and a reduced coelom
– Examples: spiders, lobsters, barnacles,
centipedes, and insects
• Trilobites, a now-extinct arthropod lineage,
were the most abundant and diverse
animal group in Cambrian seas
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What Are Arthropods? (cont’d.)
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What Are Arthropods? (cont’d.)
• Features of arthropods:
– Exoskeleton: hard external parts that muscles
attach to and move
– Compound eyes: motion-sensitive eyes
– Antennae: sensory structure on the head that
detects touch and odors
• Most arthropods undergo metamorphosis
– A dramatic change in form between the larval
stage and the adult
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23.10 What Are the Main Kinds of
Arthropods?
• Chelicerates: have specialized feeding
structures (chelicerae) and no antennae
– Examples: arachnids and horseshoe crabs
• Myriapods: long-bodied terrestrial; one
pair of antennae; many similar segments
– Examples: centipedes and millipedes
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What Are the Main Kinds of Arthropods?
(cont’d.)
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What Are the Main Kinds of Arthropods? (cont’d.)
B
cephalothorax
abdomen
C
D
A
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Video: Millipede
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What Are the Main Kinds of Arthropods?
(cont’d.)
• Crustaceans: mostly marine arthropods
with a calcium-hardened cuticle and two
pairs of antennae
– Examples: lobsters, crabs, krill, and barnacles
• Insects (covered in next section): likely
descended from freshwater crustaceans
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What Are the Main Kinds of Arthropods?
(cont’d.)
A
B
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C
23.11 What Makes Insects So Diverse and
Important?
• Insects: most diverse arthropod group
– More than a million named species
– Live on every continent
– Insects have six legs, two antennae, and
sometimes wings
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Characteristics of Insects
• Insects have a three-part body plan:
– Head: one pair of antennae and two
compound eyes
– Thorax: contains one or two pairs of wings
• Tubular gut and an open circulatory system
– Abdomen: contains digestive organs, sex
organs, and water-conserving excretory
organs
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Characteristics of Insects (cont’d.)
antenna
compound
eye
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head
thorax
abdomen
Characteristics of Insects
• Most modern insects have wings and
undergo metamorphosis
– With complete metamorphosis, a larva grows
and molts without altering its form, then
undergoes pupation
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Characteristics of Insects (cont’d.)
Larva
(leaf-eating,
wingless caterpillar)
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Pupa
(remodeling
stage)
Adult
(winged
nectar feeder)
Insect Ecology
• Insects play essential roles in just about
every land ecosystem
– Interactions between pollinating insects and
flowering plant likely increased diversity
– Insects serve as food for a variety of wildlife
– Insects dispose of wastes and remains
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Insect Ecology (cont’d.)
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23.12 What Are Echinoderms?
• Echinoderms (phylum Echinodermata):
have interlocking spines and plates of
calcium carbonate in their body wall
– Begin life as bilateral free-swimming larvae,
then develop into radially symmetrical adults
with five parts
– Sea stars (also called starfish) are the most
familiar echinoderms
– Water–vascular system: system of fluid-filled
tubes and tube feet that function in locomotion
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What Are Echinoderms? (cont’d.)
upper
stomach anus
spine
gonad
lower
stomach
coelom
digestive gland
eyespot
spine
ossicle (tiny
skeletal structure)
ampullae
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tube feet
What Are Echinoderms? (cont’d.)
A
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B
C