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Chapter 33
Invertebrates
PowerPoint TextEdit Art Slides for
Biology, Seventh Edition
Neil Campbell and Jane Reece
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Figure 33.1 A Christmas tree worm, a marine invertebrate
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Chordata
Echinodermata
Other bilaterians (including
Nematoda, Arthropoda,
Mollusca, and Annelida)
Cnidaria
Porifera
Figure 33.2 Review of animal phylogeny
Deuterostomia
Bilateria
Eumetazoa
Ancestral colonial
choanoflagellate
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Figure 33.4 Anatomy of a sponge
5 Choanocytes. The spongocoel
is lined with feeding cells called
choanocytes. By beating flagella,
the choanocytes create a current that
draws water in through the porocytes.
Azure vase sponge (Callyspongia
plicifera)
4 Spongocoel. Water
passing through porocytes
enters a cavity called the
spongocoel.
Flagellum
Food particles
Collar in mucus
Osculum
Phagocytosis of
food particles
3 Porocytes. Water enters
the epidermis through
channels formed by
porocytes, doughnut-shaped
cells that span the body wall.
Spicules
2 Epidermis. The outer
layer consists of tightly
packed epidermal cells.
Choanocyte
Water
flow
1 Mesohyl. The wall of this
simple sponge consists of
two layers of cells separated
by a gelatinous matrix, the
mesohyl (“middle matter”).
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Amoebocyte
6 The movement of the choanocyte
flagella also draws water through its
collar of fingerlike projections. Food
particles are trapped in the mucus
coating the projections, engulfed by
phagocytosis, and either digested or
transferred to amoebocytes.
7 Amoebocyte. Amoebocytes
transport nutrients to other cells of
the sponge body and also produce
materials for skeletal fibers (spicules).
Those Poor Lonely Invertebrates
Nobody
loves me!!!
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Activity
• Create a personal ad for a poor invertebrate
that is desperate for a date
• First list the characteristics of a phyla
given to you by using your textbook
• Then write a personal ad but be sure to
include ALL of the characteristics from the list
you made
• You will be assigned two phyla
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Figure 33.5 Polyp and medusa forms of cnidarians
Polyp
Medusa
Mouth/anus
Tentacle
Gastrovascular
cavity
Gastrodermis
Mesoglea
Body
stalk
Epidermis
Tentacle
Mouth/anus
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Figure 33.7 Cnidarians
(a) These colonial polyps are members of
class Hydrozoa.
(b) Many species of jellies (class
Scyphozoa), including the
species pictured here, are
bioluminescent. The largest
scyphozoans have tentacles
more than 100 m long
dangling from a bell-shaped
body up to 2 m in diameter.
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(c) The sea wasp (Chironex
fleckeri) is a member of
class Cubozoa. Its poison,
which can subdue fish and
other large prey, is more
potent than cobra venom.
(d) Sea anemones and other
members of class Anthozoa
exist only as polyps.
Figure 33.9 A marine flatworm (class Turbellaria)
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Figure 33.10 Anatomy of a planarian, a turbellarian
Pharynx. The mouth is at the
tip of a muscular pharynx that
extends from the animal’s
ventral side. Digestive juices
are spilled onto prey, and the
pharynx sucks small pieces of
food into the gastrovascular
cavity, where digestion continues.
Digestion is completed within
the cells lining the gastrovascular cavity, which has
three branches, each with
fine subbranches that provide an extensive surface area.
Undigested wastes
are egested
through the mouth.
Gastrovascular
cavity
Eyespots
Ganglia. Located at the anterior end
of the worm, near the main sources
of sensory input, is a pair of ganglia,
dense clusters of nerve cells.
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Ventral nerve cords. From
the ganglia, a pair of
ventral nerve cords runs
the length of the body.
Figure 33.12 Anatomy of a tapeworm
Proglottids with
reproductive structures
200 µm
Scolex
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Hooks
Sucker
Figure 33.13 A rotifer
0.1 mm
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Figure 33.16 The basic body plan of a mollusc
Nephridium. Excretory organs
called nephridia remove metabolic
wastes from the hemolymph.
Heart. Most molluscs have an open circulatory
system. The dorsally located heart pumps
circulatory fluid called hemolymph through arteries
into sinuses (body spaces). The organs of the
mollusc are thus continually bathed in hemolymph.
The long digestive tract is
coiled in the visceral mass.
Visceral mass
Coelom
Intestine
Gonads
Mantle
Mantle
cavity
Stomach
Shell
Radula
Anus
The nervous
system consists
of a nerve ring
around the
esophagus, from
which nerve
cords extend.
Gill
Foot
Nerve
cords
Esophagus
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Mouth
Mouth
Radula. The mouth
region in many
mollusc species
contains a rasp-like
feeding organ
called a radula. This
belt of backwardcurved teeth slides
back and forth,
scraping and
scooping like a
backhoe.
Figure 33.21 Anatomy of a clam
Hinge area
Mantle
Gut
Coelom
Heart
Shell
Adductor
muscle
Mouth
Anus
Excurrent
siphon
Palp
Water
flow
Foot
Mantle
cavity
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Gill
Incurrent
siphon
Figure 33.23 Anatomy of an earthworm
Chaetae. Each segment
has four pairs of
chaetae, bristles that
provide traction for
burrowing.
Cerebral ganglia. The
earthworm nervous system
features a brain-like pair of
cerebral ganglia above and
in front of the pharynx. A ring
of nerves around the pharynx
connects to a subpharyngeal
ganglion, from which a fused
pair of nerve cords runs
posteriorly.
Epidermis
Cuticle
Circular
muscle
Many of the internal
structures are repeated
within each segment of
the earthworm.
Metanephridium. Each
segment of the worm
contains a pair of
excretory tubes, called
metanephridia, with
ciliated funnels, called
Septum
nephrostomes. The
(partition
metanephridia remove
between
wastes from the blood
segments) and coelomic fluid
through exterior pores.
Coelom. The coelom
of the earthworm is
partitioned by septa.
Each segment is surrounded by longitudinal muscle, which in
turn is surrounded by circular muscle. Earthworms coordinate
the contraction of these two sets of muscles to move (see
Figure 49.25). These muscles work against the noncompressible
coelomic fluid, which acts as a hydrostatic skeleton.
Longitudinal
muscle
Dorsal
vessel
Anus
Intestine
Nerve
cords
Tiny blood vessels are
abundant in the earthworm’s
skin, which functions as its
respiratory organ. The blood
contains oxygen-carrying
hemoglobin.
Ventral
vessel
Nephrostome Clitellum
Pharynx Esophagus
Metanephridium
Crop
Giant Australian earthworm
Intestine
Gizzard
Mouth
Subpharyngeal
ganglion
Ventral nerve cords with segmental ganglia.
The circulatory system, a network of vessels,
The nerve cords penetrate the septa and run
is closed. The dorsal and ventral vessels are
the length of the animal, as do the digestive
linked by segmental pairs of vessels. The dorsal
tract and longitudinal blood vessels.
vessel and five pairs of vessels that circle the esophagus
of an earthworm are muscular and pump blood through
the circulatory system.
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Figure 33.29 External anatomy of an arthropod
Cephalothorax
Antennae
(sensory
reception)
Abdomen
Head Thorax
Swimming
appendages
Walking legs
Pincer (defense)
Mouthparts (feeding)
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Figure 33.35 Anatomy of a grasshopper, an insect
The insect body has three regions: head,
thorax, and abdomen. The segmentation
of the thorax and abdomen are obvious,
but the segments that form the head are fused.
Abdomen
Thorax Head
Compound eye
Cerebral ganglion. The two nerve
Heart. The
cords meet in the head, where the
insect heart
ganglia of several anterior segments
drives hemolymph are fused into a cerebral ganglion
through an
(brain). The antennae, eyes, and
open circulatory
other sense organs are concentrated
system.
on the head.
Antennae
Ovary
Malpighian tubules.
Anus
Metabolic wastes are
removed from the
Vagina
hemolymph by excretory
organs called Malpighian
tubules, which are outpocketings of the
digestive tract.
Tracheal tubes. Gas exchange in insects is
accomplished by a tracheal system of branched,
chitin-lined tubes that infiltrate the body and
carry oxygen directly to cells. The tracheal
system opens to the outside of the body
through spiracles, pores that can control air
flow and water loss by opening or closing.
Nerve cords. The insect
nervous system
consists of a pair of
ventral nerve cords
with several
segmental ganglia.
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Dorsal
artery
Crop
Insect mouthparts are formed from
several pairs of modified appendages.
The mouthparts include mandibles,
which grasshoppers use for chewing.
In other insects, mouthparts are
specialized for lapping, piercing, or
sucking.
Figure 33.40 Echinoderms
(a) A sea star (class Asteroidea)
(c) A sea urchin (class Echinoidea)
(e) A sea cucumber (class Holothuroidea)
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(b) A brittle star (class Ophiuroidea)
(d) A feather star (class Crinoidea)
(f) A sea daisy (class Concentricycloidea)
Figure 33.39 Anatomy of a sea star, an echinoderm
A short digestive tract runs from the
mouth on the bottom of the central
disk to the anus on top of the disk.
Central disk. The central
disk has a nerve ring and
nerve cords radiating from
the ring into the arms.
Spine
Stomach
Anus
The surface of a sea star is
covered by spines that help
defend against predators, as
well as by small gills that
provide gas exchange.
Gills
Madreporite. Water can flow
in or out of the water vascular
system into the surrounding
water through the madreporite.
Digestive glands secrete
digestive juices and aid in
the absorption and storage
of nutrients.
Gonads
Ring
canal
Radial
nerve
Ampulla
Podium
Tube
feet
Radial canal. The water vascular
system consists of a ring canal in the
central disk and five radial canals,
each running in a groove down the
entire length of an arm.
Branching from each radial canal are hundreds of hollow, muscular tube
feet filled with fluid. Each tube foot consists of a bulb-like ampulla and
suckered podium (foot portion). When the ampulla squeezes, it forces
water into the podium and makes it expand. The podium then
contacts the substrate. When the muscles in the wall of the podium
contract, they force water back into the ampulla, making the podium
shorten and bend.
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Table 33.7 Selected Animal Phyla
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