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Chapter 33
Invertebrates
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Overview: Life Without a Backbone
• Invertebrates
– Are animals that lack a backbone
– Account for 95% of known animal species
Figure 33.1
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Chordata
Echinodermata
Other bilaterians (including
Nematoda, Arthropoda,
Mollusca, and Annelida)
Porifera
Cnidaria
• A review of animal phylogeny
Deuterostomia
Bilateria
Eumetazoa
Ancestral colonial
choanoflagellate
Figure 33.2
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• Exploring invertebrate diversity
PORIFERA (5,500 species)
A sponge
PLACOZOA (1 species)
CNIDARIA (10,000 species)
A jelly
KINORHYNCHA (150 species)
0.5 mm
250 µm
A placozoan (LM) A kinorhynch (LM)
ROTIFERA (1,800 species)
PLATYHELMINTHES (20,000 species)
A marine flatworm
ECTOPROCTA (4,500 species)
Figure 33.3
A rotifer (LM)
PHORONIDA (20 species)
Ectoprocts Phoronids
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• Exploring invertebrate diversity
BRACHIOPODA (335 species)
NEMERTEA (900 species)
A brachiopod
ACANTHOCEPHALA (1,100 species)
A ribbon worm
CTENOPHORA (100 species)
5 mm
An acanthocephalan
A ctenophore, or comb jelly
MOLLUSCA (93,000 species)
ANNELIDA (16,500 species)
An octopus
A marine annelid
PRIAPULA (16 species)
LORICIFERA (10 species)
50 µm
Figure 33.3
A loriciferan (LM)
A priapulan
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• Exploring invertebrate diversity
ARTHROPODA (1,000,000 + species)
NEMATODA (25,000 species)
A roundworm
A scorpion (an arachnid)
CYCLIOPHORA (1 species)
TARDIGRADA (800 species)
100 µm
100 µm
A cycliophoran (colorized SEM) Tardigrades (colorized SEM)
HEMICHORDATA (85 species)
ONYCHOPHORA (110 species)
An onychophoran
An acorn worm
ECHINODERMATA (7,000 species)
Figure 33.3
A sea urchin
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CHORDATA (52,000 species)
A tunicate
• Sponges are sessile and have a porous body
and choanocytes
• Sponges, phylum Porifera
– Live in both fresh and marine waters
– Lack true tissues and organs
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• Sponges are suspension feeders
– Capturing food particles suspended in the
water that passes through their body
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.
3 Porocytes. Water enters
the epidermis through
channels formed by
porocytes, doughnut-shaped
cells that span the body wall.
2 Epidermis. The outer
layer consists of tightly
packed epidermal cells.
Figure 33.4
Flagellum
Collar
Food particles
in mucus
Choanocyte
Osculum
Phagocytosis of
food particles
Spicules
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).
• Choanocytes, flagellated collar cells
– Generate a water current through the sponge
and ingest suspended food
• Most sponges are hermaphrodites
– Meaning that each individual functions as both
male and female
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• Concept 33.2: Cnidarians have radial
symmetry, a gastrovascular cavity, and
cnidocytes
• All animals except sponges
– Belong to the clade Eumetazoa, the animals
with true tissues
• Phylum Cnidaria
– Is one of the oldest groups in this clade
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• Cnidarians
– Have diversified into a wide range of both
sessile and floating forms including jellies,
corals, and hydras
– But still exhibit a relatively simple diploblastic,
radial body plan
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• The basic body plan of a cnidarian
– Is a sac with a central digestive compartment,
the gastrovascular cavity
• A single opening
– Functions as both mouth and anus
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• There are two variations on this body plan
– The sessile polyp and the floating medusa
Polyp
Medusa
Mouth/anus
Tentacle
Gastrovascular
cavity
Gastrodermis
Mesoglea
Body
stalk
Epidermis
Tentacle
Mouth/anus
Figure 33.5
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• Cnidarians are carnivores
– That use tentacles to capture prey
• The tentacles are armed with cnidocytes
– Unique cells that function in defense and the
capture of prey
Prey
Tentacle
“Trigger”
Discharge
Of thread
Nematocyst
Figure 33.6
Coiled thread
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Cnidocyte
• The phylum Cnidaria is divided into four major
classes
Table 33.1
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– Hydrozoa, Scyphozoa, Cubozoa, and
Anthozoa
(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.
Figure 33.7a–d
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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.
Hydrozoans
• Most hydrozoans
– Alternate between polyp and medusa forms
2 Some of the colony’s
polyps, equipped with tentacles,
are specialized for feeding.
3 Other polyps, specialized
for reproduction, lack
tentacles and produce tiny
medusae by asexual budding.
4 The medusae
swim off, grow, and
reproduce sexually.
Reproductive
polyp
1 A colony of
interconnected
polyps (inset,
LM) results
from asexual
reproduction
by budding.
Feeding
polyp
Medusa
bud
MEIOSIS
Gonad
Medusa
SEXUAL
REPRODUCTION
Sperm
Egg
ASEXUAL
REPRODUCTION
(BUDDING)
Portion of
a colony
of polyps
FERTILIZATION
Zygote
Developing
polyp
Mature
polyp
Planula
(larva)
Figure 33.8
1 mm
6 The planula eventually settles
and develops into a new polyp.
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5 The zygote develops into a
solid ciliated larva called a planula.
Key
Haploid (n)
Diploid (2n)
Scyphozoans
• In the class Scyphozoa
– Jellies (medusae) are the prevalent form of the
life cycle
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Cubozoans
• In the class Cubozoa, which includes box
jellies and sea wasps
– The medusa is box-shaped and has complex
eyes
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Anthozoans
• Class Anthozoa includes the corals and sea
anemones
– Which occur only as polyps
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• Concept 33.3: Most animals have bilateral
symmetry
• The vast majority of animal species belong to
the clade Bilateria
– Which consists of animals with bilateral
symmetry and triploblastic development
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Flatworms
• Members of phylum Platyhelminthes
– Live in marine, freshwater, and damp terrestrial
habitats
– Are flattened dorsoventrally and have a
gastrovascular cavity
• Although flatworms undergo triploblastic
development
– They are acoelomates
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• Flatworms are divided into four classes
Table 33.2
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Turbellarian
• Turbellarians
– Are nearly all free-living and mostly marine
Figure 33.9
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• The best-known turbellarians, commonly called
planarians
– Have light-sensitive eyespots and centralized
nerve nets
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
Figure 33.10
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.
Monogeneans and Trematode
• Monogeneans and trematodes
– Live as parasites in or on other animals
– Parasitize a wide range of hosts
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• Trematodes that parasitize humans
– Spend part of their lives in snail hosts
1 Mature flukes live in the blood vessels of the human
intestine. A female fluke fits into a groove running
the length of the larger male’s body, as shown in
the light micrograph at right.
Male
Female
1 mm
5 These larvae penetrate
the skin and blood
vessels of humans
working in irrigated
fields contaminated
with infected human
feces.
2 Blood flukes reproduce
sexually in the human host.
The fertilized eggs exit the
host in feces.
3 The eggs develop in
water into ciliated
larvae. These larvae
infect snails, the
intermediate hosts.
Figure 33.11
4 Asexual reproduction
within a snail results in
another type of motile
larva, which escapes from
the snail host.
Snail host
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• Most monogeneans
– Are parasites of fish
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Tapeworm
• Tapeworms
– Are also parasitic and lack a digestive system
Proglottids with
reproductive structures
200 µm
Scolex
Figure 33.12
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Hooks
Sucker
Rotifers
• Rotifers, phylum Rotifera
– Are tiny animals that inhabit fresh water, the
ocean, and damp soil
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• Rotifers are smaller than many protists
– But are truly multicellular and have specialized
organ systems
Figure 33.13
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0.1 mm
• Rotifers have an alimentary canal
– A digestive tube with a separate mouth and
anus that lies within a fluid-filled pseudocoelom
• Rotifers reproduce by parthenogenesis
– In which females produce more females from
unfertilized eggs
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Lophophorates: Ectoprocts, Phoronids, and Brachiopods
• Lophophorates have a lophophore
– A horseshoe-shaped, suspension-feeding
organ bearing ciliated tentacles
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• Ectoprocts
– Are colonial animals that superficially resemble
plants
Lophophore
(a) Ectoprocts, such as this sea
mat (Membranipora
membranacea), are colonial
Figure 33.14a
lophophorates.
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• Phoronids
– Are tube-dwelling marine worms ranging from
1 mm to 50 cm in length
Lophophore
(b) In phoronids such as
Phoronis hippocrepia, the
lophophore and mouth
are at one end of an
Figure 33.14b
elongated trunk.
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• Brachiopods superficially resemble clams and
other hinge-shelled molluscs
– But the two halves of the shell are dorsal and
ventral rather than lateral, as in clams
Lophophore
(c) Brachiopods have a hinged shell.
The two parts of the shell are
Figure 33.14c
dorsal and ventral.
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Nemerteans
• Members of phylum Nemertea
– Are commonly called proboscis worms or
ribbon worms
Figure 33.15
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• The nemerteans unique proboscis
– Is used for defense and prey capture
– Is extended by a fluid-filled sac
• Nemerteans also have a closed circulatory
system
– In which the blood is contained in vessels
distinct from fluid in the body cavity
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• Concept 33.4: Molluscs have a muscular foot, a
visceral mass, and a mantle
• Phylum Mollusca
– Includes snails and slugs, oysters and clams, and
octopuses and squids
• Most molluscs are marine
– Though some inhabit fresh water and some are
terrestrial
• Molluscs are soft-bodied animals
– But most are protected by a hard shell
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• All molluscs have a similar body plan with three
main parts
– A muscular foot
– A visceral mass
– A mantle
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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
Figure 33.16
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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.
• Most molluscs have separate sexes
– With gonads located in the visceral mass
• The life cycle of many molluscs
– Includes a ciliated larval stage called a
trochophore
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• There are four major classes of molluscs
Table 33.3
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Chitons
• Class Polyplacophora is composed of the
chitons
– Oval-shaped marine animals encased in an
armor of eight dorsal plates
Figure 33.17
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Gastropods
• About three-quarters of all living species of
molluscs
– Belong to class Gastropoda
(a) A land snail
Figure 33.18a, b
(b) A sea slug. Nudibranchs, or sea slugs, lost their shell
during their evolution.
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• Most gastropods
– Are marine, but there are also many
freshwater and terrestrial species
– Possess a single, spiraled shell
• Slugs lack a shell
– Or have a reduced shell
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• The most distinctive characteristic of this class
– Is a developmental process known as torsion,
which causes the animal’s anus and mantle to
end up above its head
Stomach
Mantle
cavity
Anus
Mouth
Figure 33.19
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Intestine
Bivalves
• Molluscs of class Bivalvia
– Include many species of clams, oysters,
mussels, and scallops
– Have a shell divided into two halves
Figure 33.20
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• The mantle cavity of a bivalve
– Contains gills that are used for feeding as well
as gas exchange
Hinge area
Mantle
Gut
Coelom
Heart
Shell
Adductor
muscle
Mouth
Anus
Excurrent
siphon
Palp
Water
flow
Foot
Figure 33.21
Mantle
cavity
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Gill
Incurrent
siphon
Cephalopods
• Class Cephalopoda includes squids and
octopuses
– Carnivores with beak-like jaws surrounded by
tentacles of their modified foot
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• Most octopuses
– Creep along the sea floor in search of prey
Figure 33.22a
(a) Octopuses are considered among the
most intelligent invertebrates.
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• Squids use their siphon
– To fire a jet of water, which allows them to
swim very quickly
Figure 33.22b
(b) Squids are speedy carnivores with
beaklike jaws and well-developed eyes.
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`
• One small group of shelled cephalopods
– The nautiluses, survives today
Figure 33.22c
(c) Chambered nautiluses are the only living
cephalopods with an external shell.
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• Concept 33.5: Annelids are segmented worms
• Annelids
– Have bodies composed of a series of fused
rings
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• The phylum Annelida is divided into three
classes
Table 33.4
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Oligochaetes
• Oligochaetes (class Oligochaeta)
– Are named for their relatively sparse chaetae,
or bristles made of chitin
– Include the earthworms and a variety of
aquatic species
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• Earthworms eat their way through the soil,
extracting nutrients as the soil moves through
the alimentary canal
– Which helps till the earth, making earthworms
valuable to farmers
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• Anatomy of an earthworm
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.
Epidermis
Septum
(partition
between
segments)
Circular
muscle
Many of the internal
structures are repeated
within each segment of
the earthworm.
Chaetae. Each segment
has four pairs of
chaetae, bristles that
provide traction for
burrowing.
Longitudinal
muscle
Dorsal
vessel
Anus
Intestine
Nerve
cords
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.
Cuticle
Metanephridium. Each
segment of the worm
contains a pair of
excretory tubes, called
metanephridia, with
ciliated funnels, called
nephrostomes. The
metanephridia remove
wastes from the blood
and coelomic fluid
through exterior pores.
Nephrostome
Pharynx
Tiny blood vessels are
abundant in the earthworm’s
skin, which functions as its
respiratory organ. The blood
contains oxygen-carrying
hemoglobin.
Ventral
vessel
Clitellum
Esophagus
Metanephridium
Crop
Giant Australian earthworm
Intestine
Gizzard
Mouth
Subpharyngeal
ganglion
Table 33.23
The circulatory system, a network of vessels,
is closed. The dorsal and ventral vessels are linked
by segmental pairs of vessels. The dorsal 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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Ventral nerve cords with segmental ganglia.
The nerve cords penetrate the septa and run
the length of the animal, as do the digestive
tract and longitudinal blood vessels.
Polychaetes
• Members of class Polychaeta
– Possess paddlelike parapodia that function as
gills and aid in locomotion
Parapodia
Figure 33.24
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Leeches
• Members of class Hirudinea
– Are blood-sucking parasites, such as leeches
Figure 33.25
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• Concept 33.6: Nematodes are nonsegmented
pseudocoelomates covered by a tough cuticle
• Among the most widespread of all animals,
nematodes, or roundworms
– Are found in most aquatic habitats, in the soil,
in moist tissues of plants, and in the body
fluids and tissues of animals
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• The cylindrical bodies of nematodes (phylum
Nematoda)
– Are covered by a tough coat called a cuticle
25 µm
Figure 33.26
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• Some species of nematodes
– Are important parasites of plants and animals
Encysted juveniles
Figure 33.27
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Muscle tissue
50 µm
• Concept 33.7: Arthropods are segmented
coelomates that have an exoskeleton and
jointed appendages
• Two out of every three known species of
animals are arthropods
• Members of the phylum Arthropoda
– Are found in nearly all habitats of the
biosphere
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General Characteristics of Arthropods
• The diversity and success of arthropods
– Are largely related to their segmentation, hard
exoskeleton, and jointed appendages
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• Early arthropods, such as trilobites
– Showed little variation from segment to
segment
Figure 33.28
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• As arthropods evolved
– The segments fused, and the appendages
became more specialized
• The appendages of some living arthropods
– Are modified for many different functions
Cephalothorax Abdomen
Antennae
(sensory
reception)
Head Thorax
Swimming
appendages
Walking legs
Figure 33.29
Pincer (defense) Mouthparts (feeding)
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• The body of an arthropod
– Is completely covered by the cuticle, an
exoskeleton made of chitin
• When an arthropod grows
– It molts its exoskeleton in a process called
ecdysis
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• Arthropods have an open circulatory system
– In which fluid called hemolymph is circulated
into the spaces surrounding the tissues and
organs
• A variety of organs specialized for gas
exchange
– Have evolved in arthropods
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• Molecular evidence now suggests
– That living arthropods consist of four major
lineages that diverged early in the evolution of
the phylum
Table 33.5
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Cheliceriforms
• Cheliceriforms, subphylum Cheliceriformes
– Are named for clawlike feeding appendages
called chelicerae
– Include spiders, ticks, mites, scorpions, and
horseshoe crabs
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• Most of the marine cheliceriforms are extinct
– But some species survive today, including the
horseshoe crabs
Figure 33.30
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• Most modern cheliceriforms are arachnids
– A group that includes spiders, scorpions, ticks,
and mites
50 µm
(a) Scorpions have pedipalps that are pincers (b) Dust mites are ubiquitous scavengers in (c) Web-building spiders are generally
specialized for defense and the capture of
human dwellings but are harmless except
most active during the daytime.
food. The tip of the tail bears a poisonous
to those people who are allergic to them
stinger.
(colorized SEM).
Figure 33.31a–c
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• Arachnids have an abdomen and a
cephalothorax
– Which has six pairs of appendages, the most
anterior of which are the chelicerae
Intestine
Digestive
gland
Stomach
Heart
Brain
Eyes
Poison
gland
Ovary
Anus
Book lung
Spinnerets
Figure 33.32
Silk gland
Sperm
Gonopore
(exit for eggs) receptacle
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Chelicera
Pedipalp
Myriapods
• Subphylum Myriapoda
– Includes millipedes and centipedes
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• Millipedes, class Diplopoda
– Have a large number of legs
• Each trunk segment
– Has two pairs of legs
Figure 33.33
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• Centipedes, class Chilopoda
– Are carnivores with jaw-like mandibles
– Have one pair of legs per trunk segment
Figure 33.34
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Insects
• Subphylum Hexapoda, insects and their
relatives
– Are more species-rich than all other forms of
life combined
– Live in almost every terrestrial habitat and in
fresh water
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• The internal anatomy of an insect
– Includes several complex organ systems
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
Heart. The
insect heart
drives hemolymph
through an
open circulatory
system.
Cerebral ganglion. The two nerve
cords meet in the head, where the
ganglia of several anterior segments
are fused into a cerebral ganglion
(brain). The antennae, eyes, and
other sense organs are concentrated
on the head.
Antennae
Ovary
Figure 33.35
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.
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Nerve cords. The insect
nervous system
consists of a pair of
ventral nerve cords
with several
segmental ganglia.
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.
• Flight is obviously one key to the great success
of insects
• An animal that can fly
– Can escape predators, find food, and disperse
to new habitats much faster than organisms
that can only crawl
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• Many insects
– Undergo metamorphosis during their
development
• In incomplete metamorphosis, the young,
called nymphs
– Resemble adults but are smaller and go
through a series of molts until they reach full
size
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• Insects with complete metamorphosis
– Have larval stages specialized for eating and
growing that are known by such names as
maggot, grub, or caterpillar
• The larval stage
– Looks entirely different from the adult stage
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• Metamorphosis from the larval stage to the
adult stage
– Occurs during a pupal stage
(a) Larva (caterpillar)
(b) Pupa
(c) Pupa
(d) Emerging adult
Figure 33.6a–e
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(e) Adult
• Insects are classified into about 26 orders
ORDER
Blattodea
Coleoptera
Dermaptera
Diptera
Hemiptera
Hymenoptera
Isoptera
APPROXIMATE
NUMBER OF
SPECIES
4,000
350,000
1,200
151,000
85,000
125,000
2,000
MAIN CHARACTERISTICS
EXAMPLES
Cockroaches have a dorsoventrally flattened body, with legs
modified for rapid running. Forewings, when present, are
leathery, whereas hind wings are fanlike. Fewer than 40 cockroach species live in houses; the rest exploit habitats ranging
from tropical forest floors to caves and deserts.
German
cockroach
Beetles comprise the most species-rich order of insects. They
have two pairs of wings, one of which is thick and leathery, the
other membranous. They have an armored exoskeleton and
mouthparts adapted for biting and chewing. Beetles undergo
complete metamorphosis.
Japanese
beetle
Earwigs are generally nocturnal scavengers. While some
species are wingless, others have two pairs of wings, one of
which is thick and leathery, the other membranous. Earwigs
have biting mouthparts and large posterior pincers. They undergo incomplete metamorphosis.
Dipterans have one pair of wings; the second pair has become
modified into balancing organs called halteres. Their head is
large and mobile; their mouthparts are adapted for sucking,
piercing, or lapping. Dipterans undergo complete metamorphosis. Flies and mosquitoes are among the best-known dipterans,
which live as scavengers, predators, and parasites.
Hemipterans are so-called “true bugs,” including bed bugs,
assassin bugs, and chinch bugs. (Insects in other orders are
sometimes erroneously called bugs.) Hemipterans have two
pairs of wings, one pair partly leathery, the other membranous.
They have piercing or sucking mouthparts and undergo
incomplete metamorphosis.
Ants, bees, and wasps are generally highly social insects. They
have two pairs of membranous wings, a mobile head, and
chewing or sucking mouthparts. The females of many species
have a posterior stinging organ. Hymenopterans undergo complete metamorphosis.
Termites are widespread social insects that produce enormous
colonies. It has been estimated that there are 700 kg of
termites for every person on Earth! Some termites have two
pairs of membranous wings, while others are wingless. They
feed on wood with the aid of microbial symbionts carried in
specialized chambers in their hindgut.
Figure 33.37
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Earwig
Horsefly
LeafFooted
bug
Cicada-killer wasp
Termite
• Insects are classified into about 26 orders
ORDER
Lepidoptera
Odonata
APPROXIMATE
NUMBER OF
SPECIES
120,000
5,000
EXAMPLE
MAIN CHARACTERISTICS
Butterflies and moths are among the best-known insects. They
have two pairs of wings covered with tiny scales. To feed, they
uncoil a long proboscis. Most feed on nectar, but some species
feed on other substances, including animal blood or tears.
Swallowtail
butterfly
Dragonflies and damselflies have two pairs of large, membranous wings. They have an elongated abdomen, large, compound
eyes, and chewing mouthparts. They undergo incomplete metamorphosis and are active predators.
Dragonfly
Orthoptera
13,000
Grasshoppers, crickets, and their relatives are mostly herbivorous. They have large hind legs adapted for jumping, two
pairs of wings (one leathery, one membranous), and biting or
chewing mouthparts. Males commonly make courtship sounds
by rubbing together body parts, such as a ridge on their hind
leg. Orthopterans undergo incomplete metamorphosis.
Katydid
Phasmida
Phthiraptera
Siphonaptera
Thysanura
2,600
2,400
2,400
450
Stick insects and leaf insects are exquisite mimics of plants. The
eggs of some species even mimic seeds of the plants on which the
Insects live. Their body is cylindrical or flattened dorsoventrally.
They lack forewings but have fanlike hind wings. Their
mouthparts are adapted for biting or chewing.
Commonly called sucking lice, these insects spend their entire
life as an ectoparasite feeding on the hair or feathers of a single
host. Their legs, equipped with clawlike tarsi, are adapted for
clinging to their hosts. They lack wings and have reduced eyes.
Sucking lice undergo incomplete metamorphosis.
Fleas are bloodsucking ectoparasites on birds and mammals.
Their body is wingless and laterally compressed. Their legs are
modified for clinging to their hosts and for long-distance
jumping. They undergo complete metamorphosis.
Stick insect
Human
Body
louse
Flea
Silverfish are small, wingless insects with a flattened body and
reduced eyes. They live in leaf litter or under bark. They can also
infest buildings, where they can become pests.
Silverfish
Trichoptera
7,100
Figure 33.37
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The larvae of caddisflies live in streams, where they make houses
from sand grains, wood fragments, or other material held together by silk. Adults have two pairs of hairy wings and chewing
or lapping mouthparts. They undergo complete metamorphosis.
Caddisfly
Crustaceans
• While arachnids and insects thrive on land
– Crustaceans, for the most part, have remained
in marine and freshwater environments
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• Crustaceans, subphylum Crustacea
– Typically have biramous, branched,
appendages that are extensively specialized
for feeding and locomotion
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• Decapods are all relatively large crustaceans
– And include lobsters, crabs, crayfish, and
shrimp
(a) Ghost crabs (genus Ocypode) live on sandy ocean
beaches worldwide. Primarily nocturnal, they take
Figure 33.38a
shelter in burrows during the day.
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• Planktonic crustaceans include many species
of copepods
– Which are among the most numerous of all
animals
Figure 33.38b
(b) Planktonic crustaceans
known as krill are
consumed in vast
quantities by whales.
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• Barnacles are a group of mostly sessile
crustaceans
– Whose cuticle is hardened into a shell
Figure 33.38c
(c) The jointed appendages
projecting from the shells
of these barnacles capture
organisms and organic
particles suspended in
the water.
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• Concept 33.8: Echinoderms and chordates are
deuterostomes
• At first glance, sea stars and other
echinoderms, phylum Echinodermata
– May seem to have little in common with
phylum Chordata, which includes the
vertebrates
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• Chordates and echinoderms share
characteristics of deuterostomes
– Radial cleavage
– Development of the coelom from the
archenteron
– Formation of the mouth at the end of the
embryo opposite the blastopore
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Echinoderms
• Sea stars and most other echinoderms
– Are slow-moving or sessile marine animals
• A thin, bumpy or spiny skin
– Covers an endoskeleton of hard calcareous
plates
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• Unique to echinoderms is a water vascular
system
– A network of hydraulic canals branching into
tube feet that function in locomotion, feeding,
and gas exchange
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.
Digestive glands secrete
digestive juices and aid in
the absorption and storage
of nutrients.
Figure 33.39
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.
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Stomach
Anus
Spine
Gills
Ring
canal
Gonads
Radial
nerve
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.
Madreporite. Water can flow
in or out of the water vascular
system into the surrounding
water through the madreporite.
Ampulla
Podium
Tube
feet
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.
• The radial anatomy of many echinoderms
– Evolved secondarily from the bilateral
symmetry of ancestors
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• Living echinoderms are divided into six classes
Table 33.6
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Sea Stars
• Sea stars, class Asteroidea
– Have multiple arms radiating from a central
disk
• The undersurfaces of the arms
– Bear tube feet, each of which can act like a
suction disk
Figure 33.40a
(a) A sea star (class Asteroidea)
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Brittle Stars
• Brittle stars have a distinct central disk
– And long, flexible arms
Figure 33.40b (b) A brittle star (class Ophiuroidea)
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Sea Urchins and Sand Dollars
• Sea urchins and sand dollars have no arms
– But they do have five rows of tube feet that
function in movement
Figure 33.40c (c) A sea urchin (class Echinoidea)
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Sea Lilies and Feather Stars
• Sea lilies
– Live attached to the substrate by a stalk
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Sea Cucumbers
• Feather stars
– Crawl about using their long, flexible arms
Figure 33.40d
(d) A feather star (class Crinoidea)
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Sea Cucumbers
• Sea cucumbers
– Upon first inspection do not look much like
other echinoderms
– Lack spines, and their endoskeleton is much
reduced
Figure 33.40e
(e) A sea cucumber (class Holothuroidea)
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Sea Daisies
• Sea daisies were discovered in 1986
– And only two species are known
Figure 33.40f
(f) A sea daisy (class Concentricycloidea)
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Chordates
• Chordates
– Phylum Chordata
– Consists of two subphyla of invertebrates as
well as the hagfishes and the vertebrates
– Shares many features of embryonic
development with echinoderms
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• A summary of animal phyla
Table 33.7
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