Arthropods and Echinoderms
Chapter 28
ARTHROPODS
“arthro” means joint
“pod” means foot
28-1 Introduction to Arthropods
What Is An Arthropod?
• Phylum Arthropoda
• Coelomate
• Bilateral Symmetry
• Tough exoskeleton
made of chitin
• Segmented body
• Jointed appendages
(growing out of body)
•crabs, crayfish, centipedes
insects,, spiders, scorpions
28-1 Introduction to Arthropods
What Is An Arthropod?
Exoskeletons
• made of protein and CHITIN (carbohydrate)
• May be a continuous
covering most of body
• May be made of plates
held together by hinges
28-1 Introduction to Arthropods
What Is An Arthropod?
Exoskeleton Advantages
• Protects, supports internal tissues
• Provides place for muscle attachment
• Aquatic arthropods have exoskeleton reinforced
with calcium carbonate
28-1 Introduction to Arthropods
What Is An Arthropod?
Exoskeleton Disadvantages
• Heavy
the larger the animal, the thicker and
heavier the exoskeleton
• Exoskeletons don’t grow
animals must molt when they get too
large for exoskeleton
28-1 Introduction to Arthropods
What Is An Arthropod?
Appendages
Appendages
Jointed Appendages
28-1 Introduction to Arthropods
What Is An Arthropod?
Segmentation
3 Segments
abdomen
thorax
head
28-1 Introduction to Arthropods
What Is An Arthropod?
Segmentation
No Segmentation
Segmentation
28-1 Introduction to Arthropods
What Is An Arthropod?
Segmentation
• Sometimes segments
are fused together
• some have abdomen
and fused head/thorax
(cephalothorax)
28-1 Introduction to Arthropods
Question 1
Which of the following organisms would be
most likely to have an exoskeleton reinforced
with calcium carbonate?
Spider
Beetle
Crab
Dragonfly
Crab
28-1 Introduction to Arthropods
Question 2
Exoskeletons are heavy. Why can aquatic
arthropods grow larger than terrestrial arthropods?
The buoyancy of the water helps support the
weight of the exoskeleton.
28-1 Introduction to Arthropods
Question 3
What is one advantage and one disadvantage of
flying arthropods having a thinner, lighter
weight exoskeleton?
Disadvantage: less protection, more fragile
Advantage: greater freedom to fly and jump
28-1 Introduction to Arthropods
Question 4
What is one advantage and one disadvantage of
having a cephalothorax?
Disadvantage: less flexibility, mobility
Advantage: more protection
28-1 Introduction to Arthropods
Evolution of Arthropods
28-1 Introduction to Arthropods
Arthropod Feeding
• Herbivores, carnivores,
omnivores, bloodsuckers,
filter feeders, detritivores,
and parasites
• Mouthparts have evolved
to allow them to eat
anything imaginable
• Pincers or fangs to sickleshaped jaws that can cut
through the tissues of
captured prey
28-1 Introduction to Arthropods
Respiration: Terrestrial Arthropods
Tracheal tubes
branching network of hollow air passages that
take air throughout the body
Muscle
movement
brings air in/out
through
SPIRACLES
(openings in
abdomen and
thorax)
28-1 Introduction to Arthropods
Respiration: Terrestrial Arthropods
Book lungs
spiders and relatives
air filled chambers with leaf-like plates
stacked plates
are arranged
like pages
of a book
28-1 Introduction to Arthropods
Respiration: Aquatic Arthropods
Gills
water moves over gills
O2 from water diffuses
into gills and into
bloodstream
CO2 from body diffuses out through gills into
surrounding water
28-1 Introduction to Arthropods
Respiration: Aquatic Arthropods
• Respire through
feather-like gills
(lobster and
crabs)
• The horseshoe
crab respires
through organs:
book gills
28-1 Introduction to Arthropods
Arthropod Circulatory System
• Open circulatory system
• Well-developed heart pumps blood through arteries that branch
and enter the tissues
• Blood leaves the blood vessels and moves through sinuses, or
cavities
• The blood recollects in a large sinus surrounding the heart
• It reenters the heart and is again pumped throughout the body
28-1 Introduction to Arthropods
Arthropod Circulatory System
28-1 Introduction to Arthropods
Arthropod Excretion
Terrestrial Arthropods
•Malpighian tubules:
sac-like organ that extracts
wastes from the blood and
adds them to feces that
move through the gut
Aquatic Arthropods
• Diffusion moves cellular wastes from the
arthropod’s body into the surrounding water
28-1 Introduction to Arthropods
Arthropod Nervous System
• Anterior brain
• Double ventral
nerve cord
• Several fused
ganglia that control
the body section
they are located in
28-1 Introduction to Arthropods
Arthropod Digestive System
Complete digestive system with mouth,
intestine, and anus
Mouth has 1 pair of jaws called
MANDIBLES
adapted for holding, chewing, sucking, or biting
28-1 Introduction to Arthropods
Arthropod Response
• Well-developed nervous system
• Brain
• Sophisticated sense organs:
eyes, taste receptors
28-1 Introduction to Arthropods
Arthropod Eyes
Compound Eyes
visual structure with
many lenses
Simple Eyes
visual structure with one lens for detecting light
one pair of compound eyes and 3-8 simple eyes
28-1 Introduction to Arthropods
Arthropod Antennae
Acute sensing by antennae
Stalk like structure, detects
changes environment
movement
sound
chemicals
used for sound and odor
communication
28-1 Introduction to Arthropods
Arthropod Movement
• Well-developed groups of muscles
that are coordinated and controlled
by the nervous system
Allows arthropods to
• beat their wings to fly in air
• push their legs to walk on ground
• beat their flippers to swim in water
28-1 Introduction to Arthropods
Reproduction: Sexual
Female or Male (not hermaphroditic)
Terrestrial Arthropods
• Internal fertilization
• Sperm or sperm packet
Aquatic Arthropods
• Internal or external
fertilization
28-1 Introduction to Arthropods
Reproduction: Asexual
Parthenogenesis
“parthenos” means virgin and “genesis” means birth
• new individuals develop from unfertilized eggs
• seen in ants, aphids and bees
28-1 Introduction to Arthropods
Growth and Development in Arthropods
Molting
• skin glands digest inner part of exoskeleton and other glands
secrete a new skeleton
• Animal contracts muscles and takes in air or water, body
swells, exoskeleton splits, usually along back
• The animal pulls itself out of the remains of the original
skeleton…this can take several hours
• The new exoskeleton is soft and the animal is vulnerable to
predators
•
Most arthropods molt 4-7 times before becoming an adult.
28-1 Introduction to Arthropods
Growth and Development in Arthropods
Molting
28-2 Groups of Arthropods
• Classified based on the number and structure
of their body segments and appendagesparticularly their mouthparts
– Crustaceans
– Spiders and their relatives
– Insects and their relatives
28-2 Groups of Arthropods
Crustaceans
• 2 pairs of branched antennae
• 5 pairs of legs
• 2-3 body sections
• Mandibles: mouthparts
• Compound eyes
• Primarily aquatic
• Examples: crabs, shrimps, lobsters, crayfish, barnacles
28-2 Groups of Arthropods
Crustaceans
• 5 pairs of walking legs
• 1st pair are claws for defense
claw
legs
28-2 Groups of Arthropods
Crustaceans
• Cephalothorax: region of a
crustacean formed by the
fusion of the head with the
thorax
• Thorax: body part of
crustacean that lies just
behind the head and houses
most of the internal organs
• Abdomen: posterior part of
an arthropod’s body
28-2 Groups of Arthropods
Crustaceans
• Carapace: the part of the
exoskeleton that covers the
cephalothorax
• Mandible: mouthpart adapted
for biting and grinding food
• Cheliped: one of the first pair
of legs of decapods (five pairs
of legs: crayfishes, lobsters and
crabs)
• Swimmerets: flipper-like
appendages used by decapods
for swimming
28-2 Groups of Arthropods
Crustaceans
• Most are aquatic and use gills
• pill bugs (rollie-pollie) live on land, but must
have moisture to aid in gas exchange
This is a
terrestrial
crustacean!
28-2 Groups of Arthropods
Spiders and Their Relatives
• subphylum Chelicerata
• Mouthparts: chelicerae
and pepipalps
• 2 body sections
• 4 pairs of walking legs
• Horseshoe crabs, spiders,
ticks, and scorpions
28-2 Groups of Arthropods
Spiders and Their Relatives
28-2 Groups of Arthropods
Horseshoe Crabs
• Class Merostomata
“Living Fossils”- unchanged for 220 million
years (Triassic period)
• Extensive exoskeleton
• Live in deep coastal waters
• forage bottoms for algae,
annelids and mollusks
• Chelicerae, five pairs of walking legs, a long
spike-like tail used for movement
28-2 Groups of Arthropods
Arachnids: Spiders
• The largest group
of arachnids
• Spin webs of a
strong, flexible
protein called silk
• Do not have jaws
for chewing: must
liquefy food to
swallow it
28-2 Groups of Arthropods
Arachnids: Spiders
• Chelicerae: pair of mouthparts
in chelicerates that contain
fangs and are used to stab and
paralyze prey
• Pedipalps: pair of mouthparts
in chelicerates that are usually
modified to grab prey
• Spinneret: organ in spiders
that contains silk glands
28-2 Groups of Arthropods
Arachnids: Spiders
• spiders (largest group), ticks, mites, scorpions
• 2 body regions: cephalothorax and abdomen
• 6 pairs of jointed appendages -12 total appendages
28-2 Groups of Arthropods
Arachnids: Spiders
1st pair - chelicerae, are near the mouth
chelicerae
modified into pincers (hold food) or fangs (inject poison)
28-2 Groups of Arthropods
Arachnids: Spiders
2nd pair - pedipalps, handling food
pedipalps
Also used for sensing
28-2 Groups of Arthropods
Arachnids: Spiders
• silk is secreted by silk glands in the abdomen
• as it is secreted, it is spun into thread by
SPINNERETTES
• spiders are predatory and feed almost
exclusively on other animals
28-2 Groups of Arthropods
Arachnids: Mites and Ticks
• Ticks and mites have only 1 body section
Tick
Eyelash Mite
• Head, thorax and abdomen are completely fused
• Ticks feed on blood of other animals
28-2 Groups of Arthropods
Arachnids: Mites and Ticks
• Small arachnids that are usually parasitic
• Chelicerae and pedipalps are
specialized for digging into a
host’s tissues and sucking out
blood or plant fluids
Tick
• Mouthparts are so strong that if you try to pull off a
tick the cephalothorax may separate from the
abdomen and remain in your skin
28-2 Groups of Arthropods
Arachnids: Mites and Ticks
• Mites feed on fungi, plants, and animals
• small – not usually visible
• can transmit diseases
Dust Mites
Skin Mites
28-2 Groups of Arthropods
Arachnids: Scorpions
• Widespread in warm areas around the world
• Have pedipalps that are
enlarged into claws
• The long, segmented
abdomen of a scorpion
carries a venomous
stinger that can kill
or paralyze prey
• Chew their prey using their chelicerae
28-2 Groups of Arthropods
Arachnids: Scorpions
• Scorpions have many abdominal body segments
• Enlarged pincers
• Long tail with
venomous stinger
at the tip
28-2 Groups of Arthropods
Insects and Their Relatives
• Uniramians have jaws, one pair of antennae,
and unbranched appendages
• A group that contains more species than any
other group of animals living today
• Wide variety of
forms and lifestyles
– Centipedes
– Millipedes
28-2 Groups of Arthropods
Insects
• 3 body segments
• 6 legs
• Very diverse - more
insects than all
other classes of
animals combined
• Flies, grasshoppers,
lice, butterflies,
beetles
28-2 Groups of Arthropods
Centipedes and Millipedes
Centipedes are carnivorous, predators – eat soil
arthropods, snails, slugs, worms
• Bites can be painful
• 1 pair of legs/segment
• Class Chilopoda
• Millipedes are timid plant eaters and feed on dead
material on damp forest floors
• Do not bite, spray stinky fluid
• 2 pairs of legs/segment
• Class Diplopoda
28-2 Groups of Arthropods
Question 5
Spiders are:
predators
scavengers
decomposers
parasites
Predators!
28-2 Groups of Arthropods
Question 6
Having 2 pairs of antennae distinguish
_________ from other arthropods.
centipedes
millipedes
crustaceans
horseshoe crabs
Crustaceans
28-2 Groups of Arthropods
Question 7
Why are horseshoe crabs called “living fossils?”
They have
remain
unchanged
after 220
million
years!
28-3 Insects
• body divided into 3 parts:
– Head
– Thorax
– Abdomen
• three pairs of legs are
attached to the thorax
• like all arthropods, insects
have a segmented body,
exoskeleton, and jointed
appendages
28-3 Insects
28-3 Insects
Insect Responses to Stimuli
• Multiple of sense organs are
used to respond to stimuli
• Compound eyes
• Chemical receptors for
taste and smell on their
mouthparts
• Well-developed ears that hear
sounds far above the human
range
28-3 Insects
Insect Adaptations for Feeding
• Three pairs of appendages that are used as mouthparts,
including a pair of mandibles
• Adaptations for feeding not restricted to mouthparts
• Many produce saliva containing digestive enzymes that help
break down food
28-3 Insects
Insect Movement and Flight
• 3 pairs of legs
• Used for walking, jumping,
flying, capturing and holding
prey
• The evolution of flight has
allowed insects to disperse
long distances and to colonize
a wide variety of habitats
28-3 Insects
Insect Reproduction
• mate once in lifetime
• internal fertilization
• some exhibit
parthenogenesis
“virgin” “birth”
• large number of eggs
to increase survival rate
28-3 Insects
Insect Metamorphosis
• insect embryos
develop in eggs
Eggs
Nymph
Molt
Nymph
Adult
Molt
• eggs hatch
• some look like
miniature adults
• will molt several
times until adult
size
28-3 Insects
Insect Metamorphosis
• Incomplete metamorphosis:
type of insect development
characterized by a similar
appearance throughout all
stages of the life cycle
• Nymph: immature form that
lacks functional sex organs
and other adult structures
28-3 Insects
Insect Metamorphosis
INCOMPLETE METAMORPHOSIS
• 3 stages:
Nymph
Molt
egg, nymph, adult
Eggs
Nymph
•Nymphs can not
reproduce
Molt
Adult
• Nymph gradually
becomes an adult
28-3 Insects
Insect Metamorphosis
• Complete metamorphosis: type of insect development
in which the larvae look and act nothing like their
parents and also feed in completely different ways
• Pupa: stage of
metamorphosis in
which an insect
changes from a
larva into an adult
28-3 Insects
Insect Metamorphism
COMPLETE METAMORPHOSIS
• 4 stages:
Adult
Egg
egg, larva, pupa, adult
• metamorphosis is
controlled by chemical
substances in the insect
Larva
Pupa
28-3 Insects
Insect Metamorphosis
• Incomplete metamorphosis:
grasshoppers
cockroaches
•Complete metamorphosis:
ants
beetles
flies
wasps
28-3 Insects
Insects and Humans
• Many insects are known for their negative effects
• Termites destroy wood structures, moths eat their way
through wool clothing, etc.
• Despite their association with destruction and disease,
insects contribute to agriculture by pollinating 1/3 of
the food that you eat
• Produce commercially valuable silk, wax and honey
28-3 Insects
Insect Communication
• Communicate using sound, visual,
chemical, and other types of
signals
• Much of the communication
involves finding a mate
• Pheromones: specific chemical
messengers that affect the
behavior of development of other
individuals of the same species
28-3 Insects
Insect Societies
• Ants, bees, termites, and some of their relatives form
complex associations called societies
• Society: a group of closely related animals of the
same species that work together for the benefit of the
whole group
• Caste: group of individual insects specialized to
perform particular tasks, or roles
ECHINODERMS
“ichino” means spiny
“derm” means skin
28-4 Echinoderms
28-4 Echinoderms
What is an Echinoderm?
• Phylum Echinodermata
• Live only in the sea
• Spiny skin
• Water vascular system
• Tube feet: suctioncuplike structures
• Five-part radial symmetry
•Endoskeleton: internal skeleton; hardened calcium carbonate
28-4 Echinoderms
Form and Function in Echinoderms
• The water vascular system, which is filled with
fluid, carries out many essential body functions in
echinoderms including respiration, circulation, and
movement
• Madreporite: sieve-like structure
through which the water vascular
system of an echinoderm opens to
the outside near the anus.
28-4 Echinoderms
Echinoderm Feeding
• Several methods of feeding
• Sea urchins use five-part
jaw-like structures to scrape
algae from rocks
• Sea lilies use tube feet to
capture floating plankton
• Sea stars feed on mollusks by pushing the stomach
out through the mouth
28-4 Echinoderms
Echinoderm Respiration and
Circulation
• Other than the water vascular system,
echinoderms have few adaptations to carry out
respiration or circulation
• In most species, the
thin-walled tissue of
the tube feet provides
the main surface for
respiration
28-4 Echinoderms
Echinoderm Excretion
• Solid waste is released as feces through anus
• Nitrogen-containing cellular wastes are
excreted primarily in the form of ammonia
• It is passed through the tube feet and skin gills
28-4 Echinoderms
Echinoderm Response
• Do not have a highly developed nervous system
• Most have a nerve ring that surrounds the mouth and
radial nerves that connect the ring with the body
sections
• Most have scattered sensory cells that detect light,
gravity, and chemicals released by potential prey
28-4 Echinoderms
Echinoderm Movement
• Most move by tube
feet and thin layers
of muscle fibers
attached to their
endoskeleton
• Mobility is
determined by the
kind of endoskeleton
28-4 Echinoderms
Echinoderm Reproduction
• Reproduce by external fertilization
• The sexes are separate in most sea star species
28-4 Echinoderms
Groups of Echinoderms
• 7000 species
– Sea urchins and sand dollars
– Brittle stars
– Sea cucumbers
– Sea stars
– Sea lilies and feather stars
28-4 Echinoderms
Ecology of Echinoderms
• Common in a variety of marine habitats
• A rise or fall of echinoderms can cause major changes
to populations of other marine organisms
• Sea urchins control the distribution of algae and other
forms of marine life
• Sea stars are important carnivores that control the
numbers of other organisms such as clams and corals
Chapter 28 In A Nutshell
Arthropods
Echinoderms
•Crustaceans
•Starfish
•Spiders,
Scorpions,
Ticks, Mites
•Sea Urchins
•Millipedes
Centipedes
•Insects
• Sand Dollars
•Sea Lilies
•Sea Cucumbers
Arthropod Comparison
Crayfish
# of legs
10
Respiratory
organs
Gills
Excretory
organs
Green glands
Spiders
8
book lungs
Insects
6
Trachea/spiracles
OR
trachea/spiracles
Malpighian
tubules
Malpighian
tubules
Arthropod Comparison
Crayfish
Body
segments
Cephalothorax
Abdomen
Antenna?
2 pairs of
Antenna
Mouth parts
Mandible,
maxillae,
Maxillipeds
Eyes
Compound eyes
Spiders
Insects
Cephalothorax Head, thorax,
Abdomen
& abdomen
NO
antenna
1 pair of
antenna
chelicera,
pedipalps
mandible,
maxillae
labium, labrum
8 simple eyes
compound eyes
Animals in the Phylum Arthropoda
Animals in the Phylum Arthropoda
Subphylum Trilobitomorpha
Animals in the Phylum Arthropoda
Subphylum Trilobitomorpha
Subphylum Cheliceriformes
Class Chelicerata
Subclass Merostomata (horseshoe crabs)
Animals in the Phylum Arthropoda
Subphylum Trilobitomorpha
Subphylum Cheliceriformes
Class Chelicerata
Subclass Merostomata (horseshoe crabs)
Subclass Arachnida (spiders, scorpions, mites, ticks)
Animals in the Phylum Arthropoda
Subphylum Trilobitomorpha
Subphylum Cheliceriformes
Class Chelicerata
Subclass Merostomata (horseshoe crabs)
Subclass Arachnida (spiders, scorpions, mites, ticks)
Class Pycnogonida (sea spiders)
Animals in the Phylum Arthropoda
Subphylum Trilobitomorpha
Subphylum Cheliceriformes
Subphylum Myriapoda
Class Chilapoda (centipedes)
Animals in the Phylum Arthropoda
Subphylum Trilobitomorpha
Subphylum Cheliceriformes
Subphylum Myriapoda
Class Chilapoda (centipedes)
Class Diplopoda (millipedes)
Animals in the Phylum Arthropoda
Subphylum Trilobitomorpha
Subphylum Cheliceriformes
Subphylum Myriapoda
Subphylum Hexapoda
Class Insecta
Animals in the Phylum Arthropoda
Subphylum Trilobitomorpha
Subphylum Cheliceriformes
Subphylum Myriapoda
Subphylum Hexapoda
Subphylum Crustacea
Class Branchipoda (brine shrimp)
Animals in the Phylum Arthropoda
Subphylum Trilobitomorpha
Subphylum Cheliceriformes
Subphylum Myriapoda
Subphylum Hexapoda
Subphylum Crustacea
Class Branchipoda
Class Maxillopoda
Subclass Copepoda (copepod)
Animals in the Phylum Arthropoda
Subphylum Trilobitomorpha
Subphylum Cheliceriformes
Subphylum Myriapoda
Subphylum Hexapoda
Subphylum Crustacea
Class Branchipoda
Class Maxillopoda
Subclass Copepoda (copepod)
Subclass Thecostraca (barnacles)
Animals in the Phylum Arthropoda
Subphylum Trilobitomorpha
Subphylum Cheliceriformes
Subphylum Myriapoda
Subphylum Hexapoda
Subphylum Crustacea
Class Branchipoda
Class Maxillopoda
Class Malacostraca
Order Decapoda (crabs, lobsters, shrimp)
Animals in the Phylum Arthropoda
Subphylum Trilobitomorpha
Subphylum Cheliceriformes
Subphylum Myriapoda
Subphylum Hexapoda
Subphylum Crustacea
Class Branchipoda
Class Maxillopoda
Class Malacostraca
Order Decapoda
Order Isopoda (isopods)