Download Ch 26 Arthropod Notes

Chapter 30
Arthropods
I. Features of Arthropods
• A typical arthropod is a segmented,
coelomate invertebrate animal with
bilateral symmetry, an exoskeleton, and
jointed structures called appendages.
• A. Jointed appendages:
“joint foot”=arthropoda
• An appendage is any
structure, such as a leg ,
an antenna, or
mouthpart that grows
out of the body of an
animal.
What is an arthropod?
• Joints also allow
powerful
movements of
appendages,
and enable an
appendage to
be used in many
different ways.
• Mouthparts
have sucking,
ripping or
chewing parts
Origins of Arthropods
Origins of Arthropods
• Arthropods most likely evolved from an ancestor
of the annelids.
• Oldest, best –preserved
multicellular animal fossils
• 600 million years old
• Most numerous early arthropod: trilobites
• -became extinct about 250 million years ago
• Lived in the sea
• Segmented bodies
• Jointed appendages
• First animals with eyes capable of forming images.
• First terrestrial arthropods: scorpions
The total number of arthropods
• Exceeds that of all other kinds of animals
combined .
• 5,000,000 species
• More species of beetles than vertebrates.
• Size varies from 80 micrometers (parasitic mite)to 3.6 m (giant crab found in the sea near
Japan.)
Two main groups
•Arthropods with jaws
1.-Uniramia – (subphylum) insects
chilopoda and diplopoda
2. Crustacea- (subphylum) shrimp, crab
lobster
•Arthropods with fangs and pincers
1. Chelicerata (subphylum) – scorpions, mites,
spiders
***Each subphyla represents a distinct
evolutionary line.
Arthropod Body Plan
Segmentation in arthropods
• In most groups of arthropods, segments have
become fused into three body sections—head,
thorax (mid body region), and abdomen.
• Individual body segments often exist only in
larval stages. (ex: catepillar)
Segmentation in arthropods
• In other groups,
even these
segments may
be fused.
• Some arthropods
have a head and
a fused thorax
and abdomen.
Segmentation in arthropods
• In other groups, there is an abdomen and a
fused head and thorax called a
cephalothorax.
• Fusion of the body segments is related to
movement and protection.
Arthropods have acute senses
• A compound eye is a visual structure with many
lenses.
• See motion much
more quickly than
humans.
• Accurate vision is also important to the active
lives of arthropods.
• Most arthropods have one pair of large
compound eyes and three to eight simple
eyes.
• A simple eye is a visual structure with only
one lens that is used for detecting light.
• In dragonflies and locusts, these simple eyes
function as horizon detectors. –helps them
stabilize their position in flight.
Arthropod exoskeletons provide
protection
• The exoskeleton is a hard, thick, outer
covering made of protein and chitin (KI tun).
• Brittle and can break easily
Arthropod exoskeletons provide
protection
• In some species, the exoskeleton is a
continuous covering over most of the body.
• In other species, the exoskeleton is made of
separate plates held together by hinges.
• Crustaceans : thick relatively inflexible
exoskeleton.
• Insects and arachnids: soft and flexible
exoskeleton.
Arthropod exoskeletons provide
protection
• The exoskeleton protects and supports
internal tissues and provides places for
attachment of muscles.
• In many aquatic species, the exoskeletons are
reinforced with calcium carbonate.
Why arthropods must molt
• Exoskeletons have their disadvantages.
• First, they are relatively heavy structures.
The larger an arthropod is, the thicker and
heavier its exoskeleton must be to support its
larger muscles.
Why arthropods must molt
• A second and more important disadvantage is
that exoskeletons cannot grow, so they must
be shed periodically. Shedding the old
exoskeleton is called molting.
Why arthropods must molt
• When the new exoskeleton is ready, the
animal contracts muscles and takes in air or
water.
• This causes the animal’s body to swell until
the old exoskeleton splits open, usually
along the back.
Why arthropods must molt
• Before the new exoskeleton hardens, the
animal puffs up as a result of increased blood
circulation to all parts of its body.
• Thus, the new exoskeleton hardens in a
larger size, allowing some room for the
animal to continue to grow.
Why arthropods must molt
• Most arthropods molt four to seven times in their
lives before they become adults.
• When the new exoskeleton is soft, arthropods
cannot protect themselves from danger
because they move by bracing muscles
against the rigid exoskeleton.
Respiration: Arthropods have efficient
gas exchange
• Arthropods have efficient respiratory
structures that ensure rapid oxygen
delivery to cells.
• This large oxygen demand is needed to
sustain the high levels of metabolism
required for rapid movements.
Arthropods have efficient gas exchange
• Three types of
respiratory
structures
have evolved
in arthropods:
gills, tracheal
tubes, and
book lungs.
Arthropods have efficient gas exchange
• Aquatic
arthropods
exchange gases
through gills,
which extract
oxygen from
water and
release carbon
dioxide into the
water.
Arthropods have efficient gas exchange
• Land arthropods have either a system of tracheal
tubes or book lungs.
Arthropods have efficient gas exchange
• Most insects have tracheal tubes, branching
networks of hollow air passages that carry air
throughout the body.
Arthropods have efficient gas exchange
• Muscle activity helps pump the air through
the tracheal tubes.
• Air enters and leaves the tracheal tubes
through openings on the thorax and
abdomen called spiracles.
Arthropods have efficient gas exchange
• Most spiders and their relatives have book lungs,
air-filled chambers that contain leaflike plates.
Arthropods have efficient gas exchange
• The stacked plates of a book lung are arranged
like pages of a book.
Excretion:
• Most terrestrial arthropods excrete wastes
through Malpighian tubules.
• Slender, fingerlike extensions from the
arthropods gut that are bathed in blood.
• In insects, the tubules are all located in the
abdomen rather than in each segment.
• Malpighian tubules are attached to and empty
into the intestine.
• Metabolic wastes remain in the gut and leave
the body through the anus.
II. Spiders and other Arachnids
What is an arachnid?
• Spiders, scorpions, mites, and ticks belong to the
class Arachnida (uh RAK nud uh).
• Spiders are the largest group of arachnids.
• Spiders and other arachnids have only two body
regions—the cephalothorax and the abdomen.
• They have no antennae
• Arachnids have six pairs of jointed appendages.
What is an arachnid?
• The first pair of appendages, called
chelicerae, is located near the mouth.
chelicerae
What is an arachnid?
• Chelicerae are often modified into pincers or
fangs.
• Pincers are used to hold food, and fangs
inject prey with poison.
What is an arachnid?
• Spiders have no mandibles for chewing.
• Using a process of extracellular digestion,
digestive enzymes from the spider’s mouth
liquefy the internal organs of the captured prey.
The spider then sucks up the liquefied food.
What is an arachnid?
• The second pair of appendages, called the
pedipalps, are adapted for handling food and for
sensing.
pedipalps
• Sometimes the pedipelps are for reproduction.
• Following the pedipalps, are 4 pairs of
appendages called walking legs.
What is an arachnid?
• Although all spiders spin silk, not all make webs.
• Spider silk is secreted by silk glands in the
abdomen.
What is an arachnid?
• As silk is
secreted, it is
spun into thread
by structures
called spinnerets,
located at the
rear of the spider.
A Spider
Legs
Simple eyes
Cocoon
Pedipalps
Book Lungs
Silk glands
Chelicerae
• Spiders are predatory animals, feeding
almost exclusively on other
arthropods.(=carnivores)
Ticks, mites, and scorpions: Spider
relatives
• Ticks and mites differ from spiders in that
they have only one body section.
tick
Ticks, mites, and scorpions: Spider
relatives
• The head, thorax, and abdomen are
completely fused.
• Plant mites- while feeding may pass viral
and fungal infections to plants.
• Dust mites- live in carpet, bedding, clothing.
(cause allergies)
• Chiggers-known for their irritating bite
• Ticks feed on blood from reptiles, birds,
and mammals.
Ticks, mites, and scorpions: Spider
relatives
• Mites feed on fungi, plants, and animals.
• They are so small that they often are not visible
to the unaided human eye.
• Like ticks, mites can transmit diseases.
• Lyme disease is spread by deer ticks
Ticks, mites, and scorpions: Spider
relatives
• Scorpions are easily
recognized by their
many abdominal body
segments and enlarged
pincers.(=pedipalps)
• They have a long tail with
a venomous stinger at
the tip. Which is used to
stun their prey.
Insects
• Flies, grasshoppers, lice, butterflies, bees, and
beetles are just a few members of the class
Insecta.
• Insects have three body segments (head thorax
and abdomen) and six legs.
• Head- mandibles (chewing mouth part)
pair of antennae, compound eyes
• Thorax - (composed of 3 fused segments.)
• 3 pair of jointed walking legs and some have
wings that are attached to the thorax.
• Abdomen- is composed of 9-11 segments
Arthropods have other complex body
systems
• The mandibles, together with other mouthparts
are adapted for holding, chewing, sucking, or
biting the various foods eaten by arthropods.
A Grasshopper
Antennae
Legs
Eyes
Wings
Spiracles
Malpighian tubules
Tympanum
Nervous System
Insect reproduction/Life Cycle
• Insects usually mate once during their
lifetime.
• The eggs usually are fertilized internally.
• Some insects exhibit parthenogenesis,
reproducing from unfertilized eggs.
Insect reproduction
• Most insects lay a
large number of
eggs, which increase
the chances that
some offspring will
survive long enough
to reproduce.
Metamorphosis: Change in body shape
and form
• After eggs are laid, the insect embryo develops
and the eggs hatch.
• In some wingless insects development is direct;
the eggs hatch into miniature forms that look
just like tiny adults.
Metamorphosis: Change in body shape
and form
Nymph
Molt
Eggs
Nymph
Molt
Adult
• These insects
go through
successive
molts until the
adult size is
reached.
Metamorphosis: Change in body shape
and form
• In some cases,
the adult insect
bears little
resemblance to
its juvenile
stage.
Adult
Egg
Pupa
Larva
Metamorphosis: Change in body shape
and form
• This series of changes, controlled by
chemical-substances in the animal, is
called metamorphosis.
• Insects that undergo metamorphosis usually
go through four stages on their way to
adulthood: egg, larva, pupa, and adult.
Metamorphosis: Change in body shape
and form
• The larva is the free-living, wormlike stage of an
insect, often called a caterpillar.
Metamorphosis: Change in body shape
and form
• The pupa stage of insects is a period of
reorganization in which the tissues and organs of
the larva are broken down and replaced by adult
tissues.
• Usually the insect does not move or feed
during the pupa stage. After a period of
time, a fully formed adult emerges from the
pupa.
Metamorphosis: Change in body shape
and form
• The series of changes that occur as an insect
goes through the egg, larva, pupa, and adult
stages is known as complete metamorphosis.
• Complete metamorphosis is an advantage
for arthropods because larvae do not
compete with adults for the same food.
Metamorphosis:
Change in body
shape and form
larvae
fertilized egg
• The complete
metamorphosis
of a butterfly is
illustrated.
adult
pupa
Metamorphosis: Change in body shape
and form
• Other insects that undergo complete
metamorphosis include ants, beetles, flies,
and wasps.
Incomplete metamorphosis has three
stages
• Many insect species, as well as other
arthropods, undergo a gradual or incomplete
metamorphosis, in which the insect goes through
only three stages of development.
• These three stages are egg, nymph, and adult.
Incomplete metamorphosis has three
stages
Nymph
Molt
Eggs
Nymph
Molt
Adult
• A nymph, which
hatches from an
egg, has the
same general
appearance as
the adult but is
smaller and
wingless.
Incomplete metamorphosis has three
stages
• Nymphs cannot reproduce.
• As the nymph eats and grows, it molts several
times. With each molt, it begins to resemble the
adult more.
• Gradually, the nymph becomes an adult.
Incomplete metamorphosis has three
stages
• Grasshoppers and cockroaches are insects that
undergo incomplete metamorphosis.
Incomplete metamorphosis of a harlequin bug
Social Insects
• Two orders of insects, Hymenoptera (bees)
and Isoptera (termites) have elaborate social
systems.
• They have division of labor. Each having their
own job. (worker, drone, soldier, queen ,king)
• The role played by the individual in a colony is
called its caste.
• Its Caste is determined by a combination of
heredity, diet, hormones and pheromones
Insect relatives
Centipedes and Millipedes
• Like spiders, millipedes and centipedes have
Malpighian tubules for excreting wastes.
• In contrast to spiders, centipedes and millipedes
have tracheal tubes rather than book lungs for
gas exchange.
Centipedes and Millipedes
• Centipedes are carnivorous and eat soil
arthropods, snails, slugs, and worms.
• Centipedes have one pair of legs /segment
• The bites of some centipedes are painful
to humans.
Centipedes and Millipedes
• A millipede eats mostly plants and dead material
on damp forest floors. (herbivores)
• Millipedes do not bite, but they can spray
foul-smelling fluids from their defensive stink
glands.
• Millipedes have 2 pair of legs /segment
Crustaceans
• Members of the class Crustacea include crabs,
lobsters, shrimps, crayfishes, water fleas, pill bugs,
and barnacles.
• Barnacles are sessile
• Many have a distinctive
larval form called a
nauplius .
• The nauplius has 3 pair
of branched appendages
and undergoes a series
of molts.(pg 680)
Crustaceans
• Sow bugs and pill bugs, two of the few
terrestrial crustaceans, must live where
there is moisture, which aids in gas
exchange.
• Most crustaceans are aquatic and exchange
gases as water flows over feathery gills.
• Shrimp, water fleas, ostracods ,copepods
• Copepods are among the most abundant
multi-cellular organism on earth and along with
krill they are a major food source in the
oceans.
Decapods
• Crustaceans (krus TAY
shuns) this type have two
pairs of antennae for
sensing.
• 5 pairs of legs
• Anterior pair of legs are
modified into large pincers
• Swimmerets- are
called chelipeds.
appendages attached
• Cephalathorax (called a
to the underside for
carapace)
swimming and
reproduction
• Uropods-flattened, paddle
like appendages
• Telson- tail spine
Crustaceans
claw
legs
• The first pair of walking legs are often modified
into strong claws for defense. (Cheliped)