Transcript Arthropods - walker2013

Arthropods
Chapter 28
Animal Classification
Invertebrates
Sponges
Cnidarians
Worms
Mollusks
Arthropods
Echinoderms
-Class Arachnida
-Class Crustacea
-Class Insecta
Animals
(cold-blooded)
Fishes
Amphibians
Reptiles
Endotherms
Birds
Mammals
Ectotherms
Vertebrates
(warm-blooded)
28-1: Characteristics of
Arthropods
Characteristics
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Arthropod comes from the Greek words
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“arthron” – joint
“pod” – foot
A typical arthropod is:
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Segmented
A coelomate
Has bilateral symmetry
Has an exoskeleton
Characteristics
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Appendages – any structure (a leg or an
antenna) that grows out of the body of an
animal
Characteristics
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Arthropods are the earliest known
invertebrates to exhibit jointed appendages
Joints are advantageous because they allow
more flexibility and powerful movements
Arthropod Exoskeletons Provide
Protection
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Exoskeleton is made of protein and
chitin (KI tun)
Chitin is also found in cell walls of fungi
The exoskeleton protects and supports
internal tissues and provides places for
attachment of muscles
Arthropod Exoskeletons Provide
Protection
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The weight of the exoskeleton limits the size
of arthropods
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The larger an arthropod is, the thicker and heavier
its exoskeleton must be to support its larger
muscles
Why Arthropods Must Molt
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Exoskeletons cannot
grow, so they must be
shed periodically
Molting – shedding the
old exoskeleton
Before an arthropod
molts, a new, soft
exoskeleton formed
beneath the old one
Cicada
Segmentation in Arthropods
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Arthropods do not have as many segments
as segmented worms
In most groups, arthropods are consisted of
three segments
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Head
Thorax
Abdomen
Segmentation in Arthropods
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Some arthropods have two sections
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Cephalothorax – A fused head and thorax
Abdomen
Arthropods Have Efficient Gas Exchange
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Three types of respiratory structures have
evolved in arthropods:
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1. Gills – Aquatic arthropods exchange oxygen
and carbon dioxide through gills
Arthropods Have Efficient Gas Exchange
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Land arthropods have either:
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2. Tracheal tubes – branching networks of hollow
air passages that carry air throughout the body
Arthropods Have Efficient Gas Exchange
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3. Book lungs – air-filled chambers that contain
leaf-like plates
Arthropods Have Acute Senses
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Movement, sound, and chemicals can be
detected with great sensitivity by antennae
Antennae are also used for sound and odor
communication; can detect pheromones
Atlas moth
Arthropods Have Acute Senses
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Pheromones – chemical odor signals given
off by animals
Some pheromones are used as scent trails
(example: the group-feeding behavior of ants)
Many pheromones are important in the
mating behavior of arthropods
Arthropods Have Acute Senses
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Most arthropods have one pair of large
compound eyes and three to eight simple
eyes
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A simple eye is a visual structure with only one
lens that is used for detecting light
Arthropods Have Acute Senses
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A compound eye is a visual structure with many
lenses
Compound eyes can detect the movements of
prey, mates, or predators, and can also detect
colors
Arthropods Have Acute Senses
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Arthropods have hairlike structures used to
detect movement
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Ex. Fly and flyswatter
Arthropod Nervous Systems are Well
Developed
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The nervous system consists of a double
ventral nerve cord, an anterior brain, and
several ganglia
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Ganglia act as control centers for the body
sections in which they are located
Arthropods Have Other Complex Body
Systems
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Arthropods have an open circulatory system
and a complete digestive system
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Mouth, stomach, intestine, and anus
Arthropods Have Other Complex Body
Systems
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Mandibles – the mouthparts of most
arthropod groups include one pair of jaws
The mandibles are adapted for holding,
chewing, sucking, or biting
Arthropods Have Other Complex Body
Systems
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Malpighian tubules –
used to excrete wastes
into the intestine
Arthropods Reproduce Sexually
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Some species (bees,
ants, and wasps)
exhibit parthenogenesis
– a form of asexual
reproduction in which a
new individual develops
from an unfertilized egg
In bees, drones are
developed from
unfertilized eggs
28-2: Diversity of Arthropods
Diversity of All Animals
About 85% of all known
animals are arthropods
Additional information
http://evolution.berkeley.edu/evolibrary/article/_0_0/arthropods_intro_05
Arachnids
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Spiders, scorpions, mites, and ticks belong to
the class Arachnida
Spiders are the largest group of arachnids
An arachnid has a cephalothorax and an
abdomen with six pairs of jointed
appendages
Arachnids
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Chelicerae [kuh-lis-er-uh] – the first pair of
appendages located near the mouth
(modified pinchers or fangs)
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Pincers are used to hold food, and fangs inject
prey with poison
Arachnids
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Pedipalps – the second pair of appendages
that are adapted for handling food and for
sensing
In male spiders, pedipalps are used to carry
sperm during reproduction
The four remaining appendages are adapted
as legs
Arachnids
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As silk is secreted, it is spun into thread by
structures called spinnerets, located at the
rear of the spider
Crustaceans
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Crustaceans are the only arthropods that
have two pairs of antennae for sensing
Some crustaceans have three body sections,
and other have only two
Crustacean mandibles open and close from
side to side
The blue crab has 3 body sections
Crustaceans
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Class Crustacea include crabs, lobsters,
shrimps, crayfishes, pill bugs, and barnacles
Most crustaceans are aquatic and exchange
gases over gills
Centipedes and Millipedes
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Centipedes and millipedes have tracheal
tubes for gas exchange
Centipedes are carnivorous and eat soil
arthropods, snails, slugs, and worms
These arthropods can bite
Centipedes and Millipedes
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A millipede eats mostly plants and dead
material on damp forest floors
Millipedes do not bite, but they can spray
foul-smelling fluids from stink glands
Insects
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Class Insecta is the largest group of
arthropods
Insects have three body segments and six
legs
Insect Reproduction
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Insects usually mate once during a lifetime
Some insects exhibit parthenogenesis
Most insects lay a large number of eggs,
which increase the chances that some
offspring will survive long enough to
reproduce
Metamorphosis
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Metamorphosis – the series of changes, controlled
by chemical-substances in the animal
Two types of metamorphosis:
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1. Complete metamorphosis consists of four stages:
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Egg
Larva – the free-living, wormlike stage of an insect
Pupa – a period of reorganization in which the tissues and
organs of the larva are broken down and replaced by adult
tissues
Adult
Metamorphosis
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Examples: ants, beetles, flies, and wasps
Complete metamorphosis is an advantage for
arthropods because larvae do not compete
with adults for the same food
Metamorphosis
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2. Incomplete metamorphosis – insects go
through only three stages of development
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Egg
Nymph – hatches from an egg, has the same general
appearances the adult but is smaller
Adult
With each molt, it begins to resemble the
adult more
Grasshoppers and cockroaches undergo
incomplete metamorphosis
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Picture of incomplete metamorphosis