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The Arthropods
Chapter 33
General statistics
Most
numerous and successful phyla
400,000 known plant species
250,000 known non-arthropod animals
Over 1,000,000 species of arthropods.
5 classes of arthropods
General characteristics
Arthropoda:
From
the Greek word arthron
meaning “joint” and poda meaning
“foot”
1) Jointed appendages used for
crawling, swimming, flying, etc.
More characteristics
2. Possess an exoskeleton
•
Made up of protein and chitin
•
Helps to waterproof and prevent water
loss
•
Main disadvantage: exoskeleton does not
“grow” with the organism. Must be shed.
•
molting
3.
Segmented body
4. Well developed nervous systems
5. Open circulatory system
Class Crustacea
 Lobsters,
crayfish,
crabs, shrimp.
 Mostly marine,
some fresh water.
 All have 2 pairs of
antennae on the
head and 2 body
regions.
The crayfish
 Cephalothorax:
fusion of the head and
thorax
 Antennules: first pair of appendages
attached to the head. Shorter of the two
pairs of antennae

Used for touch, taste, and balance
More appendages
 2nd
pair : antennae (long) used for touch and
tasting
 Mandibles (jaws) 1 pair. Used for crushing
food
 Maxillae: 2 pairs. Used to handle food
 Maxillipeds: 3 pairs. Touch, taste, handling
of food
Chelipeds
Large
first legs
where claws are
found.
Used for defense
and grasping
prey.
and more appendages
 Walking
legs (4 pairs)
 Swimmerets :
appendages found on
the underside of the
abdomen.
 Used for swimming
and carrying eggs and
young.
Internal Structure
 NUTRITION
 Food
is caught with the chelipeds, crushed
by the mandibles and passed into
esophagus.
 Food then digested and wastes passed out
the anus.
Excretion
 Wastes
from the blood are removed by the
green glands in the head.
Circulation and respiration
 Possess
a dorsal heart.
 Open circulatory system (no capillaries nor
veins)
 Arteries dump blood into open spaces,
sternal sinus collects old blood and channels
it to gills to pick up oxygen.
 Hemocyanin
= copper containing pigment
in the blood that aids in transport of oxygen.
 Gasses are exchanged at gills:
Nervous system
Well
developed sensory organs
Compound eyes, many sensory
hairs
Statocysts: sacs at the base of the
antennules that aids in balance.
Reproduction
 Separate
sexes. Can determine sex by
looking at first pair of swimmerets.
 Male will have enlarged first pair of
swimmerets to transfer sperm to seminal
receptacle of female during the fall.
 Eggs attach to swimmerets and hatch in the
spring.
 Young stay attached until self sufficient.
Baby crayfish:
Class Chilopoda (centipedes)
 “centipede”
literally means 100 feet
 Usually 30 to 60 legs, can be as many as
350 legs
 A distinct 6 segmented head
 Worm-like body with similar segments.
More centipede facts
 All
body segments have one pair of legs
except the one behind the head and the last
two. Fairly fast crawlers
 Feed on insects using poison claws.
 Usually found in dark damp places

Under logs and rocks, in basements
Class diplopoda (millipedes)
 Literally
1000 legs although no species has
this many legs. World record is 750 legs.
 Usually anywhere from 100 to 300 legs.
 Two pairs of legs per body segment except
for the last two segments. Slow moving
 No poison claws; feed on decaying plant
material.
Class arachnida
 Spiders,
scorpions, ticks, and mites
 Mostly free-living. A few parasitic
 Some are harmful to humans (poisonous
cause disease)
 Mostly helpful

Get rid of pests like mosquitos
Ticks
 Can
cause disease ex.
 Spotted Rocky Mt. Fever
 Lyme Disease
Lyme Disease
 Carried
by deer ticks.
Caused by a
bacterium.
 Usually in wooded
areas of Mid-Atlantic
states and New
England.
spiders

1)
2)

2 body segments
Cephalothorax (6 pairs of appendages)
Adbdomen
No antennae or
Chewing jaws
chelicerae
 First
pair of
appendages
 Also known as the
“fangs” of a spider
 Will inject a poison
into its prey.
pedipalps
 Found
between the
first pair of legs and
the chelicerae.
 Used for sensing
chemicals and
touch
 Used to manipulate
food.
Abdomen appendages:
4
pairs of walking legs
 Book lungs = respiratory organs on
underside of abdomen
 Spinnerets: posterior end of abdomen, used
to make silk for webs and raising and
lowering themselves.
Class insecta
 Most successful class of arthropods:
30 orders
 Live in all habitats
 High reproductive rates (all reproduce
sexually)
 Small in size
 Only invertebrates capable of flight
Why is flight such an
advantage?
 Escape
form enemies
 Search for food
 Allow insects to inhabit environments not
inhabited by other organisms.
 Less competition for natural resources.
3 body regions:
1.
2.
3.
Head (mouthparts, antennae,
eyes)
Thorax (3 pairs of legs, wings)
Abdomen (respiratory
structures)
Specialized structures:
Mouthparts
2 main types:
legs
 Used
for swimming, collecting pollen.
Defense, grasping prey, jumping
Incomplete metamorphosis
 Series
of changes where an insect grows
from eggs to a nymph to an adult
 Nymph = immature form that closely
resembles the adult form except for certain
features.
 Examples: grasshoppers, crickets
Complete metamorphosis
4
stages:
 Eggs, larva, pupa, adult
 Larval stage examples: caterpillars, maggots
 Pupa: cocoon
 Changes are controlled by hormones.
 ex.
Grasshopper (order Orthroptera)
 Head
2
large compound eyes
 3 simple eyes
 1 pair of antennae
 Mouthparts located outside the
mouth(mandible, maxilla, special tonguelike organ)
Thorax
3
separate segments to the thorax with each
possessing a pair of legs
 Each leg has five segments ending in a
clawed tarsus or foot
 1st and 2nd pairs of legs are for crawling.
 Last pair used for jumping
 2 pairs of wings
Abdomen
 Made
up of 10 segments
 Each segment has one pair of spiracles
(openings into air tubes)
 1 pair of tympanum (hearing organs)
 reproductive organs
Female abdomen
Ovipositor
= hard
four pointed
organ at the base
of the abdomen
used to dig holes
for burying eggs.
Harmful effects of insects:
Cause
millions of dollars in crop
damage.
examples:
Corn smut, rootworm, locusts, tent
caterpillars
Images:
Transmit diseases
 Malaria
= transmitted by mosquitoes
 West Nile virus = also mosquitoes
 West Nile link
Destroy property
Cockroaches
termites
moths
Economic value of insects:
 Help
pollinate fruit trees
 Produce honey
 Kill other harmful insects
 Eat dead plant and animal material
Ways to kill insects:
Most
common: insecticides
Trap and sterilize males
Genetic engineering
 Bt corn
Phylum Echinodermata
 Literally
means “spiny-skinned”
 All marine
 Examples:
characteristics
Well
developed coelom
Endoskeleton
Simplest organism showing
embryological formation of the anus
before formation of the mouth.
Radial symmetry
starfish
 Usually
five arms but can possess up to 20
arms
 Extensive water-vascular system
 Water will enter through the sieve plate and
pass through a series of canals into each
arm.
Tube feet
 Small
water filled tubes or projections on
the ventral surface used for locomotion,
respiration, grabbing prey, and digestion.
More starfish facts
 Feed
on clams and oysters
 Skin gills = small finger-like appendages on
the surface of starfish that is a site for
respiration
 Separate sexes

Can regenerate lost arms. An entire new
starfish can grow as long as part of the central
disk is present.
Assignment:
Page
730
1-17,20,21,22,25,26,27,30,32