Arthropods

Chapter 2 Section 2

Arthropods

• What are some examples of common arthropods?– Insects– Spiders– Crabs – Lobsters– Centipedes– Scorpions

Arthropods

• Earth has more species of Arthropods than all of the other animals combined

• Today scientists have identified 875,000 different arthropod species

• There are most likely more that we have not yet identified!

Characteristics of Arthropods

• Phylum Arthropoda

– Invertebrate

– External Skeleton

– Segmented Body

– Jointed attachments• Appendages

Characteristics of Arthropods

• Phylum Arthropoda

– Arthros means “joint” in Greek

– podos means “foot” or “leg”

– Jointed legs are a distinct characteristic

Characteristics of Arthropods

• Phylum Arthropoda– Open circulatory system

• Blood leaves the blood vessels and bathes the internal organs

– Most reproduce sexually

– Most are either male or female

– Most have internal fertilization

Skeleton

• What is an exoskeleton?– Outer skeleton that protects the animal– Helps prevent the evaporation of water

• Waterproof shell

• Why do they need to have a shell that keeps them wet?– Keep from drying out!

Skeleton

• 1st animals to move out of water and onto land

• What permitted the arthropods to move onto land?– Exoskeleton

Skeleton

• What is the material that the exoskeleton is made of?– Chitin

• Chitin:– Long molecules which are built from many

smaller building block – like links in a chain• This is a polymer

– These molecules make chitin tough and flexible

Skeleton

• What happens to the exoskeleton as the animal grows larger?

• – They shed their

exoskeleton

– They grow a new, larger one in its place

• What is the process of shedding called?

– Molting

• After an arthropod molts it is soft for awhile and has less protection from danger

Segmented Bodies

• What are the three segments called?

– Thorax– Abdomen– Head

Segmented Bodies

• This body plan is easiest to see in centipedes and millipedes because they have identical segments

• Where else can we see segments?– Tails of shrimp and lobster

Appendages

• Why do arthropods have appendages?– Give the animal flexibility– Enable it to move

• What are some common appendages?– Wings– Mouthparts– Legs

Appendages

• Tend to be highly specialized tools– Ex: The mouthpart of a crayfish is used to

crush food

– Antenna:• Appendage on the head that contains sense

organs• A crayfish antenna is used for smelling, tasting,

touching, and keeping balance

Appendages

• Other appendages– Legs:

• Walking• Crayfish use their 1st pair of legs which have claws

for catching prey and defense

– Wings:• Used for flying / movement

Origin

• Segmented worms and arthropods – what do they have in common?

– Both have segmented bodies– Have appendages attached to some

segments– Due to these similarities scientists infer that

these two groups have a common ancestor– DNA shows that they are not as close as we

thought

Origin

• Have been on Earth for 540 million years

• 1st arose from the oceans

• Today they live everywhere

• Some are adapted to fresh or salt water – Crayfish– Crabs

Crustaceans• Major groups

– Crustaceans

– Arachnids

– Centipedes

– Millipedes

– Insects

Crustacean

• Crustacean:– Arthropod that has 2 or 3 body sections

– Usually 3 pairs of appendages for chewing

– 5 or more pairs of legs

– Each body segment has a pair of legs or modified legs attached to it

– Only arthropod to have 2 pairs of antennae

Crustaceans

• Most begin their life as microscopic, swimming larvae– Example: crabs, barnacles, and shrimp

• The larvae form does not resemble the adult form

• Metamorphosis:– Process in which an animal’s body undergoes

dramatic changes in form during its life cycle

– Develop from a larvae into an adult

Crustaceans

• Live in nearly any watery environment

• Obtain oxygen through their gills

• Thrive in freshwater, lakes, rivers, and even puddles

Crustaceans

• What and how do they eat?– Eat dead plants and animals– Eat animals they prey on– Some have appendages to stun their prey

• Ex: pistol shrimp

– Eat plantlike microorganisms • Krill

Spiders & Their Relatives

• Arachnid:– Arthropod with only 2 body sections

• Cephalothorax• Abdomen

– Abdomen:• Contains the reproductive organs• Part of its digestive tract

Spiders & Their Relatives

• Have 8 legs

• No antennae

• Use book lungs to breathe – Tiny network of tubes that lead to the

openings of the exoskeleton

Spiders

• All spiders are predators– Most eat insects– Some run their prey down others catch them

in their web

• Have hollow fangs with venom– Turns the tissue into mush

• Most bites do not harm humans

Mites

• Parasites

• Examples:– Chiggers– Ear mites (dogs and cats)– Dust mites

• Allergic to the exoskeleton

• Mites are everywhere– Even in fresh water and the ocean

Ticks

• Parasites

• Live on the outside of a host

• Nearly every kind of land animal has a species of tick that sucks its blood

• Some carry disease– Lyme Disease is spread by deer tick