arthropods chapter 2 section 2. arthropods what are some examples of common arthropods? –insects...
TRANSCRIPT
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