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 1 st 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 1 st 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 1 st 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