 There are more species in the Phylum Arthropoda than in all the other animal phylums combined. (There are over 1 million species of arthropods that have been described. However the total number of arthropods may be as high as 1 billion billion.)

 Three characteristics shared by all arthropods are: 1.
exoskeleton 2.
3.
segmented body jointed appendages (which includes walking legs, claws, antennae, and wings.)

 The exoskeleton provides protection from being eaten by animals and from drying out.
-The exoskeleton can bend at the joints.
-The exoskeleton is nonliving and cannot grow, so the animals must molt.
 Molting is the shedding of the exoskeleton that occurs at regular periods as the arthropod grows.

 Open circulatory system (the blood is not contained within small tubes)  Blood is pumped from the heart into the space of the arthropods body  The blood of arthropods carries food but not oxygen throughout the body.
 Complete digestive tract  They have any of 3 special respiratory organs: gills (Crab), book lungs (spider), or tracheal tubes (grasshopper)

 They have 3 main body parts: 1. Head - first part of body and contains sense organs.
2. Thorax or chest - middle body part with walking legs attached.
3. Abdomen - last body part containing reproductive and digestive organs.

 Metamorphosis is a series of distinct changes in form through which an organism passes as it develops from an egg to an adult.
 Reduces competition between stages for  Food  Living space

 Two types of metamorphosis:  Incomplete metamorphosis is where insects pass through 3 stages of development:  Egg (female lays eggs in a hole she has dug.
 Nymph is an immature form that looks like a small adult.
 Adult is an animal that has grown and developed enough to reproduce.
example: grasshopper, cricket, termites, dragonflies

 Complete metamorphosis is where insects pass through 4 stages in its development : 
Egg
 Larva is an insect in the worm like stage. Example: caterpillar, mealworm (Larva hatch from the egg and immediately begin eating a great deal and growing.)  Pupa is the third stage that occurs inside a cocoon. (Within the cocoon the tissues of the larva reorganize to form the adult insect.) 
Adult
example: most insects, butterfly, ants, bees, moths

 Sexual Reproduction

EVOLUTION

 Myriapoda (centipedes, millipedes)  Hexapoda (insects)  Chelicerata (Spiders, ticks)  Crustacea (Lobsters, Crabs)  Trilobita (all extinct)

 “myriapod”- means many-footed  2 body parts  Head  Trunk- contains many paired appendages  Use tracheae for respiration

 4 classes:  Class Chilopoda- centipedes  Class Diplopoda- millipedes  Class Pauropoda- pauropods  Class Symphyla- symphylans

 Six legs  3 body parts- head, thorax and abdomen with appendages on head and thorax

 Classes:  Class Insecta-Beetles, Butterflies  Class Entognatha- Mayfly

 Horseshoe crabs, spiders, ticks and mites, scorpions, and sea spiders.
 Have two main body parts  Cephalothorax – 6 pairs of appendages that include a pair of licerae (mouthparts), a pair of pedipalps, and 4 pairs of walking legs.
 Abdomen  No antennae  Suck liquid food from prey

 3 classes:  Class Merostomata- horseshoe crabs  Class Pycnogonida- Sea spiders  Class Arachnida- spiders, scorpions

 Mainly marine, some freshwater and terrestrial  Two pairs of antennae (first antennae)  One pair of mandibles  Gills for respiration  16-20 segments (some can have 60 or more)

 6 classes:  Class Remipedia- remipede  Class Cephalocarida- cephalocarid  Class Branchiopoda- daphnia, fairy shrimp  Class Ostracoda- copepod  Class Maxillopoda- fish louse  Class Malacostraca- lobsters, crabs, krill

 They have been extinct for 200 million years.
 Dorsoventrally flattened bottom dwellers  Scavengers  Could roll up their bodies  2-67cm in length