Arthropods 
Non-Insects

Characteristics

• Makes up 3/4's of all animal species

• Includes insects, spiders, scorpions, millipedes, centipedes, crabs, lobsters, & crayfish

• Arthropod means "jointed foot"

• Jointed appendages (legs, antenna, mouthparts)

• Segmented body with paired appendages on each segment)

• External exoskeleton made of chitin (carbohydrate) & protein for protection & support

• Exoskeleton has 3 layers --- outer waxy layer repels water, middle layer has calcium for extra strength, & inner layer has flexible joints for movement

• Protostomes (blastopore develops into mouth)

• Coelomate (mesoderm-lined body cavity)

• Ventral nervous system

• Open circulatory system

• Specialized sensory receptors & high degree of cephalization

• Have simple or compound eyes & segmented antenna

Movement & Growth

• Muscles occur in bundles & are attached to inside of exoskeleton on each side of joints

• Exoskeleton must be periodically molted (shed) for organism to grow

• Molting called ecdysis

• Molting hormone released & causes epidermal cells to secrete enzymes that digest & loosen inner exoskeleton

• New exoskeleton secreted by epidermal cells flexible at first & must harden so arthropod not vulnerable to predators so often stay in hiding after molting

• Arthropods go through numerous molts

Butterfly Molting Pupal Case

Evolution & Taxonomy

• Evolved from ancestral arthropod with many body segments each with appendages

• Modern arthropod segments fused into larger, specialized structures called tagmata

• Four subphyla 
       * Trilobita - extinct trilobites
       * Crustacea - shrimps, lobsters, crayfish, & barnacles
       * Chelicerata - spiders, scorpions, & ticks
       * Uniramia -centipedes, millipedes, & insects

Subphylum Trilobita
Characteristics

• Includes extinct trilobite

• Marine

• Have a head & segmented trunk with one pair of legs on each segment

• Breathe through gills

• Single pair of antenna

TRILOBITE

Subphylum Chelicerata
Characteristics

• Includes 2 classes --- Xiphosura (horseshoe crab) and Arachnida (spiders, ticks, scorpions, & mites)

• Have a cephalothorax (fused head& thorax) and abdomen

• No antenna

• Simple eyes or ocelli

• Have 6 pairs of jointed appendages:
       * Chelicerae - claws or fangs (1 pair)
       * Pedipalps - used for feeding, walking, sensing, transferring sperm (1 pair)
        * Walking legs - movement (4 pairs)

• Horseshoe crab
       * Marine
       * Not true crabs
       * Fanglike pincers or chelicerae
       * Use book gills to breathe

HORSESHOE CRAB

• Arachnids
       * Terrestrial
       * Eight legs
       * Chelicerae or fangs with venom
       * Ocelli
       * No antenna
       * Breathe by book lungs &/or tracheal tubes

• Spiders
       * Arachnid that feeds on insects (carnivores)
       *  Have oval shaped, unsegmented abdomen
       * Cephalothorax connected by narrow waist to abdomen
       * Have 8 simple eyes or ocelli
       * Fangs pierce prey, inject poison, & suck out body fluids 
       * Pedipalps on head help sense prey & move it to the mouth
       * Open circulatory system
       * Ostia are openings in heart where blood reenters
       * Body cavity called hemocoel
       * Hemocycanin is oxygen-carrying pigment in blood
       * Have silk glands to make silk & spinnerets to release silk for webs
       * Breathe by book lungs & tracheal tubes
       * Malpighian tubules filter wastes & reabsorb water                          
       

GARDEN SPIDER

• Ticks & Mites
       * Parasitic arachnid 
       * Fused cephalothorax & abdomen
       * Most abundant arachnid
       * Need blood meal to molt
       * Mites can damage fruit & feed on dead skin at base of hair follicle
       * Ticks carry Lyme disease & Rocky Mountain Spotted Fever

• Scorpions
       * Have a cephalothorax & long segmented abdomen curled over body
       * Prefer dry regions
       * Poisonous stinger on end of abdomen
       * Breathe through book lungs
       * Pedipalps modified into claws
       * Nocturnal predators

SCORPION

Subphylum Crustacea
Characteristics

• Marine members include shrimp, lobster, copepods, barnacles, & crabs

• Terrestrial crustaceans called isopods include pillbugs & sowbugs

PILLBUG

• Freshwater members include crayfish & Daphnia (water fleas)

DAPHNIA

• All have jaws are mandibles for chewing or tearing

• Known as mandibulates

• Have cephalothorax & abdomen

• Have 10 pairs of jointed appendages

• Breathe through gills

• Barnacles
       * Marine
        * Sessile crustaceans that live in limestone case
        * Filter plankton with 12 appendages called cirri
  

BARNACLE

• Isopods (pillbugs & sowbugs)
       * Live on land in dark places
        * Have 7 pairs of legs on a segmented body
        * Can roll into a ball for protection

• Crayfish
       * Cephalothorax made of 13 fused segments & covered by protective carapace
        * Antennules located on head help in balance, touch, & taste
        * Statocysts - balancing organs at the base of antennules
        * Antenna on head used for touch & taste
        * Maxillae - paired mouthparts that move side to side to tear food
        * Maxillipeds - help hold food
        * Chelipeds - claws used to capture food & for protection
        * Mandibles - jaws that move up & down to crush  food
        * Walking legs - 8 pairs used for movement
        * Swimmerets - under abdomen to swim, gas exchange, & protect eggs/young
        * Abdomen ends in flat segment called telson with flat uropods on each side

CRAYFISH

               * Compound eyes on stalks
               * Chitinous teeth in stomach grind food
               * Wastes leave through anus
               *  Green glands filter wastes from blood & help with salt balance
               *  Open circulatory system with heart to pump blood to gills & body cells
               * Ostia - one way valves allowing blood from dorsal sinus to reenter heart
               * Gills attached to walking legs
               * Separate sexes that mate in fall & sperm stored in seminal receptacle
               *  Eggs attach to swimmerets of female & hatch in several weeks

• Copepods
      * Largest group of crustaceans
       *  Make up most of the marine plankton
       *  Serve as food for many marine animals
       *  Found in freshwater, marine, & moist terrestrial environments

COPEPOD

Subphylum Uniramia
Characteristics

• All have antenna, mandibles (jaws), & unbranched appendages

• Includes 3 classes --- Chilopoda (centipedes), Diplopoda (millipedes), & Insecta

• Known as myriapods

• Most are terrestrial

• Exoskeleton prevents desiccation (water loss)

Class Chilopoda

• Terrestrial centipedes

• Flattened body with longer legs for fast movement

• Have 1 pair of legs per body segment

• Predators

• Mandibles & maxilla for chewing prey (insects & earthworms)

• Claw-like appendages or pincers on 1st body segment that can inject venom

• Can coil up for defense

CENTIPEDE

Class Diplopoda

• Terrestrial millipedes

• Have 2 pairs of legs per body segment

• Rounded body

• Scavengers on decaying vegetation as they burrow through soil

• Roll into ball when threatened & spray noxious chemical containing cyanide

MILLIPEDE