Arthropods 

Characteristics

• Makes up 3/4's of all animal species -total number of arthropod species is MORE than all other species combined

• Includes insects, spiders, & crustaceans

• Arthropod means "jointed foot" - all arthropods have jointed appendages

• Segmented body

• Exoskeleton for protection & support
• Exoskeleton is shed during molting

• Open circulatory system

• Compound eyes (has many individual units)

• Excretory structures called Malpighian tubules

• Wings in many groups
• Respiration using spiracles and trachae

Segmentation

More obvious in larval forms, adults have fused segments -----> Head | Thorax | Abdomen

Some have a fused head and thorax -- the cephalothorax

Taxonomy

Subphylum Chelicerata

• Includes (Class Arachnida) spiders, ticks, scorpions, mites and horseshoe crabs

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

• No antenna

• Spinnerets in spiders make webs

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

 

Subphylum Crustacea Marine members include shrimp, lobster, barnacles, & crabs Terrestrial crustaceans called isopods (pillbugs or rollypollys) Freshwater members include crayfish and daphnia All have mandibles for chewing or tearing Have cephalothorax & abdomen Lobsters and large custraceans are called Decapods Barnacles are sessile (don't move) Have 10 pairs of jointed appendages Breathe through gills Crayfish Dissection covers more on the Crayfish Anatomy

Subphylum Uniramia - Insects and their Relatives

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

Class Chilopoda

• Centipedes (predators)
• Name means "100 legs"

• Flattened body

• Have 1 pair of legs per body segment

• Pincers can inject venom
  

Class Diplopoda

• Millipedes

• Name means "1000 legs"

• Have 2 pairs of legs per body segment

• Rounded body

• Scavengers or herbivores

Class Insecta

• 3 pairs of legs
• 3 body parts - head, thorax, abdomen
• Wings in most
• All appendages attach to the thorax
• 9-11 segments in abdomen
• Mandibles for chewing

Insect Life Cycle

Metamorphosis - dramatic physical change

Complete metamorphosis: Larva --> pupa ---> adult (example: butterflies)
Incomplete metamorphosis: Egg --> nymph --> adult (example: crickets)

Social Insects: Honeybees (workers, queen, drones). Termites, some wasps

Queen: Lays eggs (1 queen per hive)
Drones: a few males to fertilize eggs
Workers: all infertile females