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

Arthropod Coloring

Subphylum Chelicerata

• Includes Class Arachnida) spiders, ticks, scorpions, mites and horseshoe crabs
• Have a cephalothorax (fused head and 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 and 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