 Most diverse phylum  Most successful of all time  About 1 million species have been identified  = more than 3 times the number of all other animal species combined!!

 Includes insects, crabs, centipedes, and spiders  All have segmented bodies, tough exoskeletons, and jointed appendages

 Provide protection and support  Made of protein and carbohydrate called chitin  Vary in shape, size and toughness  Terrestrial arthropods have waxy covering to prevent water loss

 Appendages: structures such as legs and antennae that extend from the body wall  All are jointed  Include antennae, claws, walking legs, wings, flippers, mouthparts, tails, and other specialized structures  Named for this: arthron means “joint” in Greek, and podos means “foot”

 First arthropods appeared in the sea more than 600 million yrs. Ago  Live in every habitat on Earth: sea, freshwater, land, and air  Evolution has led to fewer body segments and highly specialized appendages for feeding, movement, and other functions

 Use complex organ systems  Feeding: herbivores, carnivores, and omnivores  Bloodsuckers, filter feeders, detritivores, and parasites  Mouthparts modified for chewing, sponging, sucking, and probing

 Respiration  Terrestrial arthropods breathe through network of branching tracheal tubes that extend throughout the body  Air enters and leaves the tubes through spiracles: small openings located on outside of body  Spiders have book lungs: organs with layers of respiratory tissues stacked like a book  Aquatic arthropods use featherlike gills or book gills

 Open circulatory system  Well-developed heart pumps blood through arteries that branch and enter the tissues  Leaves vessels moves through sinuses or cavities  Collects in large sinus surrounding heart  Re-enters heart and is again pumped through body

 Excretion  Terrestrial arthropods use malpighian tubules: saclike organs that extract wastes from the blood and then add them to feces that move through the gut  Aquatic arthropods use diffusion to move cellular wastes from the body to the water

 Well developed nervous systems  Have brains that receive information and send it out to muscles  Two nerves connect brain to a ventral nerve cord  Along nerve cord are several ganglia that coordinate movements of individual legs and wings  Sophisticated sense organs: compound eyes may have more than 2000 separate lenses to detect color and motion very well

 Movement by well-developed groups of muscles made of individual muscle cells that contract and pull on exoskeleton  At each joint, different muscles either flex or extend

 Reproduction  Terrestrial arthropods have internal fertilization  Some put sperm inside female, others deposit sperm packet that female picks up  Aquatic arthropods may have internal or external fertilization

 Exoskeleton does not grow, must be shed as arthropod gets bigger  Molting: shedding of entire exoskeleton and making a new one  Controlled by hormones  Can take several hours  Makes them vulnerable to predators while shell is still soft  Most hide during molting or molt at night

 Arthropods are classified based on the number and structure of their body segments and appendages – particularly their mouthparts

 Mostly aquatic  Includes crabs, shrimps, lobsters, crayfishes, and barnacles  Range in size from small terrestrial pill bugs to enormous spider crabs up to 20 kilograms  Typically have 2 pairs of antennae, 2 or 3 body sections, and chewing mouthparts called mandibles

 Cephalothorax: anterior, fusion of head with the thorax  Thorax: holds internal organs  Abdomen: posterior part of the body  Carapace: part of the exoskeleton covering the cephalothorax

 1st 2 pairs of appendages are antennae covered in sensory hairs  Used as sensory organs, filter-feeding, or swimming  3 rd pair are the mandibles adapted for biting and grinding food  Gills are attached to appendages associated with the cephalothorax

 Decapods: crayfish, lobsters, and crabs  Largest group of crustaceans  Five pairs of legs  1 st pair of legs called chelipeds, bear large claws modified to catch, pick up, crush and cut food  4 pairs of walking legs  Along abdomen are several pairs of swimmerets: flipperlike appendages used for swimming  Final abdominal segment is fused to form a large, flat tail: uropod

 Barnacles  Sessile, have lost their abdominal segments and no longer use mandibles  Outer shell-like covering  Attach themselves to rocks along the shore, in tide pools, surface of marine animals such as whales  Use appendages to capture and draw food particles into mouth

 Includes horseshoe crabs, spiders, ticks, and scorpions  Have mouthparts called chelicerae and two body segments and 4 pairs of walking legs  No antennae  Cephalothorax contains brain, eyes, mouth, and walking legs  Abdomen contains internal organs

 Chelicerae contain fangs used to stab and paralyze prey  Pedipalps used to grab prey  Respire with either book gills or book lungs  Two main classes: Merostomata and Arachnida

 Class Merostomata  Includes horseshoe crabs  Oldest living arthropods: first appeared 500 mya  Not true crabs at all  Anatomy similar to spiders  Have chelicerae, five pairs of walking legs, and long spikelike tail  Can grow to size to frying pan  Common along eastern US coast

 Spiders: largest group of arachnids  Capture food in a variety of ways: webs made of protein called silk, stalk and pounce on prey (turantula), lie in wait then grab  Feed on animals ranging from other arthropods to small birds  No jaws for chewing, must liquefy food to swallow it

 Once prey is caught, fangs inject paralyzing venom  Once prey is dead, spider injects digestive enzymes into the wounds  Spider sucks out tissues into a specialized pumping stomach  Food then moves to the rest of the digestive tract being further broken down by enzymes

 All spiders produce silk even if they don’t spin webs  Stronger than steel!  Used for webs, cocoons for eggs, wrappings for prey  Force liquid silk through spinnerets: organs that contain silk glands  As silk comes out it hardens into single strand  Spinning webs seems to be preprogrammed behavior

 Mites and Ticks: small and often parasitic  Specialized chelicerae for piercing tissue and sucking out blood  Pedipalps are often equipped with claws for holding on to host  Parasitize plants and animals  Can cause itching, painful rashes, and transmit diseases such as Rocky Mtn. spotted fever and Lyme disease

 Scorpions: widespread in warm areas including southern US  Pedipalps enlarged into claws  Long, segmented abdomen has a venomous stinger that can kill or paralyze prey  Chew up prey with chelicerae

 Includes centipedes, millipedes, and insects  Response to stimuli  Compound eyes  Chemical receptors for taste and smell on mouthparts, antennae and legs  Sensory hairs to detect movement  Well-developed ears that hear above human range; found in strange places (behind legs in grasshoppers)

 Adaptations for feeding  3 pairs of appendages for mouthparts including mandibles  Saliva contains digestive enzymes  Bee saliva help change nectar into honey  Glands in bee’s abdomen secrete wax, used to build beehives

 Movement and Flight  Legs used for jumping, walking, capturing and holding prey  Flying insects usually have two pairs of wings made of chitin  Flight has allowed for movement worldwide and wide variety of habitats

 Metamorphosis: process of changing shape and form  2 types: incomplete and complete  Incomplete metamorphosis: gradual change with nymph immature forms  Nymphs lack sexual organs and wings and usually look similar to the adult form  Complete metamorphosis: dramatic change with larval stage and pupa

 Use sound, visual, chemical, and other types of signals  Most communication is for mating  Sound: crickets chirping by rubbing legs together; cicadas buzz by vibrating special membranes on their abdomens  Visual cues: fireflies lighting up  Chemical signals: pheromones used for alarm or alerting other insects and for mating

 Ants, bees, termites, and some of their relatives form complex associations called societies  Societies work together for the benefit of the whole group  Can have more than 7 million individuals  Castes: groups of individuals performing a certain job or role in the society (queen, workers, drones, etc)

 Centipedes: Class Chilopoda  Millipedes: Class Diplopoda  Insects: Class Insecta Order Orthoptera: Crickets, grasshoppers, locusts Order Isoptera: termites Order Hymenoptera: bees, wasps, and ants Order Lepidoptera: butterflies and moths Order Diptera: true flies Order Coleoptera: beetles Order Hemiptera: true bugs Order Anoplura: human louse (lice) Order Odonata: dragonflies Order Dictyoptera: cockroaches and mantids