• 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

• 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 • Tissues swell and put pressure on old

exoskeleton• 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

• 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

• Includes extinct trilobite

• Marine • Have a head &

segmented trunk with one pair of legs on each segment

• Breathe through gills

• Single pair of antenna

• Includes 2 classes --- Xiphosura or Merostomata (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

• Terrestrial• Body divided into a cephalothorax

and abdomen• The cephalothorax usually has six

pairs of jointed appendages     * Four pairs of legs     * Chelicerae or fangs with venom     * Pedipalps

• * No antenna• Breathe by book lungs &/or tracheal

tubes

• 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                          

Adaptations for a predatory life on land1. Book lungs = paired sacs in the abdomen

with many parallel folds that resemble the pages of a book. The folds in a book lung provide a large surface area for gas exchange. (and/or)

2. Tracheae = a system of tubes that carry air directly to the tissues from spiracles in the exoskeleton.

3. Malpighian tubules = hollow projections of the digestive tract that collect body fluids and wastes and carry them to the intestine. After most of the water is absorbed, the wastes leave the body in a nearly solid form with the feces. This helps spiders conserve water.

And/Or4. Coxal glands = organs that remove

wastes and discharge them through openings at the base of some of the legs.

• 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 (extremely small parasitic or free-living)

• Ticks carry Lyme disease & Rocky Mountain Spotted Fever (range in length from a few millimeters to a little over 1inch and are parasitic)

• 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

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

• Terrestrial crustaceans called isopods include pillbugs & sowbugs

• Freshwater members include crayfish & Daphnia (water fleas)

• Have two pairs of appendages on their head that serve as feelers

• Usually have appendages on most other body segments

• At least some of the appendages are branched• All have jaws or mandibles for chewing or

tearing • Known as mandibulates • Have cephalothorax & abdomen • 16 to 20 body segments• Have 10 pairs of jointed appendages • Most breathe through gills • Most have a nauplius larval stage• Aquatic crustaceans often incorporate large

amounts of calcium carbonate into their exoskeleton

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

appendages called cirri

• Live on land in dark places • Have 7 pairs of legs on a segmented

body• Can roll into a ball for protection

• 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 antennule

• 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

• 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

• Know functions of appendages pg. 749• Digestion = food passes through the

esophagus to the stomach, where teeth made of chitin and calcium carbonate grind the food into a fine paste. The paste is mixed with enzymes from the digestive gland then it enters the intestine and the digestive gland for further digestion and absorption. Indigestible material leaves through the anus

• Respiration = as a crayfish walks, its legs circulate water across its gills. Feathery branches on the posterior pair of maxillae also help direct water over the gills. Each gill is covered by an extension of the exoskeleton that is thin enough to permit gases to diffuse across the gill surface.

• Circulation = the dorsal heart pumps hemolymph into several large vessels that carry it to different regions of the body. Hemolymph leaves the vessels and enters the gills, where it exchanges carbon dioxide and oxygen with the water. From the gills, the hemolymph returns to the dorsal part of the crayfish and enters the heart.

• Excretion = water constantly enters the tissues of a crayfish by osmosis. This excess water is eliminated by green glands. The dilute fluid is collected by the green glands leaves the body through a pore at the base of the antennae.

• 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

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

• Single pair of unbranched antenna• Includes 3 classes --- Chilopoda

(centipedes), Diplopoda (millipedes), & Insecta

• Known as myriapods “many feet”• Most are terrestrial • Exoskeleton prevents desiccation

(water loss)

• 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

• 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