Arthropods Chapter 36 Phylum Arthropoda Section 36 1

Arthropods Chapter 36

Phylum Arthropoda Section 36. 1

Arthropods • Examples: lobsters, crabs, spiders, millipedes, centipedes, insects • Arthropod means “jointed foot” – Appendages: body segments with jointed extensions • Used in feeding, moving, & mating

Characteristics: • Exoskeleton – Protection, support, prevents desiccation – 3 layers excreted by epidermis • Compound eye – Optic nerves send impulse to the ventral nerve cord • Open circulatory system

Molting: • Periodic shedding of the exoskeleton to allow growth • Few day process to develop hard exoskeleton – extremely vulnerable times! • Hormone, pressure, and enzyme induced – enzymes digest old exoskeleton while synthesizing new one

Evolution: • 545 million years ago – All from a common ancestor • Tagmata: fused segments that perform a specialized function of modern arthropods • 5 subphlya

Classification: 5 Subphyla 1. Trilobita: – • (trilobites) Extinct! 2. Crustacea: – (shrimp, lobster, crayfish, pill bugs, barnacles) 3. Chelicerata: – (spiders, scorpions, ticks, horseshoe crab) 4. Myriapoda: – (centipedes, millipedes) 5. Hexapoda: – (insects, springtails) Page 725

Subphylum Crustacea Section 36. 2

General Information: • • “Crusta” means shell Most are aquatic Defining characteristic = 2 pairs of antennae Exoskeleton: – Made up of chitin (protein) or Ca. CO 3 – Carapace has waxy coating – 16 to 20 body segments that fuse to form tagmatas

General Information: • Many have mandibles – jawlike mouthparts • Usually each segment has at least 1 pair of appendages • Open circulatory system • Many respire with gills (aquatic only) • Nauplius – Free swimming larvae

Crustacean Diversity • Aquatic: – Plankton – collection of small animals that drift near the surface of the water • Copepods (crustaceans) are a part of plankton – – – Water flea Barnacles Shrimp Lobster Crabs Crayfish • Terrestrial: Isopods – Pill and sow bugs – Lose water quickly

Crayfish • Decapods – “ten feet, ” five pairs of legs

THIS IS WHAT WE WILL BE DISSECTING ON MONDAY – WE CORRECT SHOES!

External Structure • Two major sections: – Cephalothorax: two tagmata • Head – 5 segments • Thorax – 8 segments posterior to head • Carapace – dorsal exoskeleton – Abdomen: • 7 segments • Telson – 7 th segment, – flat paddle at posterior

Appendages: • Antennules – touch, taste, equilibrium • Antennae – touch, taste • Mandible – chewing • Maxilla – manipulate food, draw water over gills • Maxilliped – touch, taste, manipulate food

• Cheliped (claws) – capture food, defense • Walking legs – locomotion over solid surfaces • Swimmeret – create water currents, transfer sperm (male), carry eggs and young (female) • Uropod – propulsion during tail flips

Digestion: • Digestive System: mouth esophagus stomach enzymes secreted by digestive gland intestine & digestive gland anus

Respiration: • Respiratory System: – gills – Base of each walking leg under carapace – Diffusion of gases

Excretion: • Excretory System: green glands – Acts like a kidney – Eliminate excess water due to hypotonic environment

Circulation: • Circulatory System: – open system baths organs in hemolymph – Pumping organ: heart (dorsal)

Neural Control: – Brain = pair of ganglia above esophagus – Ventral nerve cord – Sensory hairs on exoskeleton – 2, 000 light sensitive units on each eye – Statocyte at base of antennae for balance

Reproduction: Mate in fall: – Male’s first 2 hollow legs transfer sperm – Female holds sperm until eggs laid, then fertilize; mated previous fall – Eggs laid in spring (100) – carried by female on swimmerets 6 -8 weeks; “berried” – regenerate missing parts

Male Female

Subphyla Chelicerata & Mryiapoda Section 36. 3

Subphyla Chelicerata • Examples: spiders, scorpions, mites, horseshoe crab • Typically 6 pair of appendages – 1 st pair = chelicerae (modified pincers or fangs) Video

Class Arachnida: • Arachnids include spiders, scorpions, mites, and ticks • Cephalothorax has 6 pairs of jointed appendages: – one pair of chelicerae (pincers or fangs) – one pair of pedipalps (aid in holding food & chewing) – Four pairs of walking legs

Anatomy of a spider: • Chelicerae = modified fangs • 8 simple eyes • Spinnerets = produce silk

Respiratory System • Book lungs = paired sacs with parallel folds • Tracheae = system of tubes carrying air directly to tissues – Air in through spiracles in exoskeleton Some have one or the other Some have both!

Excretory System • Malpighian tubules = hollow projections of digestive tract – Collect body fluids & waste – Waste leaves as feces – Helps conserve water in spider

Feeding: • Use webs to capture prey • Inject venom to paralyze animal • Two harmful spiders to humans = black widow & brown recluse

Reproduction: 1. Transfer of sperm to tip of pedipalps 2. Sperm place into seminal receptacles on female 3. Male flees to avoid being eaten 4. Eggs fertilized as passed out of female 5. Fertilized eggs into silken case 6. Female carries eggs or attaches to plant 7. Young spiders hatch in two weeks

Scorpions • Large, pincerlike pedipalps in forward position • Large stinger on last segment of abdomen curled over body – Hunt insects & spiders at night – Inject venom into prey video

Mites • Completely fused cephalothorax & abdomen • Many are free living, some are parasitic • Causes mange in dogs

Chiggers • • Larvae of harvest mites Break vertebrae skin, feed on blood Causes swelling & itching Can attack humans

Ticks • Many parasitic • Pierce host’s skin, feed on blood • Transmits bacteria & microorganisms – Lyme disease – Rocky Mountain spotted fever

Subphylum Myriapoda • • • Myriapods = “many feet” Examples: millipedes & centipedes First animals on land Segmented bodies Live in damp environments

Class Diplopoda • Examples: millipedes • Round bodies • Appendages: – Two pair of legs on each segment – Short antennae – Two groups of simple eyes • When threatened: coil up & secrete noxious fluid with cyanide • Food source: decaying plant material

Class Chilopoda • Example: Centipedes • Flat bodies • Appendages: – – Long, jointed legs Poison claws Long antennae Two clusters of simple eyes • Prey = earthworms, insects, NOT humans! Video