Arthropods Chapter 36 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 Compound eye Open circulatory system Protection, support, prevents desiccation 3 layers excreted by epidermis Made of chitin Compound eye Optic nerves send impulse to the ventral nerve cord Open circulatory system

Molting: Video 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 Video

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 Trilobita: (trilobites) Extinct! Crustacea: (shrimp, lobster, crayfish, pill bugs, barnacles) Chelicerata: (spiders, scorpions, ticks, horseshoe crab) Myriapoda: (centipedes, millipedes) 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 CaCO3 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: Terrestrial: Isopods 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 – WEAR CORRECT SHOES! Video

External Structure Two major sections: Cephalothorax: two tagmata Head – 5 segments Thorax – 8 segments posterior to head Carapace – dorsal exoskeleton Abdomen: 7 segments Telson – 7th 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 tailflips

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: Video Sexual: 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 Video

Female Male

Subphyla Chelicerata & Mryiapoda Section 36.3

Subphyla Chelicerata Examples: spiders, scorpions, mites, horseshoe crab Typically 6 pair of appendages 1st 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 Coxal glands = organ that removes wastes & discharges through openings at base of legs OR

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

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

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

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