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 Subphyla1. 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 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:

– 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 WEWILL BE DISSECTINGON MONDAY – WECORRECT 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 – 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 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

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)

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 otherSome 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 pedipalps2. Sperm place into seminal receptacles

on female3. Male flees to avoid being eaten4. Eggs fertilized as passed out of

female5. Fertilized eggs into silken case6. Female carries eggs or attaches to

plant7. 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