Arthropods

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Arthropods

• Chapter 36

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Phylum Arthropoda

• Section 36.1

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Arthropods

• Examples lobsters, crabs, spiders, millipedes,
  centipedes, insects
• Arthropod means jointed foot
• Appendages body segments with jointed extensions
• Used in feeding, moving, mating

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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

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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

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Evolution

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

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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

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Subphylum Crustacea

• Section 36.2

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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

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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

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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

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Crayfish

• Decapods ten feet, five pairs of legs

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

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Appendages

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

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• 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

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Digestion

• Digestive System mouth ? esophagus ? stomach ?
  enzymes secreted by digestive gland ? intestine
  digestive gland ? anus

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Respiration

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

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Excretion

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

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Circulation

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

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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

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Reproduction

• Mate in fall
• Males 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

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Male
Female
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Subphyla Chelicerata Mryiapoda

• Section 36.3

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Subphyla Chelicerata

• Examples spiders, scorpions, mites, horseshoe
  crab
• Typically 6 pair of appendages
• 1st pair chelicerae (modified pincers or fangs)

Video
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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

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Anatomy of a spider

• Chelicerae modified fangs
• 8 simple eyes
• Spinnerets produce silk

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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!
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Excretory System

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

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Feeding

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

Video
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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

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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
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Mites

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

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Chiggers

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

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Ticks

• Many parasitic
• Pierce hosts skin, feed on blood
• Transmits bacteria microorganisms
• Lyme disease
• Rocky Mountain spotted fever

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Subphylum Myriapoda

• Myriapods many feet
• Examples millipedes centipedes
• First animals on land
• Segmented bodies
• Live in damp environments

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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

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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