Arthropods

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Arthropods

• Jointed-legged invertebrates

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Arthropod Characteristics

• Metamerism with tagmatization
• Chitinous exoskeleton
• Paired-jointed appendages
• Growth with ecdysis (molting)
• Ventral nervous system
• Open circulatory system
• Complete digestive tract
• Malpighian tubules for excretion

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Evolutionary Significance

• Protostomes
• Schizocoelous development
• Paired ventral nerve cord
• Loss of internal metamerism
• Increased tagmatization (specialization of
  segments)

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Terrestrial Dominance

• Minimize water loss
• Exoskeleton
• Respiratory system development
• Advanced excretory system
• Greater ability for movement
• Exoskeleton attaches strong muscles
• Support

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Exoskeleton

• Major reason for success of this group!
• Provides
• Support
• Protection
• Prevention of dehydration
• Sites for muscle attachment

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Exoskeleton Structure

• Epicuticle (outer layer)
• Water tight
• Barrier
• Procuticle (inner layer)
• Made of chitin
• Allows for protection
• Forms joints

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Ecdysis

• Shedding or molting of exoskeleton
• New exoskeleton is soft
• Tanning (sclerotization) must take place to make
  outer layer of procuticle hard

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Metamorphosis

• Change in body form from immature (larval) stages
  to adult forms
• Reduces competition between stages for
• Food
• Living space
• Larval forms often occupy different habitats than
  the adults do

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Taxonomy of Arthropods

• 4 subphyla
• Trilobitomorpha (all extinct)
• Chelicerata
• Crustacea
• Uniramia

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Trilobitomorpha

• Trilobites
• All extinct
• All marine
• 3 sections

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Chelicerata

• Class Merostomata
• Horseshoe crabs
• Water scorpions (eurypterids)
• Class Arachnida
• Spiders
• Mites
• Ticks
• Scorpions
• Class Pycnogonida (sea spiders)

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Chelicerate Characteristics

• Two-part body
• Opisthosoma
• Chelicerae (1st pair of appendages forms
  feeding palps or fangs)
• Pedipalps (2nd pair of appendages)
• Cephalothorax (prosoma)
• Book lungs or book gills

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Crustacea

• Class Malacostraca
• Shrimp, lobsters, crayfish
• Isopods (wood lice roly poly)
• Amphipods
• Class Branchiopoda
• Fairy shrimp, brine shrimp
• Water fleas

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• Class Copepoda
• Cyclops (freshwater)
• Class Cirripedia
• Barnacles
• Sacculina parasite of crabs

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Crustacean Characteristics

• 2 pairs of antennae
• Biramous appendages (Y-shaped)
• Segments are serially homologous

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Uniramia

• Class Diplopoda (millipedes)
• Class Chilopoda (centipedes)
• Class Pauropoda
• Class Symphyla
• Class Hexapoda (insects)

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Insect Locomotion

• Flight
• Walking (3 legs on ground at all times)
• Running (Can run on 2 legs)
• Swimming (legs modified as paddles)
• Jumping (saltatory locomotion)

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Insect Respiration Circulation

• Respiration
• Tracheae spiracle system
• Circulation
• Modified open circulatory system
• Some vessels
• Primitive Heart

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Nervous System

• Johnstons organs (hearing - on antennae)
• Tympanic organs (hearing on legs or body)
• Compound eyes (facets ommatidia fused)
• Simple eyes (ocelli)

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Metamorphosis
Type Appearance Young called
Ametabolous larvae look like adults, just smaller instars
Paurometabolous Specific number of molts Nymphs (land) Naiads (water)
Holometabolous Young very different from adults Larvae
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Economic Impact of Arthropods

1. Name one effect each major group has on mankind
   (good or bad).
2. For insects, list 4 good things that they do and
   4 bad things that they are responsible for.