Phylum Arthropoda

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http//www.tolweb.org/Arthropoda/2469
mandibulata
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Phylum Arthropoda

• Subphylum Trilobita
• Common 500 mya (4000 spp) but extinct by 225 mya
• Each body segment had a biramous appendage (inner
  for walking)
• 3 body tagma
• Compound eyes with ommatidia

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Trilobites flourished for 270 million years. They
died.
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Subphylum Chelicerata

• Include spiders and mites and daddy LL,
  scorpions, horseshoe crabs
• Lack antennae
• 1st pair of appendages on the prosoma the
  chelicerae (adapted for feeding)

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Class Xiphosura Horseshoe crabs

• 4 spp, all marine
• Not true crabs (i.e., not crustaceans)
• head thorax prosoma or cephalothorax
• appendages of opisthosoma flattened to become
  book gills for gas exchange

Telson
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Class Arachnida

• Terrestrial
• Orders spiders, mites, ticks, scorpions, ddll
• 4 pairs of walking legs, one pair of pedipalps
• Head and thorax fused prosoma
• In ticks the prosoma and opisthosoma fuse
• carapace

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Lymes Disease
Order Acari The ticks

• deer tick Ixodes scapularis is a vector for the
  spirochete, Borrelia burgdorferi, from
  white-footed mice (reservoir host) and people

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Order Scorpiones

• Most ancient arachnid (and therefore most
  primitive terrestrial arthropod)
• Also the largest arachnid is a scorpion (18cm)

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Class Arachnida, Order Scorpiones
A delicacy in Bankok, Thailand
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Opisthosoma
Mesosoma
Prosoma
Metasoma
Eyes
Chelicera
Aculeus
Telson
Chela
Pedipalp
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Class ArachnidaOrder Aranea (Spiders)

• Book gills internalized book lungs
• Spiracles and trachea
• Gas exchange does not require blood
• Spiders are specialized predators
• Poison glands, hollow chelicerae
• Silk glands, web building
• Spinneret are modified appendages
• 7 separate silk glands make different kinds of
  silk

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book lung
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O. Pseudoscorpiones
No stinger
Dispersal by phoresy (hitchhike on houseflies)
Poison in chelae for immobilizing prey
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Order Amblipygi

• First legs held out while they scurry sideways
• serve as tactile and chemoreceptors

Tailless whip scorpions are common in Costa Rica
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Order Opiliones
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Subphylum Mandibulata

• Class Myriapoda
• Order Chilopoda
• Order Diplopoda
• Class Insecta (Hexapoda)
• 33 orders
• Class Crustacea
• 6 subclasses

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Myriapoda

• 1st head segment bears antennae
• 2nd head segment vestigial (no antennae)
• In crustacea this segment bears 2nd pair of
  antennae
• Gas exchange by trachea, spiracles on each body
  segment
• Not closable, risk of water loss
• Cuticle not waterproof more water loss
• Excretion by malpighian tubules
• Repugnatorial glands on ventrum

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Order Chilopoda - centipedes
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• Uniramous appendages, one per segment
• Spiracles cannot be closed to control water loss

Claws (modified legs) with poison glands for
immobilizing prey
mandibles
cephalon
Non-locomotory anal legs Defensive Sensory Aggress
ive
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Diplopoda

• Diplosegments give the appearance of 2 pairs of
  legs per segment
• Lack poison claws
• Some produce cyanide defensive secretions