Arthropoda: Chelicerata (Spiders, Scorpions and Mites)

Subphylum: Chelicerata

• Horseshoe crabs, scorpions, spiders, mites
• Lack antennae
• Chelicerae: segmented pincers that function as mouthparts
• Chel = "claw", Ceros = "horn"
• Muscular pincers: used to inject venom
• 2 main tagmata
• Cephalothorax
• Partially / completely covered by carapace (hard exoskeleton)
• 6 pairs of limbs (4 pairs of legs)
• Chelicerae
• Pedipalps: sensory limbs near the mouth
• handles food, transfers sperm
• Eyes
• Abdomen
• Contains gut and reproductive organs
• May have legs

Class: Arachnids

• Spiders, mites and scorpions
• Mostly terrestrial
• Ocelli: simple eyes
• Fluid feeding predators
• Do not ingest solid particles
• Digest solids into liquid before eating
• Separate sexes

Order: Aranaea

• Spiders
• Tight constriction between cephalothorax and abdomen
• Trachea and/or book lungs
• Spinnerets: Abdominal appendages for spinning silk
• Fluid Feeding: poison glands inject through chelicera
• Silk producing
• Used to catch prey, escape, transport
• Lines burrows and wrap eggs
• Maternal care and complex courtship

Order: Scorpiones

• Pedipalps modified as grasping pincers
• External digestion, drinks fluids
• Courtship: dance to attract mate
• Female broods young underneath cephalothorax
• carries young on her back

Order: Acari

• Mites
• Fused cephalothorax and abdomen
• No obvious segmentation
• 2 or 3 segmented chelicerae
• 0-2 pairs of ocelli
• Diverse ecology
• Predators, detritivores, herbivores, parasites
• Live in soil, water, plants, in and on animals
• Fluid feeders
• But, detritivores eat solids
• Important in decomposition
• Predators in freshwater and soil
• Huge economic importance
• Crop pests Example: Spider mites
• Bio-control agents
• Medically important Examples: Mites, Chiggars, ticks

Class Xiphosura

• Horseshoe crabs
• Compound eyes
• Book gills
• Long terminal spine
• Xiphos = "sword', uros = "tail"
• flips animal rightside up
• Burrows in sand
• Habitat
• Coastal bays
• Moves to deep water in winter
• Food
• Scavengers
• Predators
• Spawn just above tide
• important food for shorebirds
• Planktonic larvae