arthropda : remaining groups

Question 1

trilobitomorpha

Answer 1

• 22000 species known
• restricted to palaeozoic seas :
  • dominated cambrian and ordovician periods (440 -
  520 MYA)
  • continued to be important to permo-triassic mass
  extinctions 245 MYA
• most benthic - up to 70cm - deposit feeders

Question 2

cheliceriformes

Answer 2

spiders and their kin

• body composed of two tagmata :
  • prosoma ( cephalothorax ) - head and thorax fused
  together
  • opisthosoma ( abdomen )
• no antennae
• presence of chelicerae ( fangs in spiders ) and
  pedipalps

Question 3

cheliceriformes : abundence

Answer 3

• 80,000 living species
• mostly terrestrial and second only to insects in diversity on land
• cambrian marine origin (extinct sea scorpions and extant horseshoe crabs (limulidae) and sea spiders (pycnogonids))
• scorpions produce stalked spermatophores
• male pedipalps are modified for sperm transfer
• scorpion chelae are also on pedipalps