Zoology 250 (2002) ARTHROPODA (V): Other Subphyla (Other arthropod study images ; click on tree to see full cladogram)

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• 1) SubPh.CHELICERATA (sea spiders, horseshoe crabs, spiders, mites)
  
  a) body generally has 2 tagmata; lack antennae!; have uniramous legs
  b) Cl. PYCNOGONIDA (sea spiders) ~600 marine spp
  
  - typically small bodied (<5 mm) but deep sea & Antarctic species have leg spans > 25 cm!; predators mainly on hydroids
  - very unusual body form: legs make up 50 - 80% of body mass!
  - typically have 1 pair of chelicerae, 1 pair of ovigers, 4 pair of walking legs, a reduced abdomen, and simple eyes
  - have an unusual reproductive biology: males brood embryos

  c) Cl. MEROSTOMATA (horseshoe crabs) ~50 marine spp

  
  - considered 'living fossils' because 400 million-year old fossils resemble living forms so closely; only 4 living species
  - large-bodied predators (to 40 cm) on small, infaunal invertebrates (food shredded or crushed by gnathobases of walking legs)
  - have 1 pair of chelicerae, 5 pairs of walking legs (first 4 with claws), abdominal book gills, and a prominent tail spine
  - the only chelicerate with compound eyes (independently evolved)
  
  d) Cl. ARACHNIDA (spiders, mites & ticks, scorpions, etc.) ~70,000 mostly terrestrial spp; a few marine & freshwater spp
  
  - generally inspire more fear in humans than any other animal group
  - have 1 pair of chelicerae; modified as small pincers (most groups) or hollow fangs for injecting poison (spiders)
  - have 1 pair of pedipalps; may be leg-like & sensory (spiders) or form large pincers (scorpions)
  - 4 pair walking legs (abdomen may have other limbs), simple eyes
  - Or Araneae (spiders); nearly half of all arachnid species
  
  - liquify prey with digestive enzymes & imbibe fluids with a sucking pharynx & stomach
  - have the impressive ability to spin silk from the abdomen
  - some have quite elaborate social & courtship behaviors

  - Or Acari (mites & ticks) >500,000 spp? are everywhere! (marine, terrestrial, aquatic,aerial, subterranean, deep sea, hot springs)

  
  - most (except ticks) are very small (< 1mm); lack tagamata
  - all ingest liquids (from host, or dissolved by saliva)

• 2) SubPh. TRILOBITOMORPHA (extinct trilobites)
  
  a) were once the most numerous arthropods on earth; some reached very large size (>40cm); all thought to be particle feeders
  b) 3 tagmata; head with 1 pair antennae & 4 pair of thoracic-like legs
  c) variable number of thoracic segments with similar biramous limbs
  d) variable number of abdominal segments fused as pygidium

• 3) SubPh. UNIRAMIA (myriapods & insects)
  
  a) 2nd antennae lost, limbs exclusively uniramous, possess a spiracle/trachea system for respiration

  b) SuperCl. MYRIAPODA:

  
  - body has 2 tagmata (head, trunk); the trunk has many similar legs
  - compound eyes are lost

  - Cl. CHILOPODA (centipedes) 15 - 177 pairs of legs; 1st pair bears poison claws; mostly predatory
  - Cl. DIPLOPODA (millipedes): 100 - 700 pairs of legs; adjacent trunk segments fuse yielding 2 pairs of legs per body unit (diplosegment); mostly herbivores

  • c) SuperCl. HEXAPODA (=Insecta):
    
    - body has 3 tagmata (head, thorax, abdomen); thorax bears 3 pairs of walking legs; abdomen lacks limbs
    - 2nd maxillae fuse as labium
    - typically have 1 pr compound eyes & 3 medial ocelli (simple eyes)

    - Cl. APTERYGOTA: insects lacking wings (ametabolous devel.)
    - Cl. PTERYGOTA: winged insects

    
    - SubCl. EXOPTERYGOTA: wing buds are external; mostly hemimetabolous devel. (nymphs resemble adults but lack wings)
    - SubCl. ENDOPTERYGOTA: wing buds arise from internal imaginal discs; holometabolous development (larvae may bear no resemblence to adult; pass through a pupal stage where a radical metamorphosis takes place; eclose as fully formed adult)
    - an extraordinarily successful arthropod group, but very curiously never successfully invaded the sea

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