Phylum ARTHROPODA                                 scorpion.gif (5223 bytes)




Learn more about chelicerates  from the University of California Museum of Paleontology website.


Subclass Eurypterida

  • UCMP eurypterids   [Fig. 23.7]: Paleozoic "water scorpions"
eurypterid003P.gif (97411 bytes) Eurypterus remiped lacustris; Upper Silurian; semicircular carapace of head region (prosoma) with crescentic eyes: from Bertie Formation of Ridgeway Ontario; click on picture to enlarge; photos courtesy of BIODIDAC

Subclass Xiphosura

Limulus031P.gif (93574 bytes)Chel035p.gif (165596 bytes)
Dorsal and ventral views of Limulus; click on pictures to enlarge; photos courtesy of BIODIDAC


arachnids from UCMP

  1. spiders [Fig. 23.12, 23.13];
  2. scorpions [Fig. 23.11]
  3. acari: mites [Fig. 23.14] and ticks [Fig. 23.16]; ; entomology image gallery from Iowa state has photographs and movies of ticks
  4. daddy long legs

some characteristics

  1. chelicerae: preoral pincers--poisonous fangs in spiders
  2. mainly carnivorous
  3. mites and ticks are ectoparasites-transmit Lyme disease, Rocky Mounted spotted fever, etc.


Lactrodectus mactans, Black Widow Spider, photograph by George W. Robinson,  California Academy of Sciences 

scorpion, photograph by Dr. Antonio J. Ferreira, California Academy of Sciences. 

Class PYCNOGONIDA: sea spiders [Fig. 23.16]



  1. biramous appendages [Fig. 23.17]
  2. two pair of antennae
  3. one pair of mandibles
  4. 40,000 species
  5. learn more from Paisley University


  1. Class Malacostraca
    1. decapods: lobsters [Fig. 23.18], crayfish [Fig. 23.19], crabs, shrimp, krill
    2. amphipods 
    3. isopods (mostly aquatic, but includes pill bugs, the only terrestrial crustaceans [Fig. 23.22])
  2. Class Branchiopoda
    1. brine shrimp, cladocerans (water fleas-Daphnia) [Fig. 23.23]
  3. Class Copepoda: "the sheep of the sea" [Fig. 23.1]
  4. Class Cirripedia: barnacles [Fig. 23.24]

    Balanus sp.; acorn barnacles; Photograph by Sherry Ballard, California Academy of Sciences.  Pollicipes polymerus; Leaf Barnacle. Photograph below left by E. Eugenia Patten, California Academy of Sciences. Photograph below right by Sherry Ballard, California Academy of Sciences

Subphylum UNIRAMIA

Class DIPLOPODA - millipedes [Fig. 24.3a]

  1. two pairs of legs per segment
  2. body round in cross section
  3. mainly herbivorous, also scavengers
  4. many can secrete HCN (hydrogen cyanide)
  5. millipedes, centipedes, and two obscure classes are sometimes grouped together as myriapods
  6. photograph by Jo-Ann Ordano, California Academy of Sciences.

Class CHILOPODA - centipedes [Fig. 24.3b]

  1. one pair of legs per segment
  2. carnivorous
  3. appendages of first trunk segment modified into poison fangs
  4. photograph by James T. Johnson, California Academy of Sciences. 

Class HEXAPODA (or Insecta) [fig. 27.12]

Orders classified by mouthparts--more than 25 orders are recognized, including

  1. Thysanura: silverfish
  2. Odonata: dragonflies
  3. Orthoptera: grasshoppers and crickets
  4. Blattaria: cockroaches
  5. Isoptera: termites, social insects
  6. Phthiraptera: lice
  7. Coleoptera: beetles; entomology image gallery from Iowa state has photographs and movies
  8. Hymenoptera: ants, bees, wasps: social insects, pollination
  9. Lepidoptera: moths and butterflies, pollination
  10. Siphonaptera: fleas
  11. Diptera: flies

For more information



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