Biology 3B Laboratory Invertebrates II: Annelida, Nematoda ...

• CLASS ARACHNIDA
This class consists of members that are rather familiar to most. They include spiders, scorpions,
ticks and mites. All members posses a pair of cherlicera, pedipalps and four pairs of walking legs.
o Examine the Cephalothorax of the garden spider Argiope (figure 8) Note the number of
eyes. Identify the chelicerae. They have been modified into fangs for the injection of
poison. Find the pedipalp. What’s its general function? In males, the pedipalps are
modified as an intromittent organ to deliver sperm to the female. How many walking do
spiders have and what body segment (tagmata) are they located?
o Obtain a dissecting scope and examine the ventral abdominal region of Argiope. Look for
the lung slit at the anterior portion of the abdomen. Towards the posterior end of the
abdomen, you will notice three pairs of spinnerets on a raised surface responsible for silk
production.
Figure 8: Ventral view of Argiope
o Examine a scorpion. The pincers are the pedipalps. Note the stinger with venom sac at
the distal portion of the abdomen.
o Examine the slide of a tick. These are ectoparasites on various vertebrates. Many can
transmit diseases such as Lyme disease and Rocky Mountain spotted fever.
o Examine the slide of a mite. Mites are some of the smallest archnids.
Biology 3B Laboratory Invertebrates II Page 8 of 17