Subphylum Chelicerata: Class Arachnida

General Characteristics

All have mouthparts called chelicerae (appear as claws or fangs)

Most are completely harmless (some have painful stings, transmit diseases, or can kill you) 

Like insects they have small, compact bodies and long, delicate limbs, but they are not insects. 

Here are the characteristics that separate them: 

4 pairs of walking legs 

Bodies divided into two major segments (cephalothorax and abdomen)

No antennae or mandibles

Respiration by book lungs 

Usually 4 pairs of simple eyes 

 

Class Arachnida

• Characteristics
• 6 pairs of appendages:
• one pair of chelicerae (with poisonous fangs used to paralyze prey)
• one pair of pedipalps used for sensory reception and in males to transfer sperm
• 4 pairs of walking legs

• Nutrition:
• All spiders spin silk used for containing eggs, restraining prey, or building a web.
• Originates as a liquid protein and is released through organs called spinnerets. 
• Not all spiders catch prey in their webs. Some prowl on the group and ambush their prey.
• Once a spider has they prey, they immobilize them with a bite from the chelicerae and inject digestive juices into the victim. 
• The spider then sucks up the partially digested tissues using its stomach and pharynx.

• Respiration:
• Only arachnids have and use book lungs for respiration. 
• Air enters the spider through a slit in the abdomen and flows between folds of the book lungs where gas is exchanged.
• Reproduction:
• The sexes are separate. Females are often larger.
• Male places his sperm in a tiny web sac and stores it in special cavities of his pedipalps. He then transfers it to the female after a courtship offering of food.
• In some species, the female will eat the male after mating.
• As she lays her eggs, they are fertilized by the stored sperm.