The Arthropods

• Phylum Arthropoda includes lobsters, spiders, scorpions, millipedes, and insects. It contains over 1,000,000 species, which is a lot, but scientists believe that only 1/10th of the species have been discovered. It is the most abundant of all the animals. 
• Why should we study this phylum? They live virtually everywhere and their influence upon man and the environment cannot be ignored. They can destroy crops; produce things like wax, drugs, and silk; help maintain cross fertilization; transmit deadly diseases; and some, like spiders, eat mosquitoes!
• Characteristics of phylum arthropoda:
• They have an exoskeleton.





Scorpion's Exoskeleton



• These are made primarily by chitin, a polysaccharide with strong hydrogen bonds.
• Because the exoskeleton is non-living and cannot grow, once the arthropod outgrows their home, they must molt, or shed its covering.
• Enzymes are produced to eat away at the inside of the old exoskeleton while a new exoskeleton is produced underneath the old one.

A scorpion molting





• They have jointed appendages.
• Arthropoda means “joint-footed”
• The muscles of the arthropod move the limbs from within its exoskeleton.
• Variety or forms and functions: 
• spider/grasshopper: jumping and locomotion
• crabs and lobsters: defense
• sensory reception, chewing food, sexual reproduction, etc.
• Body segmentation.
• Arthropods have three body segments:
• Head and thorax (cephalothorax)
• Abdomen

• Open circulatory system
• Dorsal heart

• Ventral nervous system
• Two ganglia joined into a ventral nerve cord. Protected by not only the exoskeleton, but also the bulk of the animal’s body. 
• Near the appendages for command and coordination.

• Antennae: appendages in the head region that provide taste, smell, and touch.
• Sensory bristles
• Eyes: compound (thousands of individual lenses) or simple (one lens)
  
  

  

  Compound Eyes