CHAPTER XIX 



Order 



Acarina 



THE ARACHNOIDS 



CLASSIFICATION or THE ARACHNOIDEA 

 Family Subfamily Genus 



Trombidiidae 

 Gamasidae 



Tyroglyphidae 

 Sarcoptidae 

 Demodicidae 

 Tarsonemidae 



Argasinae 



Species 



Ixodidae 



Ixodinae 



Pentastomida 



The class Arachnoidea and the class Insecta belong to the phylum 

 Arthropoda. This phylum contains a greater number of species than 

 does any other phylum. 



While the lobsters, crabs and water fleas, which belong to the class Crustacea, are 

 important zoologically, they are of very slight importance medically. Besides the 

 Crustacea we have the thousand-legged worms or Myriapoda. 



The different classes of Arthropoda resemble the segmented worms 

 but have as distinction the possession of jointed appendages which 

 proceed from the somites in pairs. Some of the pairs of limbs are for 

 locomotion; at times, certain ones may be specialized for food taking. 



The somites or divisions of the body have a chitinous exoskeleton. 



334 



