8 



AN INTRODUCTION TO ENTOMOLOGY 



CLASS PAL^OSTRACHA 

 The King-crabs or Horseshoe-crabs 



The members of this class 

 are aquatic arthropods, which 

 resemble the Crustacea in that 

 they breathe by true gills, but 

 in other respects are closely 

 allied to the Arachnida. They 

 are apparentl y with out 

 antenna, the appendages hom- 

 ologous to antenna being not 

 feeler-like. The reproductive 

 organs open near the base of 

 the abdomen. 



The class Palasostracha 

 is composed almost entirely 

 of extinct forms, there being 

 living representatives of only 

 a single order, the Xiphosura, 

 and this order is nearly 

 extinct; for of it there re- 

 mains only the genus 

 Ltmulus, represented by 

 only five known species. 



The members of this 

 genus are known as king- 

 crabs or horseshoe-crabs ; 

 the former name is sug- 

 gested by the great size of some of the species; the latter, by 

 shape of the cephalothorax (Fig. 10). 



The king-crabs are marine; they are found on our Atlantic Coast 

 from Maine to Florida, in the West Indies, and on the eastern shores 

 of Asia. They are found in from two to six fathoms of water on 

 sandy and muddy shores; they burrow a short distance in the sand 

 or mud and feed chiefly on worms. The single species of our coast is 

 Limulus polyphemus. 



Fig. 10. A horseshoe crab, Limulus (After 

 Packard). 



the 



