Chapter Thirteen 



ARACHNOIDEA 



1. XIPHOSURA (King Crabs) 



2. PYCNOGONIDA (Sea Spiders) 



3. ARACHNIDA (Spiders) 



(Not marine — omitted in this book) 



XIPHOSURA 



(King Crabs) 



Although frequently grouped with the Crusta- 

 cea, the Xiphosura are probably more closely related 

 to the Arachnida (Spiders), although perhaps they 

 should better be placed in a group by themselves. 



The Xiphosura form a group of great geological 

 antiquity, closely related to the Trilobites, which 

 lived in the seas of Palaeozoic times, millions of 

 years ago. 



Limulus polyphemus Linne (King Crab; Horse- 



shoe Crab) 



Fig. 42, 43 



This conspicuous animal is found all along the 

 coast from Maine to the Gulf of Mexico. It prefers 

 sandy and muddy associations in bays and harbors 

 where the salinity is not as high as in tL„ open 

 ocean. 



