230 INVERTEBRATE ZOOLOGY 



The Phalangida are commonly called the harvest men or 

 daddy-long-legs. As the latter name implies, the legs are inordi- 

 nately long. Respiration is by means of tracheae. They feed 

 largely on mites. 



The Linguatulida or Pentastomida are arachnids the bodies 

 of which have been so much modified in adaptation to the para- 

 sitic habit that the adults are distinctly wormlike. It is only 

 through the larval stages that arachnidan relationships are 

 evident, for the larva bears two pairs of legs. All but the hooks 

 of these legs become lost in metamorphosis, and these are retained 

 near the anterior extremity as organs of fixation. Numerous 

 genera have been differentiated among these highly modified 

 arachnids. Lungs, respiratory passages, and digestive system 

 are usual seats of infestation. Pentastoma, Porocephalus. 

 Armillifer, and Linguatula are characteristic genera. 



Fig. 110. — A male pycnogonid, Nymphon stroemii, c, chelicerae; o, ovigerous 

 legs; p, pedipalpi; r, rostrum. {After Kingsley, from Hertwig's Manual of 

 Zoology, by Kingsley, courtesy Henry Holt and Co.). 



Class 3. Pycnogonida 



The pycnogonids are small, exclusively marine arthropods 

 which cling to seaweeds and hydroids and at times are dredged 

 in great numbers from deep waters. The body consists of 

 a cephalothorax and vestigial abdomen. The cephalothorax 

 usually bears a terminal suctorial proboscis and seven pairs of 

 jointed appendages. The appendages next to the proboscis 

 bear chelae. Four pairs of appendages are usually used in 

 walking. The third pair of appendages are in some species modi- 

 fied in the male for holding the eggs and are termed the ovigerous 

 appendages. Reproductive organs open on the second segment 

 of certain of the legs. 



Though the abdomen is reduced to a mere vestige, without 

 appendages and unsegmented, it contains two pairs of ganglia. 



