PHYLUM ARTHROPODA 385 



It is convenient to mention at this point three groups of pe- 

 culiar animals that are often placed in the class Arachnida: 

 (1) the Pycnogonida (Pantopoda), (2) the Tardigrada, and 

 (3) the Pentastomida. The Pycnogonida (Fig. 329) are marine 

 animals with small bodies and long legs. They crawl about over 

 seaweeds and ccelenterates, the juices of which they suck. The 

 Tardigrada, or "bear-animalcules" (Fig. 330), are minute 

 creatures from 0.3 mm. to 1 mm. in length. They live on tree 

 trunks, and in the debris in ditches. The Pentastomida (Fig. 

 331) are parasitic in the noses of flesh-eating vertebrates. 



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