140 THE FAUNA OF THE DEEP SEA 



naturalists considered to be related to the Crustacea 

 and by others to the scorpions and spiders. 



Like the Brachiopoda the Pycnogonida are not 

 usually found in greater depths than 500 fathoms. 

 Out of the twenty- seven known genera, only five 

 extend into the abyss, and not one of these can be 

 called a true deep-sea genus. 



There are three genera, Nymj^hon, Collosendeis, 

 and PhoxicJiilidium, that show a very wide distribu- 

 tion over the floor of the ocean, and are capable of 

 existing at the greatest depths, and of these the 

 species of the genus Nymphon have a truly remark- 

 able range extending from the shore to a depth of 

 2,225 fathoms. 



' As a rule,' says Hoek, ' the deep-sea species are 

 slender, the legs very long and brittle, and the sur- 

 face of the body smooth.' They have further, either 

 no eyes at all or rudimentary eyes without pigment, 

 and in many cases — as, for example, Collosendeis — 

 they are distinguished for reaching to a gigantic size 

 compared with their shallow-water relatives. 



The Tunicata is the group of animals that 

 includes all those curious vegetable-like organisms 

 found upon our coasts that are familiarly known as 

 sea -squirts, or Ascidians, besides the salps, pyrosomas, 



