CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 11 



are more abundant in deep water. Some are found attached to sea- 

 anemones, upon which they probably prey; others are found climbing 



Fig. 12. A pycnogonid, Nymphon hispidum: c, chelophore; p, 

 palpus; o, ovigerous legs; /, /, /, /, ambulatory legs; ah, abdo- 

 men (After Hoeck). 



over sea-weeds and Hydroids; and sometimes they are dredged in 

 great numbers from deep water. 



They possess a suctorial proboscis. In none of the appendages are 

 the basal segments modified into organs for crushing the prey. 



The cephalothorax comprises almost the entire body; the abdomen 

 being reduced to a mere vestige, without appendages, and with no 

 external indication of segmentation. But the presence of two pairs 

 of abdominal ganglia indicates that originally the abdomen consisted 

 of more than one segment. 



There are typically seven pairs of appendages; but a few forms 

 possess eight pairs ; and in some the first two or three pairs are absent . 

 The appendages, when all are present, consist of a pair of chelophores, 

 each of which when well-developed consists of one or two basal seg- 

 ments and a chelate "hand;" the palpi, which are supposed to be 

 tactile, and which have from five to ten joints when well-developed; 

 the ovigerous legs, which are so-called because in the males they niv 

 used for holding the mass of eggs beneath the body; and the ambula- 

 tory legs, of which there are usually four pairs, but a few forms possess 

 a fifth pair. The ambulatory legs consist each of eight segments and 

 a terminal claw. 



The only organs of special sense that have been found in these 

 animals are the eyes. These are absent or at least very poorly 



