458 ARACHNIDA 



indicate that they are the most primitive of all arthropods. The order 

 contains about 6 genera and 50 species. 



1. MACROBIOTTJS S. Schultze. Claws all or in part double and often 

 of different lengths; dark but never red pigment in the integument; no 

 feelers or cirri on head; a pair of strong teeth in the 

 mouth: 7 species. 



M. hufelandi Schul. (Fig. 718). Each leg ends 

 with 2 double claws, the 2 sides of each pair being 

 firmly fused and one of them with a small branch 

 claw; length .7 mm.: common in fresh-water ponds. 



2. ECHINISCUS S. Schultze. Claws all single and 

 not double, several being on a leg, all of the same 

 length; 2 red eyes present, also short cirri or feelers 

 beside the mouth on each side; 2 long teeth in the 

 mouth; the cuticula, jointed on the back, often has red 

 spots in it, and usually spines or hairs project from it : 

 about 13 species in both fresh and salt water. 

 E. sigismundi Schul. Third leg with a short spur; each leg ends 

 with about 8 claws; 2 sharp palps on each side beside the mouth, and 2 

 more beside the eye ; length .2 mm. : marine, among algae. 



E. testudo Doyere. Body reddish in color and opaque; length .3 

 mm.: often in the moss of damp roofs. 



ORDER 11. PYCNOGONIDA.* (PANTOPODA.) 



Sea spiders. Marine arachnids, usually of small size, in which the 

 body consists of a large segmented cephalothorax and a minute rudimen- 

 tary abdomen (Fig. 719). Seven pairs of appendages are present, of 

 which the hinder four pairs are the very long, 9-jointed legs, which seem 

 to have developed at the expense of the trunk, as it is reduced to the 

 smallest proportions. The three forward pairs of appendages are the 

 long chelate mandibles, the slender pedipalps, and the slender ovigerous 

 legs, which are wanting in the females of certain species. The cephalo- 

 thorax is made up of the following five segments: the anterior more or 

 less cylindrical rostrum, at the front end of which is the mouth; a large 

 segment bearing the mandibles, the pedipalps, the ovigerous legs and the 

 first pair of walking legs, as well as 4 eyes ; and 3 segments, each bearing 

 a pair of legs. The digestive tract is complex in structure, long diver- 



* See "The Pycnogonida of New England and Adjacent Waters," by E. B. Wilson, 

 Rep. TJ. S. Fish. Com. for 1878, p. 463, 1880. "A Contribution to the Embryology 

 and Phylogeny of the Pycnogonids," by T. H. Morgan, Studies Biol. Lab., Johns Hop. 

 Univ., Vol. 5, 1890. "Notes on the Habits of Pycnogonids," by L. J. Cole, Biol. 

 Bull., Vol. 2, p. 195, 1901. "Pycnogonida," by D. W. Thompson, Camb. Nat. Hist., 

 Vol. 4, p. 500, 1909. 



