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ARACHNIDA. MEROSTOMATA 



SUB-CLASS I. MEROSTOMATA 



The Merostomata are aquatic Arachnids which breathe 

 by means of gills borne on the plate-like appendages of 

 the mesosoma. There are two Orders: — (1) Xiphosura, 

 (2) Eurypterida. 



ORDER I. XIPHOSURA 



The only living representative of the Xiphosura is the 

 king-crab, Limulus (figs. 144, 145), found on the eastern 

 shores of North America and Asia, and in the Malay 

 Archipelago and the Indian Ocean. The body of Limulus 

 is covered by a chitinous exoskeleton, and consists of a 



Fig. 144. Limulus polyphemus, Recent. Ventral surface. A, cephalo- 

 thorax or prosoma. B, abdomen. C, portion of the tail-spine. 

 1 — 6, appendages of the prosoma; 1, chelicera; 2, pedipalp ; 3—6, 

 ambulatory legs ; behind the mouth are the small chilaria ; 7 — 12, 

 appendages of the abdomen ; 7, operculum ; 8 — 12, lamellar append- 

 ages bearing gills, m, mouth. Reduced. 



