DECAPODA. ANOMURA. 



539 



Tribe 2. PAGURIDEA. 



The great majority of the hermit or soldier crabs and their allies are 

 characterized by the possession of a soft and spirally twisted abdomen, 

 which is protected by a Gasteropod shell or some other covering. With 

 the spiral form of the abdomen is associated a loss of bilateral symmetry 

 (the 2nd-5th appendages of the right, or concave side being aborted) 

 like that which has befallen the Gasteropods whose shells these Crustacea 

 inhabit. The carapace is elongated, becoming membranous behind the 

 cervical groove. The sternal plastra are linear. Antenna 2 with a thorn- 

 like scaphocerite (" acicle "). 1st trunk-legs with large unequal chelae, 

 one (or both) of which acts as an operculum when the animal is withdrawn 

 into its shell. The hindmost pairs short, warted, and, like the uropods, 

 adapted for holding on to the interior of the shell. Gills phyllobranchiae 

 or trichob r a n- 

 chiae. The eggs 

 are hatched as 

 zoaea larvae. 

 After the adult 

 form is reached 

 the shell in 

 which the pos- 

 terior region, is 

 sheltered is, of 

 course, repeat- 

 edly changed to 

 accomm o d a t e 

 the growing 

 body. 



With the 

 typical unsym- 

 metrical h e r - 

 mit-crabs are 

 associated the 

 Pylochelid ae, 

 sym metrical 

 forms which in- 

 habit hollows in 

 stones, worm 

 tubes, sponges, 

 etc., in deep 

 water, the re- 

 markable air-breathing Birgus latro, a Pagurid adapted to terrestrial life, 

 and the Lithodidae which appear to have once acquired and since aban- 

 doned the pagurid habit. 



Fam. 1. Pylochelidae. Abdomen symmetrical, with normal terga. 

 Gills trichobranchiae. Two posterior trunk-legs modified as indicated 

 ^ibove. Deep water. Pylocheles and Mixtopagurus A. M.-E. and Chiro- 

 platea Sp. B. which is blind. Pylocheles Agassizii A. M.-E. was obtained 

 by the Blake at 200 faths. off Barbados, in hollows in agglutinated sand. 

 -P. spinosus Henderson. Challenger. 150 faths. Australia. 



Fain. 2. Paguridae. 2nd antenna with a well developed spine in 

 place of the scale (Fig. 328). 



Sub-fam. 1. Eupagurinae. 3rd maxillipeds separated at their base 3 



FIG. 328. Eupagurus (Pagurus) bernhardus (from Claus, after Cuvier 





