THE GENUS PYLOPAGURUS (CRUSTACEA: ANOMURA) 



IN THE PACIFIC WITH 

 DESCRIPTIONS OF TWO NEW SPECIES 



By 

 Bryce C. Walton 1 



Among the crustaceans popularly known as the "hermit crabs" is the 

 small genus Pylopagurus. Relatively little known from the Pacific, these 

 animals are unique in choosing as a carcinoecium or "dwelling" those 

 structures having an aperture of circular outline and rather uniform size, 

 such as tooth-shells (Dentalium spp.) or the tubes of annelids and 

 mollusks. Adaptation to this means of protecting their soft and un- 

 armored abdomens has been accomplished by the development of a 

 broad, flattened, large pincer which forms a perfectly fitted trap-door, 

 sealing off the entrance when the hermit retreats into his refuge. As a 

 further refinement, at least two species of pylopagurids have developed a 

 unique symbiosis with a colonial hydrocoral, which completely overgrows 

 the gastropod shell except for the aperture, where it is neatly trimmed 

 back by the crab's large pincer. The pylopagurid is thus provided with a 

 "custom-made" aperture which exactly fits the chelate operculum with 

 which it is closed. 



Nine species of Pylopagurus have been described from Pacific waters 

 to date. However, only a small number of specimens have been collected 

 and references to the group have been limited to descriptions of new 

 species and a very few records of collections made. Descriptions available 

 at present are not satisfactory, since they were written at different times 

 by different authors and are not parallel in the diagnostic features used. 

 Furthermore, most of the species have not been illustrated. Consequently, 

 identification is difficult, if not impossible, without access to type material. 



The collections of the Allan Hancock Foundation at the University 

 of Southern California include probably the greatest aggregation of 

 Pacific forms of Pylopagurus available in any one place. These collections 

 from the Eastern Pacific between Oregon and Ecuador, made in the 

 period from 1931 to 1950, are the basis for the present study. Over 500 

 specimens of this genus were examined. The purpose of this paper is to 

 report the knowledge of the geographic and bathymetric distribution of 

 Pylopagurus afforded by these collections, and to facilitate the easy and 

 accurate identification of these hermits. 



1 Captain, MSC, Army Medical Service Graduate School, Washington, D.C. 



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