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Habit and Habitat in the Galatheidea 

 a study in adaptation. 



K. Zimmermann, B.Sc, 



University College of Wales, Ahcryslicyth. 



With Figure 1 and Plates 1-4 in the Text. 



The heterogeneous assembly of Decapod Crustacean types classed as 

 *' Anomura " is well known to present a wide range of variation in 

 structural features ; in fact, the most apparent bond of union between 

 its highly dissimilar sub-groups consists in the still greater disparity 

 which exists between these and members of either " Macrura " or 

 *' Brachyura " proper. The Anomura may best be compared with that 

 other heterogeneous group, the Amphibia : each, apparently of aquatic 

 ancestry, has suffered in the unequal contest with a highly specialized 

 offset from the parent-stock (Brachyura-Eeptilia) ; the survivors of both 

 the ill-fated groups, Anomura and Amphibia, are few in number, varied 

 in type, and probably not closely related among themselves. 



Among the Anomura, the sub-group Galatheidea present a fairly 

 ■connected natural assemblage of types. Study of this sub-group reveals 

 the presence of two distinct and widely divergent lines of specialization — 

 on the one hand, for life on shore (near or above low-tide mark), and, on 

 the other, for life in deeper waters. Thus the group comprises, together 

 with more or less intermediate forms, three well-marked types : 



A. The Galathea sqiiamifera type. 



The characteristic species frequents the fairly open seas which sur- 

 round our coasts, and is rarely found near low-tide mark except for a 

 short time in spring ; the form of body is almost Macrurous, and the 

 abdomen, though usually flexed, is relatively large, and of no little 

 importance in swimming. 



B. The Porcellana platycheles type. 



The characteristic species lives well up in the muddier portion of the 

 intertidal zone, and is common about midway between high and low 



