90 THE BIOLOGY OF THE SEA-SHORE 



connection it is interesting to notice that in forms like brittle 

 stars which have no delicate ectoderm to protect and which 

 practise autotomy in addition, pedicellariae are either 

 completely absent or at most rudimentary. 



The higher Crustacea are also, through the nature of 

 their covering, very liable to become encrusted with sedentary 

 forms, especially barnacles. In the University Museum, 

 Aberdeen, is a crab of comparatively small size with its 

 carapace literally loaded with a heterogeneous collection of 

 Lamellibranchs {Ostnea, Anomia), Gasteropods, barnacles, 

 tubeworms, polyzoa and hydrozoa of various kinds, etc. 

 This assemblage of forms, far exceeding the actual crab in 

 bulk, has evidently grown through each new-comer affording 

 a fresh area of foothold. The crab serves as nucleus for 

 an ever-growing colony. In view of such facts the act of 

 moulting assumes a double significance, for not only does 

 the shedding of the cuticle permit the animal to grow, but 

 it is of immense advantage in liberating it from an embarrass- 

 ing collection of sedentary forms. 



Herdman (1907) remarks on the term " granny crab " 

 employed by Port Erin fishermen to denote a crab of any 

 size above four inches which is of worn and dilapidated 

 appearance. The shell of these " granny crabs " is pitted 

 and stained with black and the great claws are corroded and 

 often broken. The surface is frequently overgrown with 

 barnacles and other foreign bodies. Such crabs are caught 

 in considerable numbers during July and August and are 

 promptly killed by the men, who are under the impression 

 that they are diseased. When eaten, the flesh is said to 

 have a strong, bitter taste, and powerful purgative effect. 

 Herdman states, however, that there is in all probability 

 nothing abnormal about these crabs. They are merely 

 individuals which are nearing the time when in every second 

 year the crab will cast its shell. The practice of destroying 

 them is consequently unwarranted. 



The shells of molluscs, particularly those of sessile 

 bivalves, are likewise subject to encrustation. The menace 

 here is not so much from unrelated species as from young 



