MARINE BIOLOGICAL STATION AT PORT ERIN. Ill 



The Decapoda or higher Crustacea may be divided 

 into 3 sets : — 



(1) Those that have the tail part or abdomen 



stretched out behind the carapace or shield that 

 covers the head and thorax, as in lobsters, 

 shrimps and prawns (Macrura). 



(2) Those where the abdomen is smaller and is folded 



up underneath the carapace, as in crabs 

 (Brachyura). 



(3) Those where the abdomen is neither completely 



stretched out nor folded up, and is often 

 anomalous in shape, as in hermit crabs 

 (Anomura). 

 Figure XV. shows Macrura, fig. XIX. Brachyura, and 

 fig. XYIII. two interesting kinds of Anomura, which we 

 generally have on view in the Aquarium. No 2 is 

 Galathea squamifera, the " squat-lobster," of which one 

 kind, of a blackish colour, is frequently found under 

 stones at low tide in Port Erin Bay, while another bright 

 red kind is obtained from deeper water by dredging. The 

 abdomen, it will be seen, is partially turned under the 

 body, but can be extended and flapped up and down 

 when swimming. The other figure (1 in fig. XYIII.) shows 

 a " hermit crab " (Ewpagurus prideauxii), with its 

 anomalous abdomen tucked into an old Molluscan spiral 

 shell, on the outside of which is the special kind of sea- 

 anemone Adamsia palliata, mentioned before. These two 

 very unlike animals, the hermit-crab and the sea- 

 anemone, seems to be mutually helpful ; the crab carries 

 about and incidentally feeds the anemone, while the latter 

 by its stinging threads possibly keeps oif fishes and other 

 enemies, and so protects its partner in this strange 

 association. 



The highest of Decapod Crustacea are the Brachyura, 



