262 CRUSTACEANS 



not upon the breast-plate of the cephalothorax. Moreover, as in the Dortppidce of 

 the preceding tribe, the last or last two pairs of legs are shorter that the rest, and 

 dorsally placed, as shown in the illustration of the common Dromia vulgaris. 

 The crab uses these limbs to hold foreign bodies like sponges and shells beneath 

 which it thus lies concealed. 



LONG-TAILED GROUP, Suborder Macrura. 



This suborder, comprising the lobsters, hermit-crabs, prawns, and shrimps, is 

 distinguished by having the abdomen or tail usually of large size, and constituting 

 a powerful flapper for swimming, in which function it is assisted by the 

 enlargement of the appendages of its last segment to form with the telson a 

 powerful tail-fin. The external maxillipedes are slender and leg-like, and the 

 antennae usually longer than the body. The first tribe, Anomura, contains forms 

 which typically have a symmetrical tail. With these were originally classified the 

 anomalous crabs, and there is no doubt that some of the species bear a striking 

 resemblance to the latter. This is shown in the illustration of the broad-clawed 



porcelain -crab (Porcellana platycheles), which frequents 

 rocks and seaweed at low water. It may be distinguished 

 from the true crabs by its long antennas, the presence 

 of a tail-fin, and the slender unflattened external maxil- 

 lipedes. The most familiar members are the hermit- 

 crabs, which abound in all seas, and are represented by 

 several British species. In the typical forms, the integu- 

 ment of the abdomen is soft; and, aware of its defenceless- 



BKOAD-CLAWED PORCELAIN . i i i 



CRAB (nat. size). ness, the hermit-crab invariably thrusts itself for protection 



into some empty shell, which it subsequently never 



willingly quits, save for the purpose of changing its abode for a larger one, when 

 compelled by the exigencies of growth. It is not an uncommon thing to find shells 

 containing a hermit-crab surmounted by a large anemone. The advantage to the 

 crab of this association is considerable, for anemones are so distasteful that no fish 

 will bite at them twice, and consequently a fish that would, under ordinary circum- 

 stances, greedily swallow a hermit-crab, shell and all, w T ill not so much as sniff at it if 

 protected by an anemone. One of the commonest deep-water British hermit-crabs, 

 Eupagurus prideauxi, is invariably found associated with an anemone, but the 

 latter adheres to the lower surface of the shell in such a manner that its mouth 

 and tentacles are situated immediately below the forepart of the crab's body. It 

 is thus able to share in the meals that the crab procures for itself, and the com- 

 panionship is consequently mutually beneficial to the two. An advantage conferred 

 upon the crab by the presence of the anemone results from the fact that the latter 

 gradually absorbs the shell in which the former is lodged, so that there is no 

 occasion for it to change its abode with growth, the soft tissues of the polyp 

 offering no resistance to the crab's increase in size. Certain hermit-crabs have 

 forsaken the sea as a permanent abode, and spend the greater part of their lives on 

 land. For instance, the genus Cenobita, which occurs both in the West Indies and 

 India, may be met with in forests far from the coast. The best known of these 



