270 



CRUSTACEANS. 



stoutest, end in simple claws, and are studded with scale-like or spiny tubercles. 



It feeds on the organic matter contained in the mud which it gathers up in its 



nippers, compresses into pellets, and 



transfers to its mouth. The two 



small Crustaceans figured in the 



illustration belong to the family 



Pontoniidce. Both are semiparasitic 



in habits, Pontonia living between 



the valves of mussel shells, and 



Typton being a lodger in sponges. 



The Polycarpinea contains those 



species in which the wrist of the 



second pair of trunk-legs is divided 



into several secondary segments. In 

 1, mussel-prawn (Pontonia tyrrhena) ; 2, sponge-prawn ^ 



(Typton spongkola). (Nat. size.) other respects they are nearly allied 



to the last group. A common British 

 representative is the red shrimp (Pan- 

 dalus montagui), which gives its name 

 to the family Pandalidoe, and is abund- 

 ant upon man}- parts of the British 

 coasts. This tribe is abundantly repre- 

 sented in tropical seas by the hooded 

 shrimps {Alplteidcc), remarkable for the 

 concealment of the eyes beneath the 

 edge of the carapace, and for the 

 enormous size, bright colours, and 

 peculiar shape of the right or left 

 pincers. With this instrument the 

 hooded shrimps, which frequent holes 

 and crevices in the coral-reefs, are able 

 to produce a clicking sound when angry 

 or alarmed by the approach of danger. 

 The last tribe of the suborder, known 

 as Penseidea, appear similar to the 

 Monocarpinea, but may be distinguished 

 by the circumstance that the first three 

 pairs of trunk - limbs are chelate, so 

 that only the posterior two terminate in 

 simple claws. Some of the species of the 

 genus Penceus, belonging to the family 

 Penceidce, attain a large size in tropical 

 seas, and form an important article of 

 commerce. Nearly allied is the little 

 Spongicola venusta, which makes its 

 home in glass-sponges. In this neigh- 

 bourhood may be placed the anomalous 



1 



hooded shrimp, Alpheus (nat. size). 



