3236 



THE JOINTED ANIMALS 



\. MUSSEL PRAWN (Piontonia iyrrhena} 2. SPONGE PRAWN 

 (Typton spongicola). 

 (Natural size.) 



forms, and among them the Palcemonidce 

 or prawns. The general form of the 

 body is shown in the figure of the com- 

 mon prawn {Leander serratus). In its 

 native haunts the prawn is nearly in- 

 visible, being almost colorless, translu- 

 cent, and marked merely with streaks 

 of various tints. In the rivers of tropi- 

 cal countries occur prawns (Palcemon) 

 rivaling lobsters in size, and remarkable 

 for the length of their pincers, which 

 may exceed that of the body. Among 

 the largest are P. jamaicensis from the 

 West Indies and Central America, and 

 the Indian P. lar, so much esteemed 

 when cooked as a curry. Also belong- 

 ing to the same section is the family 

 Atyidce, containing a few genera such as 

 Atya and Caridina, found in both East- 

 ern and Western Hemispheres in fresh- 

 water streams and lakes. In Atya the 

 trunk limbs are curiously constructed, 

 the first two pairs being short and sub- 

 equal with the two fingers of the pincers 

 tipped with a long tuft of hairs. The 

 remaining three pairs, of which the first 

 is much the stoutest, end in simple 

 claws, and are studded with scale-like 

 or spiny tubercles. It feeds on the or- 

 ganic matter contained in the mud 

 which it gathers up in its nippers, corn- 



rostrum and no spines on the carapace; 

 but some of the other members of the 

 family have crests of spines on the 

 carapace, and sometimes a largish 

 rostrum as in the Arctic Sderocrangon 

 boreas. In Rhynchocinetes typus from 

 the South Pacific, this rostrum is not 

 only large but movably jointed to the 

 carapace. The section Monocarpinea 

 differs from the last in having the 

 first and second trunk limbs completely 

 chelate, and the second pair larger 

 than the first. To this section be- 

 long a number of fresh and salt-water 



HOODED SHRIMP, Alpheus. 

 (Natural size.) 



