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 
other respects they are nearly allied 
to the last group. A common British 
■"WIUCIRI®" 
1, mussel-prawn (Pontonia tyrrhena ); 2, sponge-prawn 
(Typton spongicola). (Nat. size.) 
representative is the red shrimp ( Pan- 
dal its montagui), which gives its name 
to the family Pandalidce, and is abund¬ 
ant upon many parts of the British 
coasts. This tribe is abundantly repre- 
sented in tropical seas by the hooded 
shrimps (. Alplieidce ), 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 Penasidea, 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 
hooded shrimp, Alpheus (nat. size). 
