
FOOD AND FEEDING 

the three anterior pairs of limbs as foot-claws and the five pairs of posterior 
limbs as walking legs. The eyes are stalked and the gills thoracic. 
Sus-Orper Ampuipopa. ‘This sub-order includes the Water-fleas 
and the marine Sand-hoppers, of which one genus is present in both 
running and standing fresh water. 
Gammarus. Fig.71. This freshwater Crustacean, known as the Water- 
fleaand FairyShrimp,Gammaruspulex,hasa flattened form,the anterior portion 
consisting of the head and thorax covered with a carapace, and the posterior 
portion with six segments and a terminal flap ending 
in a short bristle. The anterior three pairs of legs 
serve for swimming and the posterior legs for swim- 
ming and the hopping motion by which it moves 
more rapidly through the water. The color is a 
translucent dusky grey. It is found in muddy 
streams among half-rotten brush wood and other 
litter, usually hidden under stones or aquatic plants, 
generally feeding at dusk or at night, when it either 

swims leisurely through the water or hops by rapid 
strokes of the posterior legs. Its food is decaying FIG. 71. Gammarus pulex. 
vegetation, small animals and spawn; and will serve aa 
as an effective scavenger in tanks for larger fishes and amphibia but should 
not be introduced with young fishes. 
Sus-OrbeER Isopopa. This sub-order includes the Water-Asel, 
Wood Louse and a number of marine forms. 
AsetLopus. Fig.72. This freshwater Crustacean is known asthe Water- 
Asel, dsellopus tenax, and has a compressed or flattened form and a segmental 
body covered with an olivate armor marked with lighter spots. It reaches 
a length of 1 to 1.5 centimeters, and inhabits still and 
slow-flowing water containing considerable vegetation. 
Its movements are slow and it is usually secreted in 
the mud or on the under side of the leaves of aquatic 
plants; feeding on decaying vegetal substances, smaller 
animals and spawn, and is an active enemy of very 
young fishes. Another more slender and longer-limbed 
form is Asellus communis, a New England States species. 
Sus-OrpeER Decapopa. This sub-order includes 
the freshwater Crayfishes, marine Prawns, Shrimps, 
the true Crabs and Lobsters. These will be treated 
of elsewhere. 

AN ; rr e 
Pie a. Aseliogustanag: The minute Crustaceans are of the greatest, bene- 
Grea yan reed: fit to the growth and survival of the young brood of 
122 
