A3IPHIP0DA 365 



sile; the eggs are carried on the ventral surface of the thorax in a 

 brood pouch formed by flat projections of the thoracic legs and the 

 young animals are like the parents in form, there being no metamor- 

 phosis: 2 orders. 



Key to the orders of Arthrostraca : 

 a^ Usually laterally compressed; very often jumping animals. . . .1. Amphipoda 

 Ca Usually dorsoventrally flattened ; many terrestrial and many parasitic. 



2. ISOPODA 



Order 1. AMPHIPODA.* 



Body elongated and usually laterally compressed; first 2 pairs of 

 periopods, which are called gnathopods (Fig. 577, 3 and 4), usuallj' 

 larger than the others and subchelate, being used for grasping the food ; 

 gills on the periopods; hinder 3 pairs of pleopods usually adapted for 

 jumping: about 45 families and 2,300 species, which are almost exclu- 

 sively marine, many species dwelling on the seabeach, buiTowing in the 

 sand or living under stones or decaying vegetation; food consisting 

 mostly of living or dead animals of all kinds, also of decaying vegetable 

 matter; a number of species are parasitic; 3 suborders. 



Key to the suborders of Amphipoda : 



Oi Seven free thoracic segments. 



hi Head very large, with very large eyes 1. Hyperiidea 



5, Head and eyes not of unusual size 2. Gammaridea 



Oj Six free thoracic segments ; abdomen very rudimentary 3. Caprellidea 



Suborder 1. HYPERIIDEA. 



Head and eyes both very large; maxilliped without a palp; 7 pairs 

 of thoracic legs present: parasitic or living on or in pelagic animals, 

 especially medusae; 4 families. 



Key to the families of Hyperiidea here described: 



Oi Usually found in medusae 1- Hyperiidae 



02 In the tests of Salpa or Pyrosoma 2. Phronimidae 



Family 1. HYPEKIIDAE. 



Head large and almost entirely occupied by the enormous eyes; 

 5 abdominal segments ; mandibular palp present : usually found in large 

 medusae; about 8 genera. 



Hypeeia Latreille. Gnathopods feeble: several species in Aurelia, 

 Cyanea, and other medusae; 2 species on the Atlantic coast. 



H. galba (Montagu). Periopods with-«very few setae; length 15 



mm. : in Aurelia; coast of New England. 



* See "Synopsis of the Amphipoda," by S. J. Holmes, Am. Nat, Vol. 37, p. 267, 

 1903. "The Amphipoda 1. Gammaridea," by T. R. R. Stebbing, Das Tierreieh, 1900. 

 "Tlie Amphipods of Southern New England," by S. J. Holmes, Bull, of U. S. Fish. Com., 

 Vol. 24, p. 457, 1904. "The Freshwater Amphipoda of North America," by Ada L. 

 Weckel, Proc. U. S. Nat. Mus., Vol. 32, p. 25, 1907, 



