CHAPTER XXV 

 HIGHER CRUSTACEANS (MALACOSTRACA) 



By a. E. ORTMANN 

 Curator of Invertebrate Zoology, Carnegie Museum, Pittsburgh. 



To the higher Crustaceans (subclass Malacostraca) belong such 

 forms as the sow-bugs, scuds, shrimps, prawns, crayfishes or craw- 

 fishes, and crabs. These popular names are not sharply defined, but 

 it appears convenient to restrict the name sow-bugs to the Isopods, 

 that of the scuds to the Amphipods. For the Mysidacea, the term 

 opossum-shrimps has been introduced, while the names shrimps and 

 prawns belong to certain Decapods, and are almost synonyms : the 

 former is now used chiefly for the smaller forms, the latter for 

 the larger ones. Crayfishes and Crawfishes are the Decapods of the 

 genera Cambarus and Potamohius. Often for these also the name 

 crabs is used, but this is a misnomer, and it should be restricted to 

 marine forms of the type of the common edible blue crab. 



The great majority of the Malacostraca belong to the sea, 

 occurring in all regions, near the shore as well as on the bottom 

 of the deep sea, and floating and swimming on the surface. But a 

 considerable number have entered the fresh water, and are found 

 in rivers, creeks, ponds, lakes, etc. A few forms are known, 

 which live parasitic upon other aquatic creatures. 



They are omnivorous, feeding on vegetable and animal matter, 

 both living and dead, but dead and decaying matter is preferred 

 by most of them. Asellus (of the Isopods) distinctly prefers de- 

 caying vegetable matter, whUe Palaemonias (of the Decapods) 

 seems to be specialized as a mud-eater: at any rate, the peculiar 

 hair-tufts on the claws probably serve the same purpose as in the 

 allied tropical forms, where it has been observed that they are 

 used in gathering mud, like a small brush. 



Generally, the fresh-water Malacostraca are not very conspicu- 

 ous, some because they are rather small and easily escape detec- 

 tion, while others, which are larger, keep in hiding, under stones 



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