THE CLASS CRUSTACEA 321 



species should be regarded with suspicion in thickly 

 populated areas, and the land-crabs should be avoided 

 altogether as food. 



The other Malacostraca can merely be mentioned, order by order. 

 None are used as food, though some— and their larvK— are of economic 

 importance as contributing to the sustenance of fishes. Some of those 

 Isopoda that are parasitic on fishes and prawns may come under the 

 notice of the medical officer. 



Order Leptostraca. 



The Leptostraca, or Nebaliacea, are small marine Crustacea, only 

 one species — living in the great depths of the sea — exceeding half an inch 

 in length. The tail ends in a caudal fork like that of most Entomostraca, 

 and the anterior half of the body is enclosed in a bivalve shell like that of 

 the Ostracods and certain Phyllopods — only transparent. The eight pairs 

 of thoracic appendages are all alike, and are commonly leaf-like, some- 

 what resembling those of the Phyllopods. The Nebaliacea differ from 

 all other Malacostraca in having 8 abdominal segments and a long 

 caudal fork. 



Order Syncarida. 



This order includes two living species, both of small size, of which one 

 is found in mountain pools in Tasmania, and the other in fresh-water 

 pools in South-eastern Australia. They resemble small Amphipoda (see 

 below), the body being elongate and not having a carapace, and all the 

 segments behind the head being distinct from one another ; but they 

 differ conspicuously from Amphipods in having biramous, thoracic legs. 



Order SCHIZOPODA. 



A few members of this order are found in fresh water, but the 

 majority are marine, living at or near the surface of the ocean. Most 

 are quite small, but a comparatively gigantic species from the deep sea 

 attains a length of 6 inches. The Schizopods much resemble small and 

 delicate prawns, from which they are distinguished by the form of the 

 thoracic appendages, all of which, generally, are feathery, biramous 

 swimming-feet with gill-plumes (when present) freely projecting from 

 them. 



Order Cumacea. 



These are small or minute Crustacea found only on the sea-bottom. 

 They can usually be recognised by their large swollen cephalothorax, the 

 anterior part of which is enclosed in a carapace, by their long and very 

 slender abdomen, and by their strong cuticle. 



