< ^L._Tf"r 



The sowbiig Oniscus is about % inch long. Like other 

 sowbugs it is a terrestrial isopod common under bark 

 of fallen trees, or logs, or stones. (Hugh Spencer) 



The pill bug Armadillidiitm is one of the terrestrial 

 isopods that are ready at a moment's notice to roll up 

 into a compact ball. { Switzerland. Otto Croy ) 



i 



mysids there at night, seeing them from a skiff as little 

 darting constellations of bright lights. Marine mysids 

 carry their light-producing organs with them, but the 

 few representatives of this order in the Caspian Sea 

 and in large lakes of Europe and North America 

 follow a different rule applying to all crustaceans in 

 fresh water; they lack luminous organs. 



EUPHA USIDS 



Krill, the principal food of whalebone whales, are 

 pelagic crustaceans of the order Euphausiacea. Their 

 appearance is even more shrimplike than that of 

 mysids, for the euphausid carapace is fully developed, 

 shielding the bases of all of the swimming legs. Eu- 

 phausids carry their eggs below the slender abdomen. 

 Most members of this order are a brilliant red, and 

 when numerous they color the ocean's surface until 

 whalers refer to it as "tomato soup." Wherever this 

 color is widespread, whalebone whales can be ex- 

 pected. 



At night euphausids may be equally noticeable be- 

 cause of their bright luminescence. When a ship 

 disturbs them, they glow for minutes at a time, mak- 

 ing the waves visible far astern. The underside of the 

 first four abdominal segments bear light-producing 

 organs. Usually another pair are located on the outer 

 surface of the eyestalks, where they shine like electric 

 torches into the water close to the mouth. The com- 

 pound eyes have components facing in this direction 

 too, and it seems likely that the animal actually jack- 

 lights its food (copepods) at night. In many euphau- 

 sids the compound eyes are strongly bilobed, one 

 portion seemingly directed upward and perhaps used 

 to identify the abdominal lights of other krill. The 

 other portion faces forward and downward, appar- 

 ently for use in feeding. 



LONG-TAILED DECAPODS 



True shrimps, along with lobsters, crayfishes, and 

 crabs, all belong to the order Decapoda. As the name 

 suggests, all of them have ten thoracic legs. These 

 include the large pincer-tipped appendages of North 

 Atlantic lobsters as well as the smaller legs used in 

 walking over the bottom. A number of pairs of ap- 

 pendages are associated with the mouth as food- 

 handling organs, and still additional pairs below the 

 abdomen serve in holding the eggs until they hatch. 



Shrimps and prawns are free-swimming decapods, 

 usually with a compressed body (Plates 90, 92). 

 Peneiis setiferiis is the most important commercial 

 shrimp of American Gulf Coast waters, with about 

 100,000 tons taken annually. In Europe its place is 

 taken by Crago septemspinosiis (also known as 

 Cningon vulgaris), a denizen of sand flats and tide 

 pools on both sides of the North Atlantic. On the 

 American west coast the commercial shrimp is Crago 

 framiscoriim. 



