flea-shaped or shrimplike. Fresh-water scuds with 

 this form include the '/i-inch Gammarus and Hya- 

 lella, both acrobats of no mean ability. Their reper- 

 toire includes swimming or climbing submerged vege- 

 tation by using the legs on the thorax, and leaps 

 produced with the aid of longer appendages on the 

 abdomen. Most of the world's seacoasts have species 

 of Gammarus, which feed on both living and dead 

 vegetation. All scuds provide fish with important 

 food. 



The conspicuous amphipods on sandy beaches are 

 the '/2-inch beach fleas, such as Orchestia agilis and 

 Talorc/iestia longicornis. These creatures hide in 

 vertical burrows in the wet sand or among piles of 

 seaweed, where they can remain in humid surround- 

 ings or explore for food. If the seaweed is disturbed 

 the beach fleas display the bouncing leaps for which 

 they have been named. 



The order Amphipoda includes some astonishing 

 animals as well. One of them is Caprella, the '/i-inch 

 skeleton shrimp, whose body is a series of elongated 

 cylindrical segments bearing two pairs of slender, 

 hook-ended legs near the head and three more pairs 

 at the rear. With these appendages the skeleton 

 shrimp clings to seaweeds, hydroids, corals, and 

 wharf pilings. It moves in slow motion with the gait 

 of a measuring worm while stalking animals it can 

 snatch with its anterior appendages. Some skeleton 

 shrimps are grayish and translucent, others cream- 

 colored or reddish. 



Another strange amphipod is Parucyamiis. the 

 whale louse, which resembles the skeleton shrimp in 

 size and body parts, but which is broader, more flat- 

 tened, and constricted between segments. Its legs are 

 more powerful grasping organs than those of Cap- 

 rella. Whale lice creep in large numbers over the sur- 

 face of huge whales, hooking their legs into the skin. 

 They grasp a firm hold while gnawing out pits in 

 which the body of the amphipod is protected from 

 water rushing past the swimming whale. The entire 

 nourishment of a whale louse is taken at the whale's 

 expense. 



Still another member of order Amphipoda is the 

 glassily transparent Phronima sedentaria, whose 

 head is so elongate as to suggest that of a horse. It is 

 occupied almost entirely by the compound eyes. 

 Inch-long Phronima captures one of the equally 

 transparent colonies of the tunicate Salpa (p. 288) 

 and takes up residence in the hollow, barrel-shaped 

 tunic. It is carried along by the salp colony, and feeds 

 on the larger animal particles entering the colony's 

 central cavity. Phronima even uses this adopted 

 home as a brood chamber for her own young. 



Crustaceans more than an inch long tend to be 

 more familiar to us, and to be valued either as human 

 food or as nourishment important to large fish in 



Rocks are often almost coated by the shells of acorn 

 barnacles (Balaniis). The two pieces of the shell that 

 close the cavity can be drawn apart to let the bar- 

 nacle use its feet to kick food into the mouth. ( Eng- 

 land. Ralph Buchsbaum ) 



which man is interested. A majority of these crus- 

 taceans have at least a superficial similarity to 

 shrimps and lobsters. Their paired compound eyes 

 are on movable stalks, and at least the first few seg- 

 ments of the leg-bearing thorax are fused together 

 with the head to form a cephalothorax with shield- 

 like top and sides (a carapace). This lends some 

 rigidity to the fore part of the body, and often corre- 

 sponds to use of the tail fin as a scoop in swimming 

 backward, as is so characteristic of lobsters and cray- 

 fishes. 



OPOSSUM SHRIMPS 



Among members of the order Mysidacea the 

 carapace does not extend far enough backward to 

 cover all of the leg-bearing segments. Mysids are al- 

 most entirely pelagic, and their legs are all forked 

 paddles suited for swimming but not for walking. 

 These creatures are called "opossum shrimps" be- 

 cause the female carries her eggs beneath her thorax 

 in a pouch formed of special plates. The young 

 usually hatch in the nauplius stage and transform into 

 the shrimplike adult form. 



Mysis stenolepis is one of the most important 

 mysids to man, for it is a major item of diet for such 

 commercial fishes as shad and flounder. They find 

 the mysid in abundance near shore, often among 

 tangles of eelgrass. Sometimes a person can detect 



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