MARINE CRUSTACEANS 167 



or operculum of the shell, sweeping them to and fro like a net, and thus bring- 

 ing the minute animals on which they feed to their mouths. 



Another well-known barnacle is the Goose Barnacle (Lepas anatifera), 

 frequently found attached to the wooden bottoms of ships which are brought 

 into dock to be " scraped " that is, to be cleaned from the thousands of 

 barnacles which have fixed themselves there. They attach themselves head 

 downwards upon a kind of stalk (peduncle), really consisting of the pillar of 

 cement with which the little animal covered its feelers before it changed into 

 its final form. There are many other kinds, some found attached deeply 

 to whales most uncomfortable parasites ! 



2. The Brine Shrimp (Artemia salina) is a reddish animal about half an inch 

 long, with eleven pairs of legs and a long, jointed tail. It is to be found in 

 every salt lake, as well as on the shore. 



3. The Sand-hopper (Talistra locusta) may be found in hundreds by turning 

 over any bunch of seaweed on the shore, or burrowing in moist sand. Its 

 three pairs of hind-legs have joints that bend forward, while those of the 

 front legs bend backward. It breathes by means of gills, and feeds upon 

 decaying seaweed and other matter, being the most useful scavenger of the 

 sea-edge. It is the prey of all the shore birds and of crabs, and at least one 

 beetle tunnels after it in the sand, and devours it in its burrow ! 



4. The Sand-screw is closely allied to the Sand-hopper ; but whilst the above 

 sinks its burrows almost vertically in the sand, the Sand-screw drives them 

 horizontally just below the surface, and, instead of jumping like the Sand- 

 hopper, it screws itself along on its side. 



5. The Shrimp (Crangon vulgar is) is so familiar as to need no description. 

 It is so transparent as to be almost invisible in the water, and when resting 

 at the bottom its speckled body looks almost exactly like the sand. As if 

 this were not sufficient protection, it can bury itself in the sand, rapidly scooping 

 a furrow with its hind-limbs, sinking into it, and then covering itself with sand 

 by means of its feelers. The female carries her eggs on her swimming feet, 

 and as she is found thus laden at all seasons, there appears to be no special 

 breeding time. 



6. The Great Prawn (Leander serratus) is a bold and fearless animal in its 

 native element, and a handsome creature when examined in detail. Note the 

 pear-shaped eyes, the antennae, two pairs of " hands " (chela), and three pairs 

 of walking feet. Behind these are five pairs of swimming organs, or legs, and a 

 four-plated, fan-shaped tail, by means of which the prawn can leap backwards 

 with astonishing speed. Both prawns and shrimps feed on carrion. There 

 are several species of both these animals (the JEsop Prawn, for example, to be 

 found in summer in the rock pools, distinguished by the hump on its back). 

 Many small prawns are sold as shrimps, but there is one striking difference 

 easy to observe the long beak or spike projecting from the edge of the shield, 

 or carapace, which covers the back is set with sharp teeth, like a saw, in the 

 prawn, whilst in the shrimp it is perfectly smooth. 



