296 LIVING THINGS IN THEIR ENVIRONMENT 



flats are the permanent homes of many mollusks, little 

 periwinkles, and other snails almost covering the surface 

 in places. Other larger snails, whelks, are found, as well 

 as many bivalve or two-shelled mollusks. Some of these, 

 like the scallops, not permanent residents, live on the sur- 

 face of the sand or mud ; others, like mussels and oysters, 

 are attached to the rocks ; while still others, like the clams, 

 burrow into the sand by means of a muscular foot. Some 

 clams have long tube-like siphons which project out to 

 the surface. Through the siphon the animal gets oxygen 

 and water containing microscopic food. (See page 295.) 

 Many little green or brown crabs will be found, as well as 

 the funny little hermit crabs carrying around snail shells 

 in which they have made their homes. 



Life in the Sand or Mud. The sand or mud is honey- 

 combed with burrows of several different kinds of worms. 

 One of the most common is the sandworm, which has a 

 jointed body, each joint provided with flat appendages 

 strengthened with many bristles and a head provided 

 with horny jaws, tentacles, and four eyes. Other seg- 

 mented (jointed) worms may be found, as well as some 

 unsegmented species. Small crustaceans and burrow- 

 ing crabs are often seen digging into the sand at our ap- 

 proach, while sea cucumbers and sea urchins, both " spiny 

 skinned " animals, are sometimes found on the surface of 

 the sand. 



Life on the Rocks. Along a rocky shore quite a dif- 

 ferent association of animals is found. Here we will find 

 great densely-packed communities of barnacles, a fixed 

 crustacean, easily distinguished by its white shell divided 

 into plates ; while mussels of several species are numerous, 

 half covered by masses of brown fucus or other seaweeds. 

 Often we find starfish or sea urchins, while sheltered under 

 rocks and in pools are the wonderful sea anemones. These 

 animals belong to the same group as the corals. When 



