COASTLINES 



submerged in water (salt or fresh) while aquatic forms 

 of many kinds cannot survive dry land conditions. Yet 

 the numerous plants and animals between tide-marks 

 survive drastic changes without ill effects. They are 

 deprived of their watery medium as the tide recedes, 

 when they are exposed to the air, the heat of the sun 

 and sometimes fresh water due to the rain. 



The pounding of the waves on the world's sea-shores 

 has affected the general shape of all plants and animals 

 in the intertidal areas. Most of the creatures which live 

 fully exposed to the action of the waves have been flat- 

 tened down from above: crabs, starfish, etc. But there 

 are some which are flattened laterally, such as sand- 

 hoppers : they "lie down" to the sea's merciless blows. 

 Limpets living in sheltered crevices are rounded. Those 

 which live in exposed places are oval and flattened. 



Myriads of creatures resist the sea's tearing and driving 

 percussions by burrowing in the beaches, or clinging 

 tenaciously to rocks — yet there are always a number that 

 get carried away and swirled about in the waters. Shore 

 creatures cling to rocks in all kinds of ways. Most mol- 

 luscs hold on, by suction, by adapting their muscular 

 'Teet" to every microscopical roughness of the rock's 

 surface. But the mollusc evidently finds that this is not 

 enough, for it uses the edge of its shell like a file and works 

 it a little way into the surface of the rock to get a firmer 

 hold. The anemone is unable to supplement its hold 

 with the rasping action, so it presses its body so closely to 

 the rock that its flesh is adapted to every minute indenta- 

 tion over as wide an area as possible. The common 

 barnacle cements itself to the rock with a secretion which 

 securely fixes the box in which it lives to the surface of its 

 dwelling-place. 



Mussels hold on by their beards. Each beard — technic- 

 ally called the ''byssus" — is a cluster of brown threads. 

 Each thread is furnished with a terminal device, some- 

 thing like the ones used by creepers to attach themselves 



129 E 



