WAVE-OUREENTS ON SHALLOW-SEA EAUNAS. 265 



The marine fauna exposed to the action of waves may be con- 

 veniently divided into two groups of animals, viz. those that live 

 on the tidal strand, and those that live in, or on, the sea-bottom 

 outside tide-marks. 



(1) Animals Living on the Tidal Strand. 



These may be further considered under the following heads, 

 viz. : — 



{a) Animals living on rock or other firm foundation ; and 



(b) Animals living in sand or other incoherent deposit. 



(«) Animals living on a Firm Foundation. — The methods by 

 which animals living on, or in, rocks resist the attacks of waves 

 are so well known that they need not occupy our attention. 

 Suffice it to say that among them are included great powers of 

 permanent attachment, as evidenced by the oyster and mussel ; 

 of temporary attachment, as evidenced by the limpet and sea- 

 anemone ; and of boring, as evidenced by the pholas and other 

 rock-boring mollusks. 



(Z>) Animals living in Sand. — The habitat being unstable under 

 the attacks of waves and currents, no powers of attachment will 

 serve the inhabitant. Safety lies in the celerity with which the 

 animal can penetrate the sand, either to avoid being washed away 

 in the denudation of the deposit, or to force its way to the sur- 

 face through any accumulation that may be piled over it. We 

 have a good example in the case of Solen vagina, one of the most 

 active of mollusks in penetrating the sand in which it lives. 

 Describing the genus, Dr. Gwyn Jeffreys observes : — " When the 



Solen is disturbed it rapidly disappears below 



the surface to a depth of two or three feet " (Brit. Conch, 

 vol. iii. p. 13). 



(2) Animals living at the Sea-hottom oidside Tide-marJcs. 



The case of a rocky bottom needs no consideration, as the pro- 

 tection afforded is as great as on the tidal strand, whereas 

 the wave-currents are weaker. There remains to consider the 

 case of 



(e) Animals that live in a sandy or muddy bottom, or have the 

 power of burrowing into it ; and (d) that of animals which live 

 on the surface of the bottom. 



(c) Animals that live in a sandy or muddy hottom outside 



