MOLLUSCS IOI 



whole or piecemeal. An Oyster reaches edible size in 

 about four years. 



Early travellers often brought back wonderful stories 

 of oysters growing upon trees, and this observation has 

 proved not so impossible as might at first appear. In 

 tropic seas mangrove roots and overhanging branches 

 which are submerged at high water often acquire a dense 

 covering of oysters, which, when the tide retires, may be 

 left many feet above water level, smothering the trees 

 with dense layers of their shells. 



Nearly related, though bearing little superficial resem- 

 blance to the Oysters, are the Fan Mussels (Pinna). These 

 shells are acutely triangular and of thin horny texture 

 and may reach several feet in length. They are remarkable 

 for the profuse and silky nature of the anchor-threads, 

 which have been employed in the weaving of various 

 small articles of clothing. Pinna, as well as the Oyster, 

 are often hosts of the Pea Crab. 



The Cockles (Cardium), like the Oyster, have a world- 

 wide distribution and may at once be recognized by their 

 globular form and strange ribbed shells. The animal has 

 a very strong muscular foot several inches in length and 

 with it can perform surprising leaps, often covering several 

 yards at a bound. Cockles are essentially sand burrowers, 

 their syphons reaching up to the pure water when 

 submerged. 



In a number of allied families popularly known by the 

 all-embracing title of " Clams," the syphons may reach a 

 prodigious length and are often united in a leathery 

 protective covering. The true Clams are massively 

 shelled molluscs of tropic and semi-tropic seas, where they 



