14 Guide to the Mollusca. 



stomachs. .Many fishes feed upon marine Gastropods and 

 Lamellibranchs. Sea-birds feed upon littoral forms between tide- 

 marks and in coastal lagoons and backwaters. Petrels will seize 

 and eat pelagic Cephalopoda. Land-Snails are eaten by numerous 

 birds, notably the Thrush, and also, by mammals such as mice, 

 badgers, and hedgehogs. Crabs, lobsters, beetles, and starfish 

 are among the invertebrate enemies of Mollusca. Young Lamelli- 

 branchs are said to be the exclusive food of the Annelid Magelona. 

 The age to which Mollusca live varies very considerably. 

 Precise figures are available for some Gastropoda and Lamelli- 

 branchia, and of these it appears that the latter may live 

 longer. Certain freshwater Mussels (Anodonta) are said to reach 

 the age of 20-30 years. The Common Oyster may live for 10 

 years. Of Gastropoda, Helix reaches the age of 6 or 7 years, 

 Paludina 8 years, while the Common Periwinkle has lived in 

 captivity for nearly 20 years. The beautiful Nudibranchs do 

 not appear to be so long-lived as other Gastropoda. Sexual 



Fig. 0. 



Helix desertorum. From Woodward's Manual of the Mollusca (by permission 



of Crosby Lock wood & Son). 



maturity in Gastropoda may be attained in the year of birth. 

 The Common Limpet, Patella vidgata, is mature when less than 

 an inch long. After that it continues to grow and sometimes 

 attains a length of over 2J inches. Two-thirds of its final size 

 may therefore be developed after sexual maturity. 



The resistance of Mollusca to adverse conditions is very marked. 

 An Australian Pond-Mussel has been known to live out of water 

 for over a year, and several Land-Snails have revived after a 

 captivity of from two to five years without food. One of the 

 most remarkable instances occurred in the British Museum. 

 A specimen of Helix desertorum, the common Desert Snail of 

 Egypt, was fixed on a tablet in March 1846 and was found to be 

 alive in March 1850, having passed four years in a museum case 

 without any food or moisture. It became torpid in October 1851 

 and was found to be dead in May 1852. Extremes of temperature 

 appear to affect Mollusca less than some other animals. Thus 

 a species of Helix has been said to tolerate a temperature 

 of — 120° C, and Melanopsis parreyssii lives at 42° C. in hot 

 springs in Hungary. 



