ON THE LOCOMOTION OF THE MOLLUSCA. 



BY JOSEPH SINEL. 



CONSIDERING the great variety of form assumed by the members 

 of the group Mollusca, one is prepared for a corresponding diver- 

 sity in their modes of locomotion, but perhaps few, Except those who 

 have made the group a special study, have considered how very varied 

 these are, and what different parts of their organization are employed 

 to this end. 



For instance, the general reader may be surprised to hear of snails 

 that jump, and of cockles that can proceed over dry land by bounds 

 of several yards. In fact, so erratic are these animals in their modes 

 of travel, that a general outline of such may not be void of interest. 



Taking first the Lamellibranchs, or Bivalve Molluscs, and confi- 

 ning ourselves in all cases to the adult form, we find that while some 

 are stationary, firmly cemented to rock or stone by one of their valves, 

 e.g. some of the oysters, or moored by a tassel of strong threads (the 

 byssus) after the manner of the common mussel, the majority have 

 the power of slowly trailing themselves, over, or through, the 

 sand or mud by means of the foot, the fresh water mussel affording a 

 familiar example. Others, notably the Pectens, have the power of 

 swimming. This is effected by the smart opening and closing of the 

 shell, and in one member of this family, Lima, this faculty exists to 

 such perfection as to be best described as a graceful undulating flight 

 through the water, each closure of the shell propelling the little 

 animal some eight or ten inches. 



This faculty of swimming, combined with the beauty of the 

 pearly striated shell, and the surpassing gracefulness of the long 

 orange and vermillion fringe of its mantle which forms streamers 

 behind, render this without a doubt the most attractive member of 

 the Mollusca. 



Then, at least one member of the class has very considerable 

 leaping power, this is the marbled cockle, Pectunculus glycymeris. 

 In Jeffrey's British Conchology (Vol. ii., p. 167) it is stated 

 " This animal does not execute a direct progressive locomotion, but 

 only turns the shell round on its disc or from side to side." 



Very different from this has been the experience of the writer 

 who, on several occasions when collecting at night at low tide limit 

 on the great shell gravel reaches of La Rocque point, Jersey — where 

 this mollusc abounds — has been fairly pelted with them as they 



