SCAPHOPODA 97 



forth, in a revolving manner, in boring. Each valve has an apophy- 

 sis; a long, riblike process, to which the muscles of the foot are at- 

 tached. The two pallets, which are placed in the posterior end of the 

 animal, are flat, with a stout, rounded stalk, ending in a slight 

 calcified knob. 



Class SCAPHOPODA 



This is the smallest class of the Mollusca. The anatomical 

 structure of its members differs so widely from that of other mem- 

 bers of the phylum that it was not until 1819 that scaphopods were 

 established as mollusks and separated from those marine worms 

 which secrete calcareous tubes. Scaphopods show definite relation- 

 ship to gasteropods in the possession of a univalve shell and a radula, 

 and to the pelecypods in similarity of the foot and lack of a distinct 

 head. The animals are eyeless, nonoperculate, carnivorous, and uni- 

 sexual. They are found in all but polar seas, and their bathymetric 

 range is from less than one fathom to abyssal depths. 



The name Scaphopoda, derived from the Greek scapha, boat; 

 fod, foot, is descriptive of the pointed burrowing extremity belong- 

 ing to mollusks of this class. The shape of the foot suggests a vessel's 

 sharp prow or ploughshare, and differences in the development of 

 its tip present important family characters. Small carnivorous mol- 

 lusks are their worst enemies, and shells are frequently found which 

 have been bored near the apex. 



The shells are tubular, nonspiral, open at both ends, and gen- 

 erally tapered toward the posterior end. All growth takes place at 

 the anterior — larger — end, and the posterior extremity is truncated 

 as growth proceeds at the opposite end. The size of the shells varies 

 from two or three to one hundred seventy-five millimeters. This type 

 of shell is characteristic of the group and is found nowhere else 

 among the Mollusca. 



Scaphopod shells have been used as ornaments and as charms 

 against the evil eye, and among the Indian tribes of Northwest 

 America, strings of the perfect shells of a Pacific species of Den- 

 talium represented the gold standard until superseded by the more 

 practical advantage of the Hudson's Bay Company's blankets. 



