THE DIATOM CELL WALL 

 The diatom cell wall (frustule) is made of silica and consists of two 

 overlapping halves, each composed of a more or less flat surface, the 

 valve, to which are joined one or more hoop-like bands, the girdle and 

 intercalary bands (see below). 



r 



-\ 



LI 



^ 



/ 



> 



j 



vm 

 ib 

 gb 



Girdle view of frustule showing valves, v; intercalary bands, 

 ib ; girdle band, gb; girdle, g; and valve mantle, vm. 



The valves of the centric diatoms are generally circular in outline, with 

 their markings arranged symmetrically about a central point; whereas, the 

 valves of the pennate diatoms are generally elongate (linear) with their 

 markings arranged in transverse rows along each margin. 



Pennate Centric 



Valve views of pennate and centric diatoms showing the central 

 area, a; raphe, r which usually occupies the medial axis of 

 the valve; striae, s; and costae, c. 



