Introduction to Freshwater Algae - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 37

aa

vp

v

e

j
g

e

pa

vp v p

r

g

(A) (B)

h v

h

r

t a

p a p a

ta

cn

v v

r

g g

p n

aa

vp

15 μm

Figure 1.13 Details of frustule structure in a pennate diatom ( Pinnularia ). Top: Diagrams of cell wall structure, with
principal axes. Top left: Valve view. aa, apical axis; ta, transapical axis; pn, polar nodule; r, raphe. Top middle: Girdle
view. pa, pervalvular axis; vp, valvar plane; h, hypotheca; e, epitheca; g, girdle. Top right: Transverse section. Fritsch,
1956. Reproduced with permission from CUP. Bottom: Light microscope images of fresh (unfixed) cells in valve (left)
and girdle (right) view.