Fascicle

Series, or bundle, of rows of areolae oriented radially in some centric diatoms.

Ill2011 41  Steph Niagarae6
Image Credit: Sarah Spaulding
Stephanodiscus niagarae is characterized by fasicles of 2-3 rows of areolae.
Costae
Image Credit: Sarah Spaulding
Detail of S. niagarae, with the costae, or interfascicles, marked in red. The costae separate the fascicles of areolae.