âI think weâve read every single book they have.â Mark chuckled. He still wasnât ready to put the children downâWill was hanging off of one hip, his hand on Markâs shoulder as he stoically looked down at Bridget, and Mabel had nuzzled into the crook of Markâs neck with a contented sigh.
Diatoms are producers within the food chain. A unique feature of diatom cells is that they are enclosed within a cell wall made of silica (hydrated silicon dioxide) called a frustule. These frustules show a wide diversity in form, but are usually almost bilaterally symmetrical, hence the group name.
Diatoms range considerably in size, the largest species being about 2-mm and the smallest being only a few micrometers long. The âpennateâ diatom shown below is a little over 200-micrometers long. Such long, skinny pennate Diatoms are the most common form. Equally common is the gold or yellow color. This is because they have a large amount of yellow carrotenoid pigment and xanthophyll pigment that masks the green color of their Chlorophyll. Many Diatoms are motile, moving slowly, but steadily. Motion can be useful, if you live at the bottom of a pond and need to get from a dark areas to the sunlight. Diatoms are very difficult for us ordinary mortals to identify, since their body plan is basically quite simple and they are, pretty much, all the same color. The two tests fit together like the two parts of a Petri Plate, and the assembly is called a âvalveâ. Essentially, Diatoms are either pennate or âcentricâ.