The mysterious

'carpenter's rule' diatom
Bacillaria paradoxa (now known as Bacillaria paxillifer)

by Wim van Egmond



 

a colony of Bacillaria almost at rest, photographed with phasecontrast, 40x objective

For people who are used to firm-rooted trees and shrubs, looking through a microscope can cause a bit of a surprise. Microscopic plants are not that immobile. Many kinds of algae do move and some of them in an extraordinary fashion.
Watching the movement of Bacillaria paradoxa is one of the most intriguing sightings you can experience when looking through the microscope. It is a small colony of pennate diatoms that moves like it is one of the latest technological inventions. The individual diatoms slide back and forth over one another so the shape of the colony can change from a square to an elongated pen.


       


Two colonies entangled, photographed in black and white, made duotone with Photoshop

Many algae are mobile. The most obvious are the flagellates propelling themselves with a whip-like organ. But also desmids, diatoms and bluegreen algae have a mechanism for movement. How diatoms move is not completely understood. Only the pennate ones can. It seems that through the groove running in the length of the cell wall, called the raphe, tiny fibrils protrude that vibrate in one direction. The diatom can move slowly into two directions over a substrate.

In Bacillaria paradoxa the individuals move from one another (so the normal speed of locomotion is multiplied) and therefore can reach turbospeed compared to normal 'solo' diatoms. I found Bacillaria in marine water using a plankton-net. They can also be found in brackish almost fresh water. They have the ability to stick to the substrate so it is sometimes rather difficult to catch them with a pipette. When you finally think you've got it it sticks inside the pipette.

The name Bacillaria paradoxa is not correct anymore. It should now be called Bacillaria paxillifer. Could this have something to do that scientists don't like paradoxes? Why discard a name that covers the content so well.

Diatoms are wonderful objects under the microscope. More about them can be found in the following articles articles:
Marine Diatoms, Those who live in glass houses and Art Deco Diatoms


 


Coscinodiscus, a centric diatom, showing both the inner structures (chloroplasts) as the cell wall

Many amateur microscopists tend to clean their specimens with chemicals before observing them. This seems an odd thing when you realise that you miss half of the organism and see only it's coat. The shells of diatoms are indeed beautifully ornamented. But this can also been seen when the living tissue is still in it. The way the chloroplasts lie inside the shell is in fact very beautiful too. And watching Bacillaria and its relatives move is a fantastic sight. Forget the chemicals for a few hours and watch these marvels alive!

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