Sunday, May 22, 2011

Life in a few Drops of Water: Desmids

This is the second in the series of images of some of the organisms found in just a few drops of water collected from a pond in a disused quarry on the edge of the moors in Weardale.
This is  a desmid - probably a species of Cosmarium. Desmids are typically constricted in the centre of the cell to form two mirror-image halves.

These are single-celled, photosynthetic algae that often have a patterned cell wall that's ...

.... most clearly visible after the cell has died and lost its chlorophyll.

This appears to be one half of a desmid that has broken at the bridge joining the two halves (known as the isthmus), revealing the fractured hole.

Coming next: Dinoflagellates

Tuesday, May 10, 2011

Life in a Few Drops of Water: Diatoms

A few days ago, when we were out walking in Weardale, I collected a small sample of water from a pond in a disused quarry on the edge of the moors, then spent several hours that same evening exploring just a few drops of the pond water - maybe ten in total - under the microscope. The organisms pictures in this post are all diatoms - minute photosynthetic organisms encased in a shell of pure silica that often bears the most intricate pattern on its surface. This one, caught in the act of dividing, is Pinnularia.


Some are long and thin (this is Nitzchia sigmoidea), while.....

....others are joined together in chains.

Navicula? When diatoms die their silica shell remains, almost indestructible, and in that transparent state, with no contents, the full beauty of the sculpturing on their shells can be appreciated.

The pattern of fine ridges on Cymbella tests the ability of microscope lenses to resolve such fine detail.

Diatoms generally move in a gliding motion through the water but sometimes they can be attached to a substrate via mucilaginous stalks.....

... seen here at higher magnification.

Most of these organisms are less than one twentieth of a millimetre long.

Coming next: Desmids....mirror-images in miniature