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