Bring 'em Back Alive - Uhlig Extraction

Created by Lorraine Olendzenski, St Lawrence University

The spaces between sand grains and other sediments can harbor abundant protists and bacteria. Protists, especially ciliates, can be extracted from their interstitial environment for observation by the following technique. This modified and simplified "Uhlig ciliate sandy sediment separator" is primarily for the extraction of ciliates from marine and estuarine fine grain wet sandy sediments.

Materials Needed

  • Two plastic cups that can be cut with scissors or a razor blade
  • Nytex nylon mesh or other loosely woven fabric or mesh
  • Small petri plate in which bottom of cup can fit
  • Standard size petri plate


  1. Take two plastic cups of the same size and remove the bottom with scissors or a razor blade. In one cup, cut two small (approx. 5 mm size) triangle-shaped notches into the bottom edge, directly opposite each other.
  2. Place a square of Nytex nylon mesh, or other loosely woven fabric or mesh, tightly over the bottom edge, directly over the bottom opening of the unnotched cup. Place this cup and the mesh into the other plastic cup.
  3. Place a moist sand sample within the inner cup. Place the whole plastic cup assembly into the bottom of a small petri plate. Add water from the sample site into the bottom of the petri dish so that the water is in complete contact with the bottom of the nylon. Add more of the same water to the upper surface of the sand sample until the inner cup is full. If using this method, an overflow of water will be needed. Place a large (standard) size petri plate under the smaller petri plate. The other half of the standard size petri dish can be used to cover the inner cup so as to prevent dehydration.
  4. Extraction sampling is accomplished by carefully removing the small petri dish and observing under a dissecting microscope. Individual ciliates can be removed with a micropipette and placed on a microscope slide with coverslip for high-powered observation (this requires some patience and skill). Another petri dish can be placed under the device and more water poured through the sediment (or the overflow water can be poured through the sample again).

Helpful Tips

  • Sand samples from various depths can be sampled by slicing cored samples and placing each into its own Uhlig extractor.
  • Ciliates are generally positively geotropic and will migrate out of the sand at different rates of speed and at different times. Therefore it is best to sample the separator at time intervals (e.g. 6, 12, 24, and 36 hours). The method works well for freshwater, brackish, and marine silicate and carbonate sandy sediments.
  • Ciliates will also move in reaction to salinity and temperature gradients. Another method of extracting organisms is to place frozen sea water ice cubes onto the surface of the sediment. As they melt, the ciliates will move out of the sediment and into the water below.


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