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I used a 1967 edition of the Observers Book of Pond Life to identify this species so nomenclature may have changed since then. (still the best freshwater ID guide around though!)
Dear Bob, The guide worked for this species! I'm absolutely certain that that's the correct species now.
This is policelis nigra. The other common, small, black flatworm is P. felinis. However, P. felinis has 'ears', short tenticles either side of the the anterior end of the animal. These look vaigely like cat's ears, hence the scientific name, felinis.
I catch lots of both when pond dipping with kids and adults. They are often mistaken for leaches but have a very different way of moving. Leaches contract and stretch like some caterpillars and the inch worm of the wonderful 1952 Danny Kaye musical, Hans Christian Anderson. Some leaches also swim freely in the water, especially horse and medicinal leaches. Flatworms, on the otherhand glide over the bottom of the pond hardly ever swimming free in the water.
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Dear Graham, thank you for the correct scientific name.At first when I saw it I thought it was a leech![I only found out it was a flatworm when we looked it up on the web.]
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