Friday, 25 November 2011

Freshwater Flatworms

 If you kneel down on the edge of a clear water pond and look towards the bottom, even at this time of year, you might be able to see some flattened elongated creatures slithering over the sediments, like they are levitating (above). They are planarians or flatworms. On closer inspection they have a quizzical look due to their simple eyespots or ocelli, which appear to be both looking inwards. They are relatively simple organisms, which move over a carpet of cilia and have simple guts, with a single opening, the mouth, which is sometimes placed in the middle of the body. I am trying to get some shots of water slaters and I have set up a little tank at home. Most of the time when I get some decaying leaves from my half barrel (=minipond) a few flatworms are accidentally transferred with them, and then I can take some photos of them while they climb on the walls. There appear to be several species, but yet have to find out some resources to tell them apart.
One of the most striking features of flatworms is their capacity for regeneration. If you cut them in half, each half grows the missing parts. Even a tiny part of a planarian can regenerate a complete individual.

2 comments:

Phil said...

Lovely picture showing the gut. There's a very useful book by Helen Mellanby, published in 1938 but running through 6 editions, the last in 1963, called Animal Life in Fresh Water, that describes eight species. Long out of print, but it sometimes turns up in second hand bookshops - although the names have probably all changed by now..

Blackbird said...

Thank you Phil, you are a star, that's so useful, I just ordered the last edition it by a fiver!