Sunday, October 6, 2013

A tiny aquatic worm that clones itself

All summer, small containers of various kinds in our garden have collected rainwater and detritus - and each of these microcosms has developed a fauna of its own. This is a little oligochaete worm called Aeolosoma that I found in the layer of mouldering leaves at the bottom of one of these little pools.

Oligochaetes are annelids (segmented worms) whose bodies have only a few bristles on each segment. This species, less than two millimetres long, is almost completely transparent and has distinctive little orange spots just under the body surface. If you look closely you can also just make out the fine bristles at the junctions of the body segments. It whisks food into its mouth, which is under and towards the back of that spade-like structure called the prostomium, with fine cilia that beat and generate a water current. It's thought that that spade-like prostomium can attach like a sucker to a substrate so that the beating cilia generate suction, aiding feeding.

Aeolosoma divides asexually, budding off new individuals from the tail end, so it's quite possible that the thriving colony (I found six in a single drop of water so there must be thousands in the container) are all descended from a single original colonist.

In the image above you can see the prostomium being used rather like a vacuum cleaner nozzle.

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