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.

Anticlockwise tubeworms

The calcareous spiral tubes of tubeworms, attached to wracks and kelps that are washed up on the strandline, are a common sight on the seashore. There are several different species and the first step to identification is to see whether the tube coils clockwise or anticlockwise. If it's clockwise, then it'll be a species of Spirorbis but if it's anticlockwise, like these, and the tube has three distinct ridges, then it's a worm called Janua pagenstecheri. The coiled tube is about 2mm. in diameter.

If you watch the live worm under the microscope it soon everts its crown of transparent feeding tentacles. If you look just to the right of the tentacles you can see a brown, translucent flap. This has a dual function, closing off the tube when the worm withdraws its tentacles and acting as a brood chamber for the worm's embryos. The pink encrustation in front of the worm is a alga, not part of the animal.

Another Living Jewel

My last post showed a jewel-like case made by a single-celled amoeba. This one shows the remarkable case made by a marine worm.  We found this little tapered tube, about 5 cm. long, on the sandy beach at Warkworth in Northumberland this afternoon. It was made by a worm called Pectinaria koreni and when the animal inside is alive only the last few millimetres of the narrow end of the tube protrudes above the sand. The worm lives head-down in the sand, drawing in a current of water through the narrow end of the tube.

You can see the dark zone at the narrow end here - that's the bit that normally protrudes above the sand. The tube is made up of hundreds of sand grains and minute shell fragments, selected for smoothness inside and outside the tube and ....

.... neatly fitted together with a degree of precision that a stonemason would envy....

 

.... and although the tube is only one sand grain thick it's remarkably strong. That's because....

... the worm secretes a form of cement that glues the grains together, like mortar in a wall ......

.... as you can see here at higher magnification.

A pair would make rather fine ear-rings, provided the wearer didn't have any qualms about wearing jewellery made by a worm rather than by a jeweller.

You can see a picture of the worm here.