Red goo of doom

If you've seen and/or read H.G.Wells' War of the Worlds, you'll know about the alien red substance that creeps and raminates... if not, I recommend a library near you. In any case, when I saw a fairly uniform red growth in water on a polythene cover in our garden, (a) my sci-fi nerdery kicked in, and (b) I had to see what it really was.

Mystery red goo in a thin layer of rainwater.

 I did wonder if it was bacteria, and took a sample for a look under the microscope.

At x40, small round red structures are seen.

At x100, these show some faint internal structure.

Using the camera to zoom to about x250, this creature was seen, alive but contracted.

At this point, I knew that is wasn't bacteria (well, I'm sure there is some too) but a rotifer, probably Rotaria sp. These can be found in mud, detritus, among moss and in free-standing water as here. If their thin layer of water dries out they can form resistant cysts and re-emergence when wetted by rain - it is possible the red structures are cysts as rotifers can be very numerous. Rotifers as a whole are small (almost all smaller than 1mm, and some a tenth of this) and found in almost any wet or damp habitat. Some genera are benthic/littoral, some are planktonic, many include both benthic and planktonic species. Most rotifers seen are female and reproduce parthenogenetically (i.e. without needing to mate), while males occur sporadically and often seasonally, and being smaller are less often found. However, males are not known for the bdelloid group in which Rotaria is placed. So, presumably the photos here are all of females!


There isn't space for a detailed look at rotifers here, but if you want to be able to identify British freshwater planktonic species (e.g. those found in ponds), then Pontin (1978) is a good starting point.

While some move with cilia, others, as here have a 'foot' like a mollusc and move using this, being able to contract and expand their body.

Rotaria extended and curled. Various structures are visible - the head is blurred bottom-right - moving left, the paired jaws can be seen.

Rotaria extended, head towards the bottom.

Next post - back to the macroscopic world!

Reference

Pontin, R.M. (1978). A Key to the Freshwater Planktonic and Semi-planktonic Rotifera of the British Isles. FBA, Ambleside.