I've long been fascinated by heliozoans aka 'sun animacules' and have posted on them before, but thought I would again because I've captured some pictures of one without squashing it under a coverslip - and also photographed it digesting its last meal. Briefly, heliozoans are single-celled amoebae which, instead of flowing around and engulfing their food with cytoplasmic arms called pseudopodia, radiate spines of cytoplasm supported by an internal scaffold of microtubules. They roll through the water like a one-tenth-of-a-millimetre-in-diameter sea mine, bringing dead to anything small that contacts those spines. This is a through-focus sequence of this microscopic protist menace, so in the image above we are looking down on the upper surface, onto what looks like a sphere of cytoplasm radiating needles in every dimension...
.... and here the focus has moved down a bit, onto the surface of that cytoplasm, which is broadly divided up into a pattern of hexagonal blisters....
.... and now we are looking at the contents of its central food vacuole - and this heliozoan has somehow managed to ingest a testate rhizopod - a form of amoeba that lives in a shell shaped like a hot air balloon. Incidentally, all the pictures on this post will be clearer if you double-click on them to enlarge them in a separate window. Below is the same sequence, but this time at x400 magnification instead of x100......
..... so here are the surface hexagons, with the base of those lethal radiating spines....
..... and here is the blistered pattern - which looks like cells but this is a single-celled protist - so they must be formed with the aid of microtubules, I guess ......
.... and here's its food vacuole, with ingested testate rhizopod. It will digest the cytoplasm of its prey and spit out the empty shell.
It's easy to loose a sense of scale when peering down the microscope at small organisms - a sense of their place in the universe. So the picture above shows the place where this 100 micron predator came from - from the moss around the edge of this small pool on bleak moorland in Weardale, County Durham . The pool is about a metre long, so if you lined up 10,000 heliozoans spine-tip-to-spine-tip they'd stretch from one end to the other ....
..... and that tiny pool is somewhere in the middle distance in this landscape ......... and beyond that the solar system and beyond that the universe, home to an exquisite tiny life form that has been rolling through our planet's water, ingesting whatever it touches, for well over a billion years. Time travel is possible if you have a microscope....
