Spying on an underground community

So, I've been trying to take photos in the dark. Not dark dark, midnight dark, but in shadow, illuminated only by a weak, yellowish overhead light, and dimmed even more when I used an auxiliary lens. And I couldn't use flash*.

See, the floor of the aquarium is covered with 2 inches of sand (more or less, as the crabs dig out valleys and hills). I brought the sand from their home territory, in the upper intertidal zone of Boundary Bay, draining off the fine sediment and muck before I used it. It was "live" sand; I reserved a half-cupful and left it overnight in a white bowl. In the morning, tiny, pinpoint snails were climbing the walls, and a few worms had re-established their tubes. Their tentacles, fishing for food, were only visible with my hand microscope.

All to the good; worms in the sand clean up tiny bits of food that the hermits and crabs scatter. (Messy eaters, the lot of them!) Along with the mud snails and Nassas that plow through the sand looking for food, they help to keep the sand oxygenated, so that it doesn't develop those stinky, black dead zones that we find on the beach where the sand is too compacted.

Within days, the sand in the aquarium was riddled with hair-thin worm burrows. Some are right up against the glass wall, and I have been watching them.

The problem is, they don't like light. Very emphatically, they do not like it. Move the lamp so that light falls on the glass, and they're gone, retracted back into the dark sand. They're fast. All I usually see is a hint of moving colour at the bottom of the burrow, then nothing.

The camera is better than my eyes, even here. I set the camera down an inch from the glass, focused, held the focus so that the worms that fled the red focusing light could return, then pressed the shutter. Click ... ... ... ... click. I didn't release the shutter until the second click, to avoid shaking the camera while it worked on the scene. (The little pocket Sony was better at this than the bigger Nikon.)

Here are the results.

What the camera saw in the dark. Burrows and red worms. Some light percolates down through the top half inch of the glass wall.

I get the camera ready, finger on the shutter button, and turn on the light. This is what I see:

Empty burrows. A hint of red at the bottom of the long burrow on the right; a slowpoke worm.

Clean, nicely rounded tunnels. The worm wobbles its body back and forth to shape the sides. 

The tunnels are now about as wide as a line written by a fine lead pencil. The worms are obviously eating well and growing fast. The longest burrows are about three inches long, taking their meandering into account. They each open at the top onto the surface of the sand, and I have seen a couple at the opening, fishing.

I cropped the clearest photos, lightened them 'way up, and saturated the colour in the worms to compensate. As far as I can tell, there are three species of worms.

A long, smooth, round worm, lightly marked on the red. Lugworm?

A couple more of the long ones, and a short, fat worm (or segment of worm), much redder. It has some projections at the sides, parapodia, probably. Another polychaete?

Another of the long, smooth worms, head and tail both in the sand.

In the top right corner of the first photo above, there is a stripy worm. Here it is, magnified.

There were also a few translucent, unmarked, very smooth-skinned worms, just slightly pinkish. The cameras absolutely refused to take notice of them. At this size, I can't identify any of them.

And no wonder I can't find any on the beach; they are too fast for human hands, mostly too small for human eyes even when I do dig them up.

* The flash would have bounced off the glass, and made everything inside invisible.