All those white things zooming around in the water column whilst the baby bloody mary cherry shrimp hangs out on one of the roots of the Java fern (Microsorum pteropus ‘Windelov’ ) are copepods!
Unintentional yet still welcome residents of the Shrimphaus, copepods are a form of zooplankton. Like their much, much larger relatives the shrimp, copepods are also crustaceans, and also have ten (?) legs, an exoskeleton, the whole works. Copepods tend to be sub-millimetre in length, whitish looking, and capable of very rapid jerky movement covering several centimetres at a time, making them the fastest animals on the planet (in terms of body lengths travelled per second). Happily, copepods eat algae from the water column so can be considered members of an aquarium clean-up crew. They are a highly nutritious food source for fish, but I don’t think the shrimp eat them.
In the pictures above, both copepods are photographed at 10x optical zoom. Both are “heading” to the upper right. The female has two egg sacs to both the right and left of the bottom bit. The male? copepod doesn’t have these, but that might simply be a female that doesn’t have eggs. These two were resting on the surface of the glass; the ones swimming around in the water column don’t photograph very well…
Copepods are abundant in the Shrimphaus but I haven’t ever noticed them in the Fireplace Aquarium, either because they were never introduced in the first place, or because the fish do a super-efficient job of keeping the population down. I might try a water transplant from the Shrimphaus to the Fireplace Aquarium at some point to cross-introduce these little guys.