Face to Face: Bdelloidea (Rotifera)

Bdelloidea

Somewhere in this grainy horrible picture there's a rotifer. Well, at least you can distinguish the foot, the trunk with the stomach full of unicellular algae and the head with the corona of cilia.

If you think the photo above is the most heinous example of bad microphotography on the web, you’re probably pretty close to the truth; don’t be too harsh, though: it’s pretty good, considering the circumstances. First, it was basically my first try at photographing something through the microscope; second, the microscope itself is a pretty old and not too great, and the camera was a normal, cheap digital camera; third (and most important), at the time I hadn’t any microscope slides, so I used some pieces of old transparent plastic I cut from who knows where. So, considering all of this, it’s not too bad, right?

I was tempted to take this photo even in those unfavorable conditions because the animal itself was pretty spectacular, and that was the first (and for now the only) time I had seen a living specimen of this kind of organisms – although they certainly aren’t hard to find at all: it was sufficient to leave a glass full of water and a handful of potting soil out of the window for a few days, and I created a perfect microhabitat for these creatures, along with various protozoa and algae.

It is a bdelloid rotifer (class Bdelloidea, phylum Rotifera): this particular class is completely parthenogenetic (they’re all females that give birth to other females without the need of males), and thus they’re studied by evolutionary biologists interested in the role of sexual reproduction in evolution. Rotifers (which are pseudocelomate and have a cuticle, just like nematodes) have a muscular foot with which they can attach to the substrate or “walk” on it, a usually roughly cilindrical body and two other features that sadly (they were the coolest to watch in action) aren’t visible in this blurry photo: a calcified masticatory organ called mastax, which I could see through the transparent pharynx of the animal, endlessly chewing the single-celled algae it was eating, and the corona, a ciliated structure on the head: the cilia are constantly moving to bring food particles to the mouth or to allow the animal to move through water, and they give the impression that the roughly round-shaped head of the rotifer is a constantly rotating wheel (the name “rotifer” basically means “thing that has a wheel”). Rotifers are an important piece of freshwater ecosystems all around the world, regulating the composition of phytoplankton and contributing to nutrient recycling – their proliferation, along with the proliferation of certain bacteria and protozoa, is even stimulated to purify wastewaters during the process of activated sludge.

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One comment on “Face to Face: Bdelloidea (Rotifera)

  1. […] Or when I shamelessly analyzed the biology in Avatar. And what about my clumsy attempts at microphotography? Not to mention the most awesome environmentalist ad ever made, and my encounters with rare animals […]

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