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Diatom on a stalk, in slime

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Here’s a diatom (alga in a glass case), probably Cymbella sp. (apparently also called “rock snot”…),  sitting atop a stalk of mucilage. These diatoms can sometimes be seen on rocks in creeks and streams as fuzzy brown stuff growing, comprised of large colonies. In masses, they are also extremely slimy — perhaps you have unknowingly received damage from these critters making you slip and fall. The brown stuff is the plastid itself, taking up much of the cell — you can almost make out the thylakoid stacks as fine striations on the top part, where the plastid curls towards you, providing us with a handy cross-section. Energy is stored in the fat globules seen in the middle of the cell. The very centre contains the nucleus, which is not visible in this section. Diatoms are much thicker than we like to imagine them, sometimes thicker than they are wide. Surrounding the frustule (glass case) is more mucilage, seen as that faint outer contour. This probably is what makes their masses exceptionally slimy — you’re stepping on layers and layers of glass cases embedded in balls of mucus. In other words, avoid stones covered in brown fuzz when crossing rivers — to prevent crushing innocent colonies, of course, rather than anything to do with self-preservation.

Psi Wavefunction About the Author: Psi Wavefunction is a graduate of the University of British Columbia working as a protist researcher (soon to be graduate student) at Dalhousie University in Halifax, Nova Scotia, and blogs about protists and evolution at The Ocelloid as well as at Skeptic Wonder. Follow on Twitter @Ocelloid.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. Planapo 4:23 pm 02/17/2013

    Greetings,Psi. Agree that your stalked diatom is Genus Cymbella, but this is not “Rock snot,” or Didymosphenia geminata. Didymosphenia is another stalked diatom, which forms a colony that looks like a wet sheep’s fleece, not a property of any Cymbella that I know of. Image FYI is here: http://www.olympusbioscapes.com/gallery/2010/hm36.html

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  2. 2. Psi Wavefunction in reply to Psi Wavefunction 7:16 pm 02/17/2013

    Thanks, good point — and that’s a pretty picture you linked! I have seen similar Cymbella-like diatoms in samples extracted from very slippery rocks, growing in patches of fuzzy brown stuff (could be mixing things up though, am bad at diatom ID), but upon googling Didymosphenia — wow, that stuff is impressively snot-like! (example) The mucus-y aspect still applies from the stalks though, I’d imagine, just no mucus around the individual frustules. Apparently quite a pest in some areas — which makes sense, given how weedy diatoms can get when you’re trying to culture other things

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