Middle-earth came to Regular Earth this spring when not one but TWO species sporting Gandalf’s wizard hat made the rounds.

One was a sea cucumber who only coincidentally appeared to be sporting the iconic headwear. But the other is a microbe whose shell really does bear an uncanny resemblance to the weather-beaten wizard topper. It is Arcella gandalfi, a new South American shelled amoeba.

Shells built by six different individuals of A. gandalfi. Scale bar 20 micrometers. Credit: Féres et al. 2017
Scanning electron micrographs of A. gandalfi showing the hole where the amoeba protrudes from its shell. Lower image shows the individual hexagonal panels of organic material that build the shell and how they are elongated near the crown of the "hat". Scale bar 20 micrometers. Credit: Féres et al. 2017

A close relative, Arcella brasiliensis, was already known, but has more of a brimmed beanie thing going on.

Arcella brasiliensis. Image at left shows "hat brim" and central hole. Scale bar 20 micrometers. Credit: Féres et al. 2017

Inside these crazy shells live amoebas. They are just like the amoebas you may recall from school, with the blobby lobes and the food engulfment meal plan. Have a look at the logo of this blog to refresh your memory.

However, unlike the garden variety amoeba, these amoebas live inside shells, just like the animals inside sea shells (scientists call amoeba shells tests, and the group organisms “testate amoebae”; I wrote a short piece a few years ago about their use in dating corpses for Scientific American magazine). Presumably, amoeba shells serve the same function as seashells: mobile home/security system.

We can infer a close relationship between A. gandalfi and A. brasiliensis not just due to their hat-like appearances, but also because the shells share similar “brims”, which the scientists called marginal rings. Of all the known testate amoebas, only these two species have them.

Marginal ring (hat brim) of A. gandalfi. Aperture (harder to discern) at center. Scale bar 20 micrometers. Credit: Féres et al. 2017

The two species share more in common than just a brim, of course. All of the more than 130 species in the genus Arcella live in still and running freshwater and around mosses, plant roots, and plankton. They are all roughly hemispheric in side view and circular when viewed from below, and they are built of hexagonal organic panels secreted by the cell.

In this image of the top of the wizard hat of A. gandalfi, you can see those panels clearly.

Top view of shell of A. gandalfi. Scale bar 20 micrometers. Credit: Féres et al. 2017

But like most testate amoebae, species of Arcella are hard to tell apart. They are poorly studied, which makes differentiating them a challenge, but their shells also tend to vary within a given species, probably due to the different environmental conditions in which amoebas manufacture them.

For the species A. gandalfi, this is not a problem. Its unmistakable profile make its members highly recognizable. The fact these shells are also large (for an amoeba, that is -- 70 x 80 micrometers or so) and seem to be found only in South America (actually, only in five states in Brazil so far, since they were the only places sampled for this study) could make A. gandalfi a good “flagship species”, the describers argue.

The question of whether some microbes are actually limited to certain geographic regions, and not present everywhere on Earth and just selected by the right environmental conditions, is one that has dogged microbiology. For most simply-shaped microbes, this is fiendishly difficult to discern.  

Since the odds seem high that someone would by now have recognized a wizard-hat shaped microbe shell in the Northern Hemisphere and described it, the thinking goes, such “flagship” species could be proof that a microbe is actually geographically limited -- in this case, to South America, or perhaps even just Brazil. On the other hand, other microbe species have been nominated for this role before, only to be discovered upon closer inspection back in good ol’ “over-studied” Europe or North America after all.

Assuming A. gandalfi is actually unique to South America, it could one day help bolster claims that that at least some microbes are like platypuses, corpse flowers, and craft beers: distinctive and available only in limited release in a restricted area.


FÉRES, Jordana C., Alfredo L. PORFÍRIO-SOUSA, Giulia M. RIBEIRO, Gustavo M. ROCHA, José Mauro STERZA, Maria Beatriz G. SOUZA, Carlos Eduardo A. SOARES, and J. G. Daniel. "Morphological and Morphometric Description of a Novel Shelled Amoeba Arcella gandalfi sp. nov.(Amoebozoa: Arcellinida) from Brazilian Continental Waters." Acta Protozoologica 2016, no. 4 (2016): 221-229.