Re: How large can amebas get?

There are many kinds of amoebas (I don't know why the 'o' got into this 
word) but I divide them between naked and shelled types.  Most naked types 
are small to medium sized (10-40 micrometers) but one big species often used 
in biology labs is almost 1000 micrometers (1 millimeter) in size.  Then 
there is Pelomyxa, an unusual amoeba that is killed by oxygen, forcing it to 
live in  mud on the bottom of ponds.  It can be from 1-2 mm, and totally 
lacks any mitochondria but has many many nuclei, each surrounded by 
bacteria.  

The biggest amoebas of all are shelled types called foraminifera (or 
"forams") that made calcium carbonate shells.  While some forams float in 
the ocean, giant species live on the bottom of shallow ocean water, where 
they are larger than 2 mm.  A giant extinct species once grew to 10 cm in 
width!  The reason it could grow so large is evidently the help it received 
from countless tiny diatoms (photosynthetic algae) that lived within the 
foram, as is the case with smaller (but still very large) surviving forams.  
Since the giant foram was shaped like a coin, round and flat, they are 
called Nummmulites (coin collectors are called numismatists).  These forams 
lived in such vast numbers that their dead shells accumulated into thick 
layers that later turned to limestone; the pyramids of Egypt were 
constructed with such "amoebic" limestone.