Protist Love 1--Difflugia!

This past week, I was checking one of my re-hydrated soil samples for the fungi my lab studies when I saw this organism. 

Difflugia sp. observed under brightfield from a re-hydrated soil sample. 400x

This is a testate amoeba. These amoeba build a home around themselves called a test. Tests are much like the shells of hermit crabs. This particular testate amoeba has built its shell out of quartz crystals, also known as sand. The materials and the shape of the test suggest this testate amoeba is a member of the genus Difflugia. 

Difflugia sp. observed with phase contrast. Note the pseudopodia (short, clear tube) beginning to emerge from the opening. 400x

In this photograph, you can see the opening in the test. The amoeba is just barely poking out--a bit camera shy. On a side note, the first image was taken using the brightfield of the microscope. This image, and the ones that follow, are taken with phase contrast, which changes the way the light passes through the specimen. The details are complicated (hard for me the understand), but the end result is that it is easier to see some things.

Difflugia sp. observed with phase contrast. Lots of  pseudopodia now ! 400x

As I watched, the critter, possibly aggravated by the light, began to come out of the test.

Difflugia sp. observed with phase contrast. Wondering where it's going.... 400x

Difflugia sp. observed with phase contrast. Those pseudopodia are long! 400x

Soon, it was crawling around, exploring the new environment of the microscope slide.

Intrigued, I looked up a bit of information on Difflugia. They are fascinating critters! Even though one might expect them to be heavy (their house is made out of sand), they are capable of floating. In fact, some species make a yearly trip to the water's surface in the spring to feed and then sink back down to the bottom in the fall. Gas or oil trapped in the test allows them to do this.

Difflugia migrate to the upper water layer (epilimnion) in the spring, following food. In the fall, it migrates back to the bottom (hypolimnion and sediments), also following food.

What really got me excited was their feeding behaviors. This genus regularly captures and eats rotifers and other eukaryotic microbes. The weird thing is that they eat them tail first. After coming in contact with the rotifer, the amoeba crawls to the back of it. If the rotifer is surrounded by a jelly tube, the amoeba rips open the tube. It grabs the rotifer by the tail and begins chowing down. Below is my cartoon version of what some recent authors (cited at the end) saw.

Difflugia sp. eating a rotifer, after Han et al. 2008 (cited below).

Apparently this has been known for a while as Penard (1902) illustrated a Difflugia sp. eating a rotifer. (If he didn't label it as such, I'd never have known.)

"Individu occupe a vider un petit Rotifere" (Individual occupied with eating a small rotifer) Penard 1902 pg. 216

Well, I didn't get to see that myself, but I did get to see something else pretty cool. I got to see the Difflugia launch itself from the substrate and attempt to float away.

Difflugia sp. observed with phase contrast. All systems check, it's time to go! 400x

Difflugia sp. observed with phase contrast. Gotta float! 400x

It couldn't float very well due to the coverslip, but it was cool nonetheless.


Further Reading

Penard ME. 1902. Rhizopodes D'eau Douce (or Faune Rhizopodiqu du Bassin de Leman).

Meisterfield, R. 1991. XII. Ecology of Aquatic Organisms. 3. Animals: Vertical distribution of Difflugia hydrostatica (Protozoa, Rhizopoda). Verh. Internat. Verein. Limnol. 24: 2726-2728.

Han B, Wang T, Lin Q, Dumont H. 2008. Carnivory and active hunting by the planktonic testate amoeba Diffulgia tuberspinifera. Hydrobiologia. 596: 197-201