Observações de bdstaylor

A testate amoeba from a forest fen in Wakefield, Quebec. The specimen was air-dried and imaged in a scanning electron microscope at the Canadian Museum of Nature.

The image shows two features that differentiate Galeripora from its cousin Arcella: 1) an organic coating on the outer ventral surface of the shell, obscuring the hexagonal units out of which it is composed; and 2) small pores encircling the aperture.

The shell of a testate amoeba from the Mer Bleue conservation area. Specimens of Netzelia corona often form agglutinated shells, incorporating found particles. However, they can also form lumpy "tuberculate" shells composed of secreted organic material (similar to Netzelia tuberculata, which is also very common in Mer Bleue samples). This one incorporates a few large grains of sand around the aperture, but is mostly tuberculate.

Samples were air-dried and imaged in a scanning electron microscope at the Canadian Museum of Nature.

The shell of a large testate amoeba (~360 µm) from surface water in a cattail marsh in the Mer Bleue Bog conservation area. The shell was air-dried, then imaged in a scanning electron microscope at the Canadian Museum of Nature.

A few more specimens of Ileonema dispar, the type species of the genus, which, as far as I know, has not been recorded since it was discovered by Stokes in 1884. It is differentiated from I. simplex by its flagellar process, which, in the species Stokes describes, is in two distinct parts, thick at the base and finely filamentous at the distal end (Stokes, 1884; Penard, 1922; Kahl, 1930). This is reflected in the name of the species, "dispar" (=unequal). Stokes also describes the species as having two contractile vacuoles in the posterior, an arrangement that would be extremely odd for a trachelophyllid ciliate. In several specimens, I observed some compartmentalization in the posterior vesicle, which could easily be read as two separate vacuoles adjacent to the "anal pore." See image #4.

The flagellar process is retractable, and its appearance is quite variable. The division of this organelle into two distinct parts--which I did not see in every specimen--strikes me as a weak character. As I noted in my previous observation, I think there is some reason to think that I. simplex should be considered a junior synonym of I. dispar (or possibly a variant, or sub-species).

I caught one in fission, and have included two images of the dividers.

I also watched an individual eating a huge clump of debris containing living and dead algae. This observation, and the contents of the cytoplasm in other individuals, lead me to think the critter lives by consuming small round green algae.

A ciliate with a curious flagellum-like process at its anterior. This structure is not a true flagellum. It does not move independently, but simply dangles from the ciliate's mouth as it swims around. Its purpose is not known. In other respects, Ileonema closely resembles Trachelophyllum. Like members of that genus it is enveloped by a coat of ornate epicortical scales, visible only in the scanning electron microscope. (See Foissner's monograph on Terrestrial and Semiterrestrial Ciliates from Venezuela and Galápagos, pp. 50ff)

Ileonema dispar is the type species of the genus, which was erected in 1884 by Alfred C. Stokes. In 1922, Penard described a similar species under the name I. simplex. I think there reason to believe that I. dispar and I. simplex are the same species, viewed in different conditions. Penard observed only one specimen, although he was able to watch it for a couple of hours. Stokes found I. dispar "in abundance", and describes it as having a variable shape: "Its changes of form are...quite constant as it rests among the algal threads and lengthens the entire body into a club-shaped creature searching for food, or contracts into an egg-shape with a short, narrow neck." However, he only illustrates one specimen (a rather pudgy one!), and it is this illustration that was reproduced in Kahl, with a short description (Kahl does not seem to have found the organism himself). Stokes also observed that his Ileonema is nearly identical in overall appearance to Trachelophyllum apiculatum: a telling comment, since the latter is usually quite slender, like Penard's simplex.

Stokes describes the "flagellum" as follows: "entire flagellum one-half the length of the body, the basal half thick, obliquely grooved and presenting a twisted or cord-like appearance, slightly tapering yet suddenly constricted at the beginning of the finely filamentous distal one-half."

The "flagella" of my critters are generally shaped much as Stokes describes: quite thick at the proximal end, finely filamentous at the distal. Seeing them at low magnification, it's easy to see how he might have misinterpreted the flagellum as being twisted, or ropelike. In my observations, the flagella of some individuals, at certain levels of illumination, appear to be quite uniform from base to tip.

The Ileonema in my population are also extremely contractile, ranging in shape from plumply ovoid to gracefully attenuated and vermiform. After they've eaten, they become almost unrecognizable!