Favoritos de peptolab

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.

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!

Aspidiophorus paradoxus is the largest Aspidiophorus species with about 300µm length.

Fig. 1: Dorsal scales.

The entire animal is covered with relatively large rhombic peduncle scales.

Fig. 2: Cross section

In cross-section, the structure of the peduncle scales can be clearly seen: the scales sit with a small basal plate on the cuticle of the animal, from which a thin, hollow peduncle rises. At the end of the peduncle sits a rhombic terminal plate, with a central keel. At the posterior end of the animal, the terminal plates of the last row of scales are enlarged.

The pharynx of the animal is terminally swollen, and the head is weakly five-lobed with two separate pairs of palpal tufts.

Fig. 3: Ventral view.

Ventrally, the strong hypostomion behind the mouth opening is striking. The two ciliated bands split at the head, but the inner branches do not unite in the population I examined. The base of the toes does not bear scales, the adhesive tubes
measure about 50% to 70% of the toe length and taper to a point.

Let's take a closer look at the scales:

Fig. 4: Back scales

In the scales on the back, the rhombic shape of the end plates can be seen most clearly. Less conspicuous - but typical for the species - is the middle keel of the scales.

Fig. 5: Cross section of scales

In cross section the complex geometry of the peduncle scales becomes clear - base plate, peduncle and end plate form a very flexible and stable carapace. The additional cavity under the outer scales acts like a "crumple zone" and further increases the protective effect.

Fig. 6: Cross-section of scale stems.

The stems of the scales consist of hollow tubes that ensure maximum stability with minimum material input - a fascinating example of evolutionary optimization.

The abdomen of the animals is not completely covered with petiolar scales. Rather, they end in the anal region and are joined by simple small, rounded keel scales that are not an obstruction to feces.

Fig. 7: Scaling of the abdomen.

At the furca base some (according to literature 4) spines protrude into the toe cutout.

The head is almost completely covered with slightly smaller peduncle scales:

Fig. 8: Head scales

Cephalion and pleurae are quite small and inconspicuous.

According to literature A. paradoxus has three teeth in the pharynx:

Fig. 9: Mouth armament.

In the animals I examined, only a curved stylet brace was found, the tip of which protrudes into the lumen of the pharynx and probably serves to open algal cells that are conveyed past it. It is possible that the literature reference to "three teeth" is merely based on a microscopic artifact, as the entire clasp may not be in the focal plane as a whole.

Mag. 400x
For reference images see http://www.digicodes.info/Micrasterias_muricata.html. This taxon has been observed in 2 nearby waterbodies: https://www.inaturalist.org/observations/132612551 and https://www.inaturalist.org/observations/105465282.

• A water sample was taken on 5/8/2023, from the shore of Lantern Hill Pond, using a 10µ dip net to enrich for microbes. Air temp. 73°F.

Mag. 400
The interesting thing here is that this rotund ciliate has swallowed Peridinium-like, freshwater dinoflagellate; this is the large brownish mass... in the 2nd image, the girdle of dinoflagellate is readily visible.

• A water sample was taken on 1/24/2023, from the shore of Rosemond Lake , using a 10µ dip net to enrich for microbes. Air temp. 42°F.