Difflugia bacillifera Penard, 1890

Diagnosis: (From Penard,1890) Shell very elongated, pyriform, round in cross-section, formed by a very thin, hyaline chitinous membrane, entirely covered with diatom frustules, generally very large and arranged in a relative order along the shell, often mixed with very small round diatoms; occasionally, a few quartz fragments are also present. The aboral part is dome-shaped and adorned with smaller diatoms than those on the sides, while the anterior part is generally elongated into a narrow neck, truncated into a rounded terminal opening, which is almost always surrounded by a ring of very small round siliceous capsules (diatoms).

Dimensions: According to Penard (1890):  Shell length 150—170 µm; width 40—60 µm. Awerintzew: 150—190 µm. Cash: 145-160 µm. Jung: 145—180 µm. Hoogenraad and De Groot: 120—180 µm. My measurements: Length 117—236 µm.

Habitat: Sphagnum mosses. Not rare.

Remarks: The outline of the shell is often obscured by the diversity of diatom frustules incorporated into its structure. In some cases, the entire shell may appear as an amalgamation of diatoms. The siliceous materials used range from diatom frustules nearly equal in length to the body of the shell, to smaller frustules about 10 µm long, and spherical siliceous cysts from chrysomonad flagellates.

Penard (1890): “I have found this species only in Marstrand, Sweden, where it was abundant. Although it resembles Difflugia acuminata and one of Leidy’s illustrations appears to correspond to this form, it is certainly entirely distinct and should be considered a separate species. The shells, which I was only able to examine three months after my return from Sweden, were empty or contained a smooth cyst with a chitinous membrane.”

See the description of Penard,1902, at the bottom of this page.

Penard, 1902:
It closely resembles Difflugia pyriformis, it is true, but certain differences, particularly regarding the shape and structure of the shell, as well as the nucleus, clearly distinguish it, making it an easily identifiable species. The shell is composed of a thin yet rigid hyaline membrane, always covered with diatoms, mixed with some stones or fragments of a different nature. At the aperture, these elements are frequently replaced by very small round silica-shelled algae, forming a more or less regular ring. Regarding the general shape of the shell, it differs from Difflugia pyriformis mainly by having a more elongated neck that is narrower at the aperture. In sum, the shell always exhibits a unique appearance that is not found in Difflugia pyriformis, even when the latter incorporates diatoms. However, this distinctive appearance is difficult to describe precisely.
The cytoplasm does not completely fill the interior. It contains the usual elements—prey, bright granules, and a significant amount of oval starch grains—but never zoochlorellae. These symbiotic algae, which are common in typical Difflugia pyriformis, appear to be entirely absent in this species.
The nucleus is rarely visible in detail and is difficult to isolate. When attempting to crush the shell, which is quite resistant and flattens somewhat before breaking open, the nucleus is almost always compressed under the membrane and cannot escape. However, I managed to isolate two nuclei completely. Both measured 30 µm in diameter and possessed a clearly visible nuclear membrane. Surrounding this was a narrow margin of nuclear sap, followed by a zone of very flattened small nucleoli. In cross-section, these nucleoli appeared spindle-shaped and formed a thin, nearly continuous layer. The interior of this hollow sphere was filled with a clear plasma containing fine granules or dust-like particles. This type of nucleus is never found in Difflugia pyriformis, making it an important distinguishing feature of the species. Like many species inhabiting mosses and sphagnum, this Difflugia has a strong tendency to encyst. The cysts are perfectly spherical, with a smooth, hyaline membrane. Typically, their interior contains a mass of starch granules.

I have never found Difflugia bacillifera outside of sphagnum, where it is not always abundant. Levander collected it from a small mountain pond filled with mosses—perhaps sphagnum was also present there? I collected it in relatively large numbers from sphagnum in Lake Couches, above Morgins (Valais), in a somewhat distinct form. In this case, the shell had a long, very narrow neck and, in addition to some diatoms, was covered with a fine network of very small, grayish debris. The average length of Difflugia bacillifera is 158 µm, with little variation from this measurement.

When I first described this species in 1890, I mentioned under the name var. inflata a very broad and stocky, overall ovoid form, which shared only the diatom covering with the primary form. Today, I believe that this ovoid form has no real connection to Difflugia bacillifera and is instead more closely related to Difflugia elegans, as a distinct variety.