(Perty '52; Clap. & Lach. '58; Stein '59, vol. I; Quennerstedt '67;
Kent '81; Bütschli '88; Schewiakoff '89; Shevyakov '96.)

Small to medium-sized ciliates, with an unchanging form. They are
somewhat lens-shape and laterally compressed, the two surfaces
about equally arched. The ventral surface is nearly straight or
but slightly arched; the dorsal is quite convex. The anterior and
posterior extremities are equally rounded. The peristome begins as
a small depression, but becomes larger until it takes in nearly all
of the ventral surface. The depression becomes much deeper at about
the center of the body, and is especially marked on the left side of
the peristome. In this deeper portion is the mouth, with an almost
imperceptible oesophagus. Upon the left edge of the peristome is a
high, undulating membrane, sail-like in appearance when extended.
This may stretch around the posterior edge of the peristome and upon
the right aide, thus forming a pocket by means of which the food
particles are directed into the mouth. The rest of the right edge
of the peristome is occupied by closely approximated powerful cilia
(Bütschli) or a second undulating membrane (Stein). The body cilia
are relatively long. Trichocysts and caudal bristles may be present.
The contractile vacuole is subterminal and dorsal; it is questionable
whether there are canals leading to it. A round macronucleus with
one micronucleus is in the anterior half of the body. The anus is
terminal. Food is chiefly bacteria. Movement combines springing with
swimming and rotation. Fresh and salt water.


Pleuronema chrysalis Ehr., sp. Fig. 40.

Synonyms: _Pleuronema crassa_ Dujardin '41; _P. marina_ Duj. '41;