Body medium-sized; anterior end Genus *_Lembus_ produced into neck-like elongation

* Presence at Woods Hole indicated by asterisk.

Genus PLEURONEMA Dujardin '41.

(Perty '52; Clap. & Lach. '58; Stein '59, vol. I; Quennerstedt '67; Kent '81; Butschli '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 (Butschli) 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 ca.n.a.ls leading to it. A round macronucleus with one micronucleus is in the anterior half of the body. The a.n.u.s 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 cra.s.sa_ Dujardin '41; _P. marina_ Duj. '41; Fabre-Domergue '85; _P. coronata_ Kent '81; _Paramoecium chrysalis_ Ehr. '38; _Lembadion orale_ G. & R. '88; _Histiobalantium agile_ Stokes '85, '88.

The body is ovoid, slightly flattened, rounded at both ends, the anterior end sharper than the posterior. The ventral surface is almost entirely taken up by a peristome which extends from the anterior end posteriorly three-quarters of the body length. The posterior end of the peristome is straight, the left curved, following the depressed portion. The body is covered with fine cilia in longitudinal lines, except on the peristome. The mouth is small and situated in the hollow of the peristome near the left border. On the left peristome edge is a large undulating membrane. It begins near the anterior end of the body and increases in height posteriorly following the peristome edge around on the right side. This posterior bend of the membrane causes the appearance of a full sail, so often seen. It can be entirely withdrawn and folded together in the peristome. On the right edge of the peristome are large, powerful cilia. The contractile vacuole is central and dorsal; the macronucleus is in the anterior half of the body, with one attached micronucleus. Food consists of bacteria. Not very common. Fresh and salt water. It often remains quiet, with membrane and cilia outstretched, as though dead, but suddenly gives a spring and is gone.

[Ill.u.s.tration: Fig. 40.--_Pleuronema chrysalis_.]

Pleuronema setigera, n. sp. Fig. 41.

Body colorless, elongate, and with the general form of a cuc.u.mber, the posterior end being somewhat pointed. The mouth and relatively small peristome are situated in the lower third of the body. The peristome begins as a shallow furrow at the center of the ventral surface and dips sharply into the buccal depression, which is deep and turned toward the posterior end. The left edge of the peristome bears a high undulating membrane, which extends anteriorly only as far as the center of the body; posteriorly it pa.s.ses around to the right edge of the peristome, thus forming the characteristic membranous pocket. Inside the oral depression is a second undulating membrane, running down to the mouth. This is small and without an oesophagus. The body is clothed with long setose cilia which are frequently fully outstretched when the animal is resting, a slight tremor of the large membrane alone indicating vitality. Posteriorly these appendages are drawn out into long filiform setae, the number varying in different individuals from three to nine or ten. These are extremely fine and difficult to see without a high power (_e.g._ 1/12 oil) and careful focussing of the substage condensor. Like _P.

chrysalis_, the resting periods are terminated by sudden springs, otherwise the movements are steady and forward. The macronucleus is central, and the contractile vacuole posterior and terminal. Length 45 to 50; greatest diameter 17. In decaying algae.

It was this form, I believe, that Peck '95 described as a "ciliate."

[Ill.u.s.tration: Fig. 41.--_Pleuronema setigera_.]

Genus LEMBUS Cohn '66.

(Cohn '66; Quennerstedt '69; Kent '81; Fabre-Domergue '85; Gourret & Roeser '88; Butschli '88; Shevyakov '96.)

Free-swimming animals of elongate form, more or less elastic, and flexible, bending readily to avoid obstacles, etc. The anterior half is usually drawn out into a slightly curved neck-like portion. The peristome is a small groove leading from the anterior end to the mouth about midway down the ventral side of the body. Butschli, following Quennerstedt, describes an undulating membrane on each side of the peristome groove. Other observers, however, usually describe but one, the left, which is clearly defined and stretches out some distance from the body, while the right border is described as having smaller but very active cilia. The general body surface is clothed with fine, uniform cilia, and body striae are usually absent. One or more caudal bristles may be present. The contractile vacuole is posterior and terminal, and may be multiple. The macronucleus is spherical and perhaps double (Kent). Food is chiefly bacteria, and the animals are frequently found with the anterior end embedded in zoogloea ma.s.ses. Salt water, usually in infusions.

Lembus infusionum, n. sp. Fig. 42.

The body is elongate, lancet-shaped, with a tapering anterior extremity. The dorsal outline is concave through the bending of the anterior end, while the ventral outline presents an even, convex curve. The mouth lies slightly above the center of the body and marks the posterior limit of the ventral peristomial groove, which curves slightly from the anterior extremity. Each side of this groove bears an undulating membrane, the left being much larger and conspicuously striated. The general form of this left membrane is triangular, the widest part is anterior, the narrowest at the mouth. The right membrane is similar in form, but smaller and more active.

The endoplasm is colorless and finely granular, not regionally differentiated. The ectoplasm consists of a relatively thick cortical plasm specially noticeable in the posterior half of the body and a delicate cuticle which bears almost imperceptible longitudinal markings--the insertion points of the fine cilia. The body is covered with uniform cilia except at the anterior extremity. Here they are much larger and bristle-like. I was unable to find any cilia in the peristome. One long caudal bristle, one-quarter of the length of the body, trails out behind. The macronucleus is spheroidal and placed near the center of the body; a conspicuous micronucleus lies near it.

A row of contractile vacuoles extends from the posterior end. I have seen as many as six of nearly equal size and one or two smaller ones.

The intervals of contraction are quite long. Length 70 to 75; greatest diameter 10 to 12.

_L. infusionum_ resembles _L. elongatus_ in its general form and in its mode of life, for it excavates a retreat in zoogloea ma.s.ses and lies there for considerable periods perfectly quiet. It differs from _L. elongatus_ and from _L. velifer_ (probably the same as _L.

elongatus_ of Claparede & Lachmann) in the presence of the caudal bristle, in the absence of annular markings, number of contractile vacuoles, and in the slightly smaller size. It resembles _Lembus verminus_ (Muller) as described by Kent (_Proboscella vermina_), and _L. intermedius_ as described by Gourret & Roeser (_Lembus verminus_ syn.)in the absence of annular markings and in the presence of a caudal bristle. It differs from the former, however, in the absence of a tentacle-like process, and from both in the absence of a double nucleus and in the presence of many vacuoles. These features are so characteristic of all the specimens examined that I have concluded, somewhat reluctantly, to give it a specific name. It is common in old infusions of algae, especially after decomposition is well advanced.

Its food consists of bacteria.

[Ill.u.s.tration: Fig. 42.--_Lembus infusionum_.]

Lembus pusillus Quennerstedt 1869. Fig. 43.

Synonym: _L. subulatus_ Kent 81.

This species is much smaller than the preceding, and might easily be mistaken for _Uronema marina_. It is subcylindrical in form, the anterior end bluntly pointed, the posterior end rounded. The oral apparatus is quite different from _Uronema_. The mouth, as in the preceding species, is at the end of a long peristomial groove extending from the anterior end to the middle of the body. The edges of the peristome bear undulating membranes as in _L. infusionum_.

Like the latter, there is one caudal bristle, but unlike it there is only one posterior contractile vacuole, while the endoplasm is filled with large granules or food b.a.l.l.s. The cuticle is distinctly striated with longitudinal markings, and the cilia are uniform in length.

Habitat similar to that of _L. infusionum_, in zoogloea ma.s.ses.

Length 26 to 30; diameter 7 to 8.

Although Quennerstedt's description of _L. pusillus_ makes no mention of a caudal bristle, the size and other characters are so closely similar that I hesitate to make a new species. The bristle is extremely delicate, scarcely thicker than a cilium, and easily overlooked, yet with proper focussing of the condenser I found it on every specimen examined.

[Ill.u.s.tration: Fig. 43.--_Lembus pusillus_.]

KEY TO MARINE GENERA OF OPALINIDae.

Diagnostic characters: The form is oval, and the body may be short or drawn out to resemble a worm. They are characterized mainly by the absence of mouth and pharynx.

Anterior end not pointed; body Genus *_Anoplophrya_ cylindrical; tapering

Anterior end pointed; body elongate; Genus _Opalinopsis_ cylindrical; tapering

* Presence at Woods Hole indicated by asterisk.

Genus ANOPLOPHRYA Stein '60.

(Stein '60; Claparede '60; Leidy '77; Vejdovsky '79; Kent '81; Balbiani '85; Butschli '88; Shevyakov '96.)

The general form is elongate, cylindrical or slightly flattened, with rounded ends, the posterior end tapering. The body is striated with clearly defined, often depressed lines, which run longitudinally and sometimes spirally. The contractile vacuoles are usually placed in rows upon the edges. The macronucleus is almost always long and band-formed, rarely oval, and generally extending through the entire length of the body. Micronuclei have been made out in one case.

Reproduction is effected by simple cross division or by budding at the posterior end, and is frequently combined with chain formation.

The main characteristic is the entire absence of mouth and oesophagus, the animals being parasitic in the digestive tract of various annelids. Parasites, salt-water forms.

Anoplophrya branchiarum. Stein '52. Fig. 44.

_A. circulans_ Balbiani.

The body is cylindrical to pyriform, in the latter case broadened anteriorly. Cuticle distinctly marked by longitudinal striations which take the form of depressions and give to the body a characteristic melon shape. The endoplasm contains a number of large refringent granules--probably body products. The nucleus is elongate, somewhat curved, and coa.r.s.ely granular. A micronucleus lies in the concavity. The cilia are long, inserted rather widely apart along the longitudinal markings. The contractile vacuole is single and is located at the pointed end, which is directed backwards during locomotion. One specimen found free swimming among some algae.