(Cl. et Lach. '58; Entz '84; Mobius '88; Shevyakov '96.)

Small forms, firm in outline, and colorless or slightly colored. The body is somewhat clam-shaped, flattened, slightly curved or straight on the right side, the other more convex. The true ventral side is only a narrow strip along the right and anterior edge of the body, the apparent ventral side being a fold of the very large dorsal surface which comes around ventrally, forming a valved structure somewhat a.n.a.logous to a clam sh.e.l.l. Cilia are limited to the outer edge of the small ventral surface, which also bears a peculiar spine at the posterior end. Behind this spine are larger cilia. The mouth opening lies in the anterior widened portion of the ventral surface and is connected with a smooth tubular pharynx. The right half of the dorsal side, _i.e._, the apparent dorsal side, is arched and bears longitudinal ridges. Two to four contractile vacuoles are placed on the ventral side. The macronucleus is usually dorsal, elliptical, and cleft, with one micronucleus attached. Fresh and salt water.

Dysteria lanceolata Cl. et Lach. Fig. 36.

Synonym: _Cypridium lanceolatum_ Kent '81.

Outline of the flattened body ovoid; body consists of two valve-like portions; the edge of the right valve is nearly straight, that of the left valve more or less sinuous; anteriorly it is cut away, obliquely and posteriorly it has a deep indentation in which the seizing spine rests. The cilia are confined to the ventral surface, here reaching, however, from the anterior dorsal extremity to below the posterior indentation. Posteriorly the cilia become larger, corresponding to the larger cirri of _D. armata_, which are posterior to the spine.

The mouth lies between the two valves and is surrounded by a long and smooth buccal armature which pa.s.ses downward and backward to the left a distance equal to about half the entire body length. The macronucleus is situated in the dorsal region in the central part of the body. There are two contractile vacuoles, one behind the center of the buccal armature, the other near the inner end of this organ.

Movement is in circles, the animal moving around quite rapidly when not attached by its posterior process. It is colorless and measures 45 in length by 27 in width. Claparede & Lachmann and Shevyakov describe it as 70 long.

[Ill.u.s.tration: Fig. 36.--_Dysteria lanceolata_.]

KEY TO MARINE GENERA OF CHILIFERIDae.

Diagnostic characters: Mouth never lies behind the middle of the body; the oesophagus is but slightly developed. The undulating membranes are placed either on the edge of the mouth or in the oesophagus. A peristomial depression leading to the mouth is absent or very slightly indicated.

1. Mouth in the anterior half, Genus *_Frontonia_ undulating membrane on left edge only; right edge continued in a long ventral furrow

2. Two undulating membranes; mouth Genus *_Colpidium_ central; no caudal bristles

3. Two undulating membranes; caudal Genus *_Uronema_ bristle

Genus FRONTONIA Ehr. (Cl. & Lach. '58?).

(Ehrenberg, subgenus of _Bursaria_ '38; Claparede & Lachmann '58; Butschli '88; Shevyakov '96.)

Form elongate and cylindrical, or often flattened dorso-ventrally, with round or pointed ends. It is usually plastic and contractile.

Cilia are evenly distributed about the body and are similar in length. The large, open mouth lies on the anterior half of the ventral surface, and is elongate and oval in outline. On its left edge is a well-defined membrane which stretches across to the right side of the mouth. On the right edge is a small, longitudinally striped tract which is free from trichocysts and smooth in appearance. This tract is continued posteriorly in a long furrow, which in some cases reaches the posterior end of the animal. A few rows of cilia in this furrow vibrate differently from the others and give the effect of a membrane (Butschli). The oesophagus is extremely short and hard to make out. The body is usually covered uniformly with trichocysts, often of considerable size. There are 1 or 2 vacuoles with long ca.n.a.ls radiating throughout the endoplasm. The macronucleus is oval and centrally placed. Micronuclei vary from one to many. An a.n.a.l opening is placed at the end of the long ventral furrow. The plasm is colorless or green by the presence of Zoochlorella, or colored brown or black by pigments. In these cases there is a considerable pigment ma.s.s on the anterior end. Movement is regular, forward, and combined with rotation. Food consists of foreign objects, diatoms, other protozoa and the like. Fresh and salt water.

Frontonia leucas Ehr. Fig. 37.

Synonyms: _Frontonia vernalis_ Ehr. '38; _Bursaria leucas_ Allman '55, Carter '56; _Panophrys leucas_ Duj. '41, Stein '67; _Panophrys vernalis_ Dujardin '41, Stein '67; _P. chrysalis_ Duj. '41, Fromentel '74; _Cyrtostomum leucas_ Stein '67, Kent '81.

Form ovoid, elongate, occasionally a little flattened dorso-ventrally. Mouth in the anterior third of the body. The left edge of the mouth carries a distinct undulating membrane; the right edge is plain, longitudinally striated and bears cilia. It is slightly depressed and the depression is carried posteriorly in the form of a shallow furrow which reaches to the posterior end. The contractile vacuole is on the left side, the spheroidal nucleus on the right side of the furrow. The body is uniformly covered with fine cilia, and the periphery is uniformly studded with large trichocysts, except along the furrow. Food consists of dinoflagellates and other small forms. Color dark brown to black.

Length 330; width 200.

This form differs considerably from the fresh-water _Frontonia leucas_ as described by Schewiakoff '89, especially in the extreme length of the peristomial furrow, in the position of the nucleus and contractile vacuole, and in the nature of the water ca.n.a.ls. These in the Woods Hole form are very irregular in size and very much branched, not uniform as in Lieberkuhn's (see Butschli) figure of _Frontonia leucas_, nor radiating as in Schewiakoff's description.

This may be the same species as _Frontonia marina_, of Fabre-Domergue '91, whose description and figure I have not seen.

[Ill.u.s.tration: Fig. 37.--_Frontonia Leucas_.]

Genus COLPIDIUM Stein '60

(Butschli '88; Maupas '83.)

The general form is oval, slightly compressed laterally with the dorsal side strongly arched. The ventral side is slightly incurved.

The anterior end is somewhat smaller than the posterior end, which is broadly rounded. The mouth is placed some distance from the anterior end in an oral depression and opens into a tubular oesophagus. There are usually two undulating membranes which do not extend beyond the mouth borders. The right undulating membrane extends down into the oesophagus and appears to be attached to the walls of the latter. The body stripes in front of the mouth are twisted to the left. The a.n.u.s is terminal and the contractile vacuole may be terminal or situated forwards in the dorsal region. The macronucleus is spherical and has one micronucleus attached. Food consists mainly of bacteria.

Movement rapid, but interrupted.

Fresh and salt water, common in infusions.

Colpidium colpoda Ehr., sp. Fig. 38.

Synonyms: _Colpidium cucullus_ Kent '81; _C. striatus_ Stokes '85; _Kolpoda cucullus_ Duj. '41; _Paramoecium colpoda_ Ehr. '38, Quennerstedt '67; _Plagyiopyla nasula_ Kent '81, G. & R. '86; _Glaucoma pyriformis_ G. & R. '86; _Tillina campyla_ Stokes '85, '88.

The body is oval, somewhat larger posteriorly, and a little compressed dorso-ventrally. The anterior end is twisted a little from the right to the left (more evident in fresh-water forms), and leans somewhat toward the ventral side. Under this portion, on the ventral side, lies the mouth in a large depression just above the middle of the body. The entire body is covered with uniform and delicate cilia, which are placed in longitudinal rows. These rows are almost straight on the dorsal side, but bend on the ventral surface, following the contour of the twisted anterior portion. The endoplasm is finely granular; the oesophagus leading into it is very distinct.

Schewiakoff ('89) describes two membranes, an inner and an outer; Maupas ('83) describes them as right and left. In the present species I was able to make out only one. The macronucleus is central, spherical in form, and bears a single minute micronucleus. The contractile vacuole is posterior and dorsal to the long axis of the body. The a.n.u.s is ventral to this axis and also posterior. Length 45, width 20. Common.

This marine variety is much smaller than the fresh-water form and the form differs in a number of respects, viz, in the anterior torsion and in the structure of the mouth. These may be, however, only individual variations of a widely spread species, and I believe it is perfectly safe to describe this as _Colpidium colpoda_.

[Ill.u.s.tration: Fig. 38.--_Colpidium colpoda_.]

Genus URONEMA Duj. '41.

(Quennerstedt '69; Cohn '66; Kent '81; Butschli '81; Schewiakoff '89; Shevyakov '96.)

Minute forms; colorless and constant in body form. The form is oval, slightly compressed on the ventral side, while the dorsal side is distinctly arched. The membrane is distinctly marked by rather widely separated striae. These occasionally have a spiral course about the body; in all cases they can be easily counted. The mouth is large and placed near the center of the ventral surface. It is sometimes approached by a very shallow depression or peristome from the anterior end, and marked by two rows of cilia. An undulating membrane extends down the mouth. Oesophagus absent. A long, stiff bristle extends outwards from the posterior end. The contractile vacuole is terminal or subterminal and near the a.n.a.l opening. The macronucleus is spherical, centrally placed, and with one micronucleus closely applied. Movement is rapid and usual forwards in a straight line, often found resting, however, with outstretched cilia in contact with some foreign body. Food mainly bacteria. Fresh and salt.w.a.ter, usually in decomposing vegetable substances.

Uronema marina Duj. Fig. 39.

Synonyms: _Enchelys triquetra_ Dujardin; _E. corrugata_ Duj.; _Cryptochilum griseolum_ Maupas '83; _Philaster digitiformis_ Fabre-Domergue '85.

Small animals with ellipsoidal form and about twice as long as broad. The mouth lies in the upper half of the body and bears a well-developed undulating membrane upon its left edge. The membrane is longitudinally striped and covered with long and vibratile cilia.

The right edge of the mouth bears cilia which are about the same in size as the body cilia, but are more closely inserted (Schewiakoff).

The most characteristic feature is the long caudal bristle, which is extremely delicate and about two-thirds the length of the body.

Schewiakoff thinks this bristle has a sensory function. I could not make this out, for although other protozoa ran against this bristle, often bending it well over to one side, the animal showed no sign of irritability but lay quiescent. A spherical macronucleus with attached micronucleus lies in the center of the body. The contractile vacuole is posterior in front of the bristle. The macronucleus was found to be double, as though just divided, in a large percentage of cases. This may be a precocious division of the nucleus long before signs of the body division are evident. Such a phenomenon, however, is rare, the macronucleus usually dividing at a late stage of cell division. Length 30 to 50; width 15 to 20. Common in decomposing algae.

[Ill.u.s.tration: FIG. 39.--_Uronema marina_.]

KEY TO MARINE GENERA OF PLEURONEMIDae.

Diagnostic characters: The mouth is at the end of a long peristome running along the ventral side; the body is dorso-ventrally or laterally compressed. The entire left edge of the peristome is provided with an undulating membrane which occasionally runs around the posterior end of the peristome to form a "pocket" leading to the mouth. The right edge of the peristome is provided with a less-developed membrane. There may or may not be a well-developed pharynx.

Body small; not produced into Genus *_Pleuronema_ neck-like elongation