Key to marine genera of Chiliferidæ.
Diagnostic characters: Mouth never lies behind the middle of the body; the œsophagus is but slightly developed. The undulating membranes are placed either on the edge of the mouth or in the œsophagus. A peristomial depression leading to the mouth is absent or very slightly indicated.
1. Mouth in the anterior half, undulating membrane on left edge only; right edge continued in a long ventral furrow Genus *[Frontonia]
2. Two undulating membranes; mouth central; no caudal bristles Genus *[Colpidium]
3. Two undulating membranes; caudal bristle Genus *[Uronema]
* Presence at Woods Hole indicated by asterisk.

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

(Ehrenberg, subgenus of Bursaria '38; Claparède & Lachmann '58;
Bütschli '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 (Bütschli). The œsophagus 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 canals radiating throughout the endoplasm. The macronucleus is oval and centrally placed. Micronuclei vary from one to many. An anal 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 mass 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.


Fig. 37.—
Frontonia leucas.
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