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; 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 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 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.
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 330µ; width 200µ.
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 canals. These
in the Woods Hole form are very irregular in size and very much
branched, not uniform as in Lieberkühn's (see Bütschli) 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.
[Illustration: Fig. 37.--_Frontonia Leucas_.]