Key to marine genera of Chlamydodontidæ.
Diagnostic characters: Form usually ellipsoid, never very elongate. Transverse section of body circular or elliptical. The mouth is usually some distance from the anterior end and may be in the posterior part. Sometimes it is in the center of the ventral surface, again on the right side. The œsophagus invariably has a well-developed buccal armature, or a smooth peculiarly built œsophageal tube. Food particles of large size.
1. Body cylindrical. Cilia about entire body Genus *[Nassula]
Body flat 2
2. a. Without a caudal process 3
b. With a caudal process 5
3. a. Anterior end angular 4
b. Anterior end rounded Genus Chlamydodon
4. a. Dorsal striæ and cilia present, ventral cilia longer Genus Orthodon
b. Dorsal striæ and cilia absent; posterior end not pointed Genus *[Chilodon]
c. Dorsal striæ and cilia absent; posterior end pointed Genus Scaphidiodon
5. a. Caudal spine with posterior bristle-like cilia 6
b. Caudal spine without posterior bristle-like cilia; ventral cilia reduced Genus Trochilia
6. a. With pigment spot on anterior angle Genus Ægyria
b. Without such pigment spot Genus Onychodactylus
c. Cilia on right edge only of greatly reduced ventral surface Genus *[Dysteria]
* Presence at Woods Hole indicated by asterisk.

Genus NASSULA Ehr. '33

(Dujardin '41; Stein '67; Cienkowsky '55; Cohn '66; Clap. et Lach. '58;
Kent '81; Maupas '83; Entz '84; Fabre-Domergue '88; Bütschli '88; Shevyakov '96.)

The body is ovoid or cylindrical, with well-rounded ends, and in some cases slightly flattened. The mouth is ventral and placed some distance from anterior end (1/4 to 1/3 total length). A slight depression on the ventral surface marks the mouth region, which is further indicated by larger and more powerful cilia. The rest of the body is uniformly ciliated. The entire body is marked by clearly defined spiral stripes. The mouth is circular and the œsophagus is supported by a considerable armature, which usually extends dorsally and to the left, rarely to the right. In some cases the structure of this armature is indistinct; again it can be clearly seen to consist of definite rods (Stäbchen). The anus is probably always terminal. Contractile vacuoles are variable in different species. In some cases there is but one, which is placed at the posterior end or centrally on the ventral side; in others there may be four—two dorsal and two ventral. In many cases trichocysts are uniformly distributed. Sometimes the body is colorless; again, and more often, it is brightly colored with red, blue, brown, or black pigment. The macronucleus is globular and central, occasionally band-form and with numerous attached micronuclei. Food substance varied, usually vegetable matter, see, however, below. Cysts are globular. Movement is a steady progression, combined with rolling.

Nassula microstoma Cohn '66. Fig. 34.

Synonyms: Paramœcium microstomum Cl. et Lach. '58, Gourret et Roeser '88; Isotricha microstomum Kent '81.


Fig. 34.—Nassula microstoma.
[ ENLARGE ]