Genus AMPHISIA Sterki '78.

(Sterki '78; Kent '81; Bütschli '88.)

The body is plastic and soft, colorless or slightly tinged with yellow or red. In form it is oval or elongate, the posterior end is rounded and slightly reduced in diameter, but does not form a distinct tail. The anterior end is also rounded and similarly reduced in width. There are two rows of marginal cirri (Randcirren), which may be placed some distance from the edge, and two or three rows of ventral cirri between them. There are from 3 to 5 frontal cirri of larger size than those of the ventral rows, and from 5 to 10 anal cirri. (The genus Holosticha is similar in all respects save the presence of frontal cirri.) The macronucleus is double; the contractile vacuole is central and on the left side. The peristome is long and rather narrow and carries an undulating membrane on its right margin. Fresh and salt water.

Amphisia kessleri Wrzes. '77. Fig. 51.

Synonyms: Trichoda gibba Müller; Oxytricha gibba Stein '59; O. velox? Quen. '69; O. kessleri Wrzes. '77.

Body elongate, slightly sigmoid and swollen in the center, about 3-1/2 times as long as broad; the rounded anterior end is turned to the left, the similarly rounded posterior end to the right; both ends taper slightly. The peristome is long and narrow, with a distinct adoral zone which appears broken in its course. To the right of this adoral zone is a single line of preoral cilia. On the right border of the peristome is an undulating membrane. The three frontal cirri form a triangle and the five smaller anal cirri form a continuous line with the broken row of ventral cirri. There are two and one-half rows of ventral cirri and the marginal cirri are drawn in until they are ventral in position.

Length 135µ; greatest width 40µ.


Fig. 51.—Amphisia kessleri.
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This variety differs from O. kessleri as described by Wrzesniowski in having three frontal cirri instead of four. Another difference is in the structure of the nuclei and in their position. These differences are too minute to warrant a specific name. O. velox of Quennerstedt is probably the same as 0. kessleri, but differs in having three complete rows of ventral cirri. O. velox has three frontal cirri in a line, thus differing from the Woods Hole form.