[Ill.u.s.tration: Fig. 49.--_Peritromus emmae_, ventral and lateral aspects.]

KEY TO THE MARINE GENERA OF OXYTRICHIDae.

Diagnostic characters: The peristome is not always marked off from the frontal area. In the most primitive forms the cilia on the ventral surface are similar to those of the preceding family (_Peritromidae_). Usually some of the anterior and some of the posterior cilia are fused into cirri, distinguished as the frontal and a.n.a.l cirri, respectively. In the majority of forms all of the cilia are thus differentiated; strong marginal cirri are formed in perfect rows, and ventral cirri in imperfect rows. In addition to the adoral zone there is an undulating membrane on the right side of the peristome, and in some cases a row of cilia between the membrane and the adoral zone. These are the par-oral cilia and they form the par-oral zone.

1. The posterior end is pointed or 2 tail-like

The posterior end is rounded; 5 not tail-like

2. The front end is pointed 3

The front end is rounded 4

3. Frontal and a.n.a.l cirri absent; Genus _Stichotricha_ often tube-forming

Eight frontal and 3 caudal cirri; Genus _Gonostomum_ not tubiculous

4. a.n.a.l cirri present; with or Genus *_Epiclintes_ without short lateral bristles

a.n.a.l cirri absent; no bristles Genus _Uroleptus_

5. With frontal cirri 6

No frontal cirri; 2 to 3 rows of Genus _Holosticha_ ventral cirri; a.n.a.l cirri small

6. Right margin of peristome straight Genus _Oxytricha_ as far as the anterior end; 5 rows ventral cirri; 5 a.n.a.l cirri

Right margin of peristome curved 7

7. Five rows or less of ventral cirri 8

More than 5 rows of ventral cirri Genus _Urostyla_

8. Membranelles normal; 5-10 a.n.a.l Genus *_Amphisia_ cirri; no caudal cirri

Membranelles normal; 5 to 10 a.n.a.l Genus _Stylonychia_ cirri; 3 caudal cirri

Membranelles very large and Genus _Actinotricha_ powerful; adoral zone not continued to mouth; 5 a.n.a.l cirri

* Presence at Woods Hole indicated by asterisk.

Genus EPICLINTES Stein '62.

(Stein '62, '64, '67; Mereschowsky '79; Gruber '87; Butschli '88.)

Very active, contractile, colorless forms of rather small size. In the fully expanded condition the body is oval and long, with its greatest width in the center or at the front half of the body. The posterior end is always drawn out into a relatively long tail, which is extremely elastic. The peristome is short and stretches around the front end of the animal. In the frontal region are from one to three rows of cirri. The ventral surface is covered with longitudinal rows of cilia, the number of rows being in dispute (6 to 7 according to Stein; 9 according to Mereschowsky and Rees) Some of these cilia project from the lateral edges and from the posterior end, where they are slightly elongated. The a.n.u.s is dorsal and placed at the beginning of the posterior process. Macronucleus probably double.

Movement is rapid and restless, the tail process contracting to jerk the body backward. Salt water.

Epiclintes radiosa Quenn. Fig. 50.

Synonym: _Metra radiosa_ Quenn.

The body is elongate, slightly narrowed anteriorly, and drawn out posteriorly into a long, retractile, tail-like portion. Five large cirri extend outward from the anterior extremity. The caudal portion may be extended to a distance equal to twice the length of the body or contracted to half the length. The peculiar nervousness of this form made it extremely difficult to study, and the oral region was imperfectly made out. The anterior cirri appear to line the upper left border of the peristome, which is marked by a row of large cilia. The peristome begins upon the right side of the anterior end and pa.s.ses backward and to the left, narrowing at this point. The mouth is very small and difficult to see. It is apt to stay in one locality under zoogloea, switching back and forth with great vivacity, or hanging on by the posterior cilia while the anterior end stretches out in the surrounding medium. Nucleus and contractile vacuole were not observed. Length 45.

[Ill.u.s.tration: Fig. 50.--_Epiclintes radiosa_.]

Genus AMPHISIA Sterki '78.

(Sterki '78; Kent '81; Butschli '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 a.n.a.l 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_ Muller; _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 a.n.a.l 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 135; greatest width 40.

[Ill.u.s.tration: Fig. 51.--_Amphisia kessleri_.]

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.

KEY TO THE MARINE GENERA OF EUPLOTIDae.

Diagnostic characters: Cilia, as well as the frontal, marginal, and ventral cirri, very much reduced; the a.n.a.l cirri, on the other hand, are always present. The macronucleus is band-form.

1. Frontal cirri more than 8 2

Frontal cirri less than 8 3

2. Eleven marginal cirri on the left Genus _Certesia_ side; 11 frontal cirri

Four marginal cirri, 2 on each Genus *_Euplotes_ side; 9 to 10 frontal cirri

3. Seven frontal, 5 a.n.a.l, 3 right Genus *_Diophrys_ marginal, and 2 left marginal cirri