Part 16 (1/2)

[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.