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 anal 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 anal cirri absent; Genus Stichotricha
   often tube-forming

   Eight frontal and 3 caudal cirri; Genus Gonostomum
   not tubiculous

4.  Anal cirri present; with or Genus *_Epiclintes_
   without short lateral bristles

   Anal cirri absent; no bristles Genus Uroleptus

5.  With frontal cirri 6

   No frontal cirri; 2 to 3 rows of Genus Holosticha
   ventral cirri; anal cirri small

6.  Right margin of peristome straight Genus Oxytricha
   as far as the anterior end; 5 rows
   ventral cirri; 5 anal 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 anal Genus *_Amphisia_
   cirri; no caudal cirri

   Membranelles normal; 5 to 10 anal Genus Stylonychia
   cirri; 3 caudal cirri

   Membranelles very large and Genus Actinotricha
   powerful; adoral zone not
   continued to mouth; 5 anal cirri

   * Presence at Woods Hole indicated by asterisk.

Genus EPICLINTES Stein ’62.

(Stein ’62, ’64, ’67; Mereschowsky ’79; Gruber ’87; Buetschli ’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 anus 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.