Euplotes affinis is a very common hypotrichous ciliate, which is easy to overlook in fresh samples due to its small size. However, it likes to settle on the floating coverslip and is also frequently found near the surface of old samples.

A characteristic feature is the spread-out, separate left marginal cirrus, which stands out due to the otherwise greatly reduced cilia (s. fig. 2 a). Of the total of 9 frontoventral cirri, two are clearly separated on the right margin of the body (s. fig. 2 b). Longitudinal ribs are located between the strong transverse cirri (s. fig. 2 b). The dorsal side is convexly curved and also has ribs (s. fig. 4). Between the dorsal ribs are rows of short, bristle-like cilia, which can only be seen under high magnification in squashed specimens (s. fig. 5). The macronucleus is C-shaped, which can also only be seen in squashed specimens. The micronucleus is often found at one end of the macronucleus, but is difficult to see as it can often be very hyaline (s. fig. 6).