Both ciliates belong to the class Gymnostomea, which have an anterior mouth at or near the surface; it's supported but not constrained by trichites—internal rod-like structures—and can stretch greatly to accommodate large prey. The nucleus of both is polyploid, but the Haptorida (Dileptus) have toxicysts around the mouth, and the Pleurostomidae (Litonotus) do not. Both have long, flattened necks and relatively large bodies.
Litonotus' cytostome is a long slit; it has a prominent posterior water-expelling vesicle, a smooth pellicle, and it's typically 75-150 µm long.
Just as Litonotus draws even, Dileptus' neck reaches out. It conforms itself to the curve of Litonotus' body. The contact between the organisms is delicate as a caress,