The ethogram of Euplotes crassus (ciliata, hypotrichida): I. The wild type.

The behavior of Euplotes crassus has been studied qualitatively and quantitatively in an attempt of throwing new light onto the problem of the relationships occurring among motor behavior, systematic position and evolutionary strategies of the ciliated protozoa. It was found that both single and paired Euplotes creep along piecewise pathways whose geometric elements (arcs, segments, angles) have been measured. E. crassus performs different delicate maneuvers to shift from one element of its trajectory to the next: beyond the Continuous Trajectory Change, the Smooth Trajectory Change and the Rough Trajectory Change, described elsewhere for other ciliates, three different kinds of Side-Stepping Reaction were recognized and carefully described. The average velocity is 850 μm/sec during creeping and 800 μm/sec during swimming. Finally, also the mating behavior has been analyzed and the successive steps leading to pair formation thoroughly described. The data are compared with those already available for different species.