Evidence against gastrointestinal pseudoparasitism by the land planarian, Bipalium kewense Moseley 1878.

The possibility of gastrointestinal pseudoparasitism by the free-living land planarian, Bipalium kewense, was tested by feeding and survival experiments. The intestinal tracts of three dogs were negative for B. kewense after the individual dogs were fed eight, three, and four large worms and autopsied at 12 h, 3 h, and 45 min, respectively. Survival of the worms in Warburg flasks, under N2, AT 27 C, was 2 h or less.. In Gas Pak jars (CO2 + H2) at 37 C, survival was less than 60 min. Aerobically, at 37 C, survival varied from 45 to 60 min. Attra-tion of the worms to stool material was examined by placing planaria inside square whose boundries were constructed of fecal smears. Bipalium kewense exposed to canine feces showed strong avoidance reactions. Urea, a nitrogen end product of these worms, was also shown to be a negative stimulus for B. kewense. Failure to establish even short term passage in the digestive tract, lethality of 37 C and anaerobic environments, and sensitivity to feces makes gastrointestinal pseudoparasitism unlikely in these organisms.