Hermodice carunculata, a tropical polychaete, was collected along the southern coast of Puerto Rico during April through July 1969. The intestinal contents of the worms were examined and a holotrichous ciliate was found. Ninety-one percent of 121 freshly collected worms harbored the ciliate. Only 35% of 44 worms carried the protozoan when they were maintained in the laboratory longer than three days. The ciliate is pyriform, dorsoventrally flattened and its size ranged from 40.95µ x 34.58µ to 72. 80µ x 45. 50µ.