Spinitectus macrospinosus n. sp., a parasite of the channel catfish Ictalurus punctatus, from the Red and Assiniboine rivers in southern Manitoba, Canada, is characterized by spines reaching a maximum length of 21.8-26.8 microm (means for males and females, respectively) in the anterior esophageal region, arranged in 4 sectors in the anterior region of the body. Spines in this region of the body increase in size and decrease in number (from a maximum of 6 to 3 per sector). The combination of spine length, number, and arrangement and the position of the excretory pore (between spine rows 6 and 7) readily distinguishes it from all its North American congeners, including the species it is most similar to, S. carolini. It is different from S. gracilis and S. acipenseri in having a posteriorly directed vagina, an excretory pore between spine rows 6 and 7, a longer stoma, a right spicule with a terminal ventral barb, and a heart-shaped caudal mucron. Spinitectus macrospinosus is similar to other North American species of Spinitectus, e.g., S. carolini, S. micracanthus, S. mexicanus, S. osorioi, and S. humbertoi, in having the anterior rows of spines arranged in 4 sectors. It is also similar to S. micracanthus and S. carolini in possessing a relatively long stoma, a posteriorly directed vagina, a right spicule with a terminal ventral barb, and a heart-shaped caudal mucron. Furthermore, it is similar to S. carolini in possessing an "area rugosa" with 2 rows of precloacal cuticular cleats. In southern Manitoba, S. macrospinosus appears to mature only in the channel catfish. Reexamination of museum specimens revealed that the nematode also is found in I. furcatus in Kentucky Lake (Kentucky-Tennessee) and in I. lacustris in Lake Texoma (Oklahoma-Texas).