Final answer:
The ancestral nematode was most likely free-living.
Step-by-step explanation:
The ancestral nematode, based on the study mentioned in the introduction, was most likely free-living. Nematodes are a phylum that includes both free-living and parasitic organisms. While some nematodes are parasites, it is important to note that not all nematodes are parasitic. Therefore, based on the available information, the ancestral nematode was most likely free-living.