The tribe of Levi included the clans of the Gershonites, Kohathites, Merarites,
Levi was the father of Gershon, Kohath, and Merari.
Aaron's son Eleazar married one of Putiel's daughters, and their son was Phinehas. This ends the list of those who were the heads of clans in the Levi tribe.
But those from the Levi tribe were not included
The only Israelites not included were the Levites, just as the LORD had commanded Moses.
“Now I want you to count the men and boys in the Levi tribe by families and by clans. Include every one at least a month old.”
Levi's three sons, Gershon, Kohath, and Merari, had become the heads of their own clans.