Read Numbers 3:20 Using Other Translations
And the sons of Merari by their families; Mahli, and Mushi. These are the families of the Levites according to the house of their fathers.
And the sons of Merari by their clans: Mahli and Mushi. These are the clans of the Levites, by their fathers' houses.
The clans descended from Merari were named after two of his descendants, Mahli and Mushi. These were the Levite clans, listed according to their family groups.