Prithu’s son was Antardhana, his son was Havirdhana. Havirdhana’s son was Prachinavarhi. He married Savarna, the daughter of the ocean.
Their sons were the Prachetas. They meditated on the bottom of the ocean, refusing their duty to populate the earth. The moon finally managed to convince them to marry Marisha and do their job.
The story of the Prachetas is told in variations in the Puranas, most extensively in Vishnu and Vayu Purana.
https://www.astrojyoti.com/vishnupurana.htm
https://www.astrojyoti.com/vayupurana.htm