The affix ḍhak comes optionally in the sense of a descendant after the word maṇḍūka as well as the affix aṇ,
Thus we get three forms, मण्डुक + ढक् = मांडूकेयः; मंडूक + अण् = मांण्डूकः; मण्डूक + इञ् = माण्डुकिः ॥,
ठक् च मण्डूकात्
Adhyāya 4 · Pāda 1 · Rule 119