subitaneous
Sudden; suddenly done or made.
obsolete
Immediately developing (as contrasted with e.g. diapausing).
... subitaneous (immediately developing) and diapausing (dormant) eggs, brood retention, environmental sex determination and suppression of meiosis in subitaneous eggs. The production of subitaneous and diapausing eggs is[…]
Where it comes from
From Latin subitaneus. Doublet of sudden.
Adapted from the Wiktionary entry subitaneous (CC BY-SA 4.0).