Ryūnosuke Stunned! Solid Rock Mother Cherishes Her Young Pebble!! (竜之介ボー然！わが子恋しや岩石の母！！, Ryūnosuke Bōzen! Waga Ko Koishi ya Ganseki no Haha!!) is the 123rd episode of Urusei Yatsura.
At a beach town, Cherry was tasked to search for a food-thieving goblin while Ataru and Mendō find a woman underwater who greets Ryūnosuke as her child and whom her father is convinced this is his long-lost Masako.
Differences from the manga
One scene was not included in the anime: Lum and Shinobu ask Cherry if he hasn't seen Ataru and Mendō who are peeping at girls underwater, and Cherry ask if they saw a monster, to which Shinobu answers "right here" while reflecting Cherry with a mirror.