Marcia the Martian is Marvin the Martian's apprentice and niece. She only appeared in "Duck Dodgers Jr.", where she went up against Duck Dodgers and Plucky Duck. At the end she and Plucky decided to go off and play, while Marvin and Dodgers duke it out.
Marcia is about 5 years old. She enjoys playing with building blocks, and is a very fast speaker. She is playful, and loves making friends. She befriends Plucky Duck (despite him being considerably older, and biggest fan of Uncle's arch enemy Duck Dodgers.) She only appears in only one episode, but is well liked. Marcia is very girly. She wears a pink jumper, and trousers with a purple skirt and cone party hat that has a pink bow. She has sneakers which resembles her uncle's. She is supportive of her evil Uncle, simple reason she loves him. She is often mistaken for Marvin's daughter seeming as how she calls him "daddio" in the episode.
It is unknown whether Marvin has a brother or sister, because Marcia's parents aren't seen. It is still obvious that Marvin is the youngest of whatever siblings.
Her name, after considerable study, appears to be a corruption of the Koshallic name Ma'rwasth'eea, or "Female Spirit of the Double Moonrise". Strangely, she gained her adult name approximately eight Earth years before the general ceremony. However, given the somewhat eccentric nature of her family, it shouldn't be too difficult to allow for extenuating circumstances.