Hoshi no Ko Poron (Partially Found Anime Series; 1974-1975)
Hoshi no Ko Poron (星の子ポロン, Star Child Poron) was a sci-fi comedy anime produced by Nihon Douga that aired from 1974 to 1975 in Japan. 260 episodes were made, at a length of around five minutes each, each having two shorts of at least two minutes long. The titular character, Poron, is an alien child ("star child" as described in the title) who comes to Earth and befriends several animals, almost totally (and naïvely) ignoring humanity.
Eyewitness accounts (on the Nico Video wiki page) state that the anime used a lot of electronic music, and also comment on the short length of the episodes, some of which seem to have been one to two minute-long skits bookended by the opening and ending credits - which in this case, they are.
Unsurprisingly, this show is often confused with the similarly named anime Hoshi no Ko Chobin (星の子 チョビン, Star Child Chobin), which aired only a year after Poron, and Chobin often comes up in searches when looking for information or footage on Poron. Chobin was more successful, having been dubbed into Italian and enjoyed by Japanese audiences of the time.
Going back to the Nico Video wiki, there seem to be a few previews and episodes available, but are possibly region-locked to those outside of Japan or even taken down by Nico Nico Douga in line with Japan's strict copyright infringement laws.
Outside of scant clips on the Internet, there are no listings for Poron on home video on Amazon.jp or any other shopping sites. Out of 260 episodes, the majority remain missing.
UPDATE 31/05/2016: I (Achoo) have found a YouTube channel under the name of "poronist" who is uploading episodes of Poron. The episodes and channel can be found here: https://www.youtube.com/channel/UCKIMXL0Sjp_b1LiDTlIIzaQ As of updating, there are only 10 episodes, a total of 20 two minute segments - with hopefully more to come.