I usually refer to this as the kewpee doll-type nudity.
Being reminded of the one Cow & Chicken episode "P.E." where Chicken, Flem and Earl transfer to a different school and get their clothes stolen while in the shower and are forced to find a place to hide while avoiding the other studios (including a few peaks at their kewpee-doll torsos).
Better than to go through the usual taboo motions perhaps.
Sometimes this sort of things shows up now and the. An early use of it was with some baby character in a Woody Woodpecker cartoon "Kiddy League" from 1959. More recently it's been done to death on Family Guy.
In many anime programs, it can vary. Dragon Ball in it's heyday often showed Son Goku in the buff without concern since the character didn't know any better. Many more adult-oriented shows can often get away with far more, but often limit themselves in places such as drawing parts of the human anatomy black or invisible since it's all class if you don't draw the naughty thing happening. Then of course you get the hentai stuff that is anything goes in terms of creative output.
Reminds me of one Aardman-produced short film "Adam", and the way the character simply had it there anyway and that was it, yet they released this on VHS back in the 90's and gave some parents a scare over here!
This can end up getting into a touchy subject as well, and there's been many cartoons were your characters are often half-naked below the waist (Tale Spin brings this to mind).
Those moments always seem unusual if you had to think too hard about it. I'm reminded of Norb and Dag in The Angry Beavers often wearing PJ's to bed and such. It could be a question over identifying certain situations with how we view it in reality if anything.
You can't fault that. Especially with animals since it's a given they're born to the world as they are. It's more through how we anthropomorphize them when you begin to see the human nature come out such as in wearing clothes. Even in drawing animals normally in animation, such concerns over sexual characteristics are handled in rudimentary terms of stereotypes (males=broad-shouldered and stocky, female=sleek and slender), and less on anatomical definitions (since they aren't drawn at all).
Again, it gets to a touch area here. I would say yes if you count moments where an animal's fur is pulled or shaved off leaving it's skin behind (often times this is accentuated with underwear like you wonder how that get under there in the first place).
It was, a classic mainstay from the 1970's version. There's a few anime in the 70's and 80's that often gave you such unusual 'wardrobe malfunctioning' moments such as that, though for transformation scenes, nothing best "Cutie Honey".