This is Twittle, a plush made by Russ Berrie. I'd place it sometime between 1979-1981 as the production year as I had one as a baby. They might've been made even later than that, I don't know how long they were made. It has a wind-up key on the side that plays "It's A Small World" on an 18-note music box with a metal rod that moves the head in a circle.
This... I found this on eBay searching for Twittles. It's made by Eden, no date on the tag but we'll assume around the same time period. Similar appearance and color, same mechanism. I bought this as well as a curiosity purchase, it plays a music box 18-note tune of Victor Young's theme to "Around The World In 80 Days"
This was also on eBay, the seller tags it as another Eden product(I'm going by seller description). This one is beaten up some but same concept- yellow turtle with a pink and blue shell, wind-up mechanism, blue eyes.
And then today, I spot this one, made by Bantam. Again, same idea, but new company.
They all have the same basic design- yellow body, shell that divides between pink and blue, blue eyes with black pupils, pink nose and mouth, and a wind-up music box inside that moves the head. May or may not have lace.
So I thought Twittle was just a very old Russ Berrie plush and was probably lucky to even find them on eBay. But finding similar turtles seems... was this based on something? Was the yellow turtle with a pink/blue shell that played music a popular item in the late 70s? Finding one similar clone is one thing, finding 3 clones is another.
I purchased the Bantam turtle this past week. It doesn't have a mechanism to move the head like the others with the music box towards the back. There are 2 of the smaller Eden turtle son eBay right now but both are overpriced for their condition- one is rather dirty, the other has that torn pink thread in the face and a bad music box. The bigger Eden is also on eBay still, from sellers who want far too much. One sold this past week for about $10, but the ones asking $50 and $80 won't ever get that. These turtles might be rare but there's not much demand. I haven't seen a Twittle listed in months, not since I bought my last one.
Actually, one of the larger lace-bottom Eden turtles sold for $56 recently but it had about half the cardboard tag attached. Maybe collectors only want ones with the tags?
I've still found zero info on who designed them or why there were so many. Russ Berrie no longer exists and Eden is also gone. Both companies were bought out and absorbed into other companies and I doubt they'd be of any help in identifying or providing more info now. Bantam apparently vanished long ago. One oddity is that two of my Twittles are sewn with yellow thread while the other two are sewn with a clear plastic thread that resembles thin fishing line. Aside from the fact I have no idea why this design of turtle was done by so many companies, I don't know how long they were produced, beyond the period of late 70s to early 80s. I can't find any plush turtles more recent that have this base design and color pattern to them.
The Eden and Bantam turtles were made in Haiti, while Twittle was made in Korea.