The sea pig, Scotoplanes globosa — a deep-sea sea cucumber
Images 1 and 2: Via Wikipedia. Link 1; link 2. Lindberg, 1882, Report on the scientific results of the voyage of H.M.S. Challenger during the years 1873-76 : under the command of Captain George S. Nares, R.N., F.R.S. and Captain Frank Turle Thomson, R.N. (public domain)
image 3: (the shiny pink one — source)
Image 4: (the sinister-looking one — source)
Image 5: (the other pink one — source)
Image 6: (the toy — source)
Apparently it’s even been made into a toy by Agatsuma! Available on ebay.