Board Thread:Questions and Answers/@comment-45001894-20200207174929/@comment-27045866-20200207180619

The shell you see in the picture isn't necessarily the shell they were born with as:

"They can solidify their egg white and make it like an egg shell, and should a man put up fierce resistance, they'll use that to bind him more strongly. Depending on the circumstances, they may cover all around themselves and their man with their shell."

They are slimes, since they can replace the parts of themselves that is eaten since their jelly has magical effects, it makes sense they can grow to their normal size fairly quickly after hatching.