The growth is slow, so we really don't notice such things in our aquaria, especially with small species we keep in our reefs. It more noticeable with the large species. I've seen it quite often in wild. Seems they sometimes get "attached" to a favorite shell and don't won't to move out till long past the time they should have, pretty darn funny looking too
Kind of like the one that decided a bottle made a good home
BTW, a few months ago I picked up a bottle covered with jingle shells (a species of bivalve), and two different limpet species. I used it for a touch tank specimen and it got more interest than anything else from both kids and adults. Just to the amazement of what nature adapted too
