Hermit crab
This is from the book Knitted Amigurumi Sea Creatures by Hansi Singh.
Angler fish
From the same book, but with an adaptation. The parasitic male is intended to be sewn on, but this one is held in place with a magnet. When he is attached, the magnet operates a switch to turn on a bulb in its "lure".
Here is the link to get the book:
Here is the link to get the book: