Students read "A House for Hermit Crab" by Eric Carle, then made their own hermit crabs!
Students got seashells and a small amount of red Model Magic. They rolled the clay in their hands into a little worm and stuffed the shell with it so the outer parts of the crab had something to stick to. They then got more clay to create a head for their hermit crab, then legs and claws.
When they finished, they were able to decorate their hermit crabs' houses with stickers. I have also tried giving students permanent markers in different colors; it just depends on your population and what they are able to do.
The next class when the hermit crabs were dry, we made them a habitat to live on. I had pre-cut little squares for the habitats. Since crabs like shallow water, we attached a piece of sandpaper to represent sand on the cardboard, then collaged blue cellophane and tissue paper for water.