Green Hour Challenge #1...

The Green Hour Challenge (No Child Left Inside) looks great, and so I decided to use our trip to the beach as a jumping off point. We spent the entire day (well, about 5 hours) exploring a familiar stretch of coast made unfamilar by the very low tide. We saw hermit crabs, a variety of starfish, a few sea slugs, several varieties of seaweed and sea grass, and more!

Elf's two focuses for the week:

Hermit crabs - Why do they live in different types of shells?
Most species of hermit crabs have long soft abdomens which are protected from predators by the adaptation of carrying around an salvaged empty seashell, which the whole crab's body can retract into. Most frequently hermit crabs utilize the shells of sea snails, marine gastropod mollusks. The tip of the hermit crab's abdomen is adapted to clasp strongly onto the columella of the snail shell. As the hermit crab grows in size it has to find a larger shell and abandon the previous one.

Or, as I explained it to Elf, the hermit crabs have unprotected bellies, so they use empty shells of other sea creatures to protect themselves from birds and other animals that might hurt or eat them. As the hermit crab gets bigger, it outgrows the shell just like we outgrow our clothes, so it searches around until it finds a new one that fits better, and then it suctions itself into it.

How do starfish move?
Starfish do not rely on a jointed, movable skeleton for support and locomotion (although they are protected by their skeleton), but instead possess a hydraulic water vascular system that aids in locomotion. The water vascular system has many projections called tube feet on the ventral face of the starfish's arms which function in locomotion and aid with feeding.

My explanation to Elf: Starfish have little tubes, called tube feet, on the underside of their bodies. They can squirt water from these tube feet and move around by essentially jetting themselves everywhere.