How do the tube feet of a starfish pull open shells mollusks?

Starfish don't actually "pull open" shells using their tube feet. They use a combination of their tube feet and powerful muscles to pry open the shells. Here's how it works:

1. Adhesion: The starfish uses its hundreds of tiny tube feet to grip the edges of the mollusk's shell. Each tube foot has a suction cup-like structure that allows it to hold on very firmly.

2. Pulling: Once firmly attached, the starfish uses its powerful muscles to pull the shell open. This force is applied slowly and steadily, much like a person trying to open a jar lid.

3. Hydraulics: The tube feet themselves don't provide the strength to pull open the shell. They act like a system of levers that are powered by hydraulic pressure within the starfish's body.

4. Persistence: The starfish can apply this pressure for hours, slowly tiring out the mollusk and making it easier to pry open its shell.

5. Feeding: Once the shell is open, the starfish everts its stomach through its mouth and into the shell. It then digests the mollusk inside the shell before withdrawing its stomach.

Key points:

* Tube feet are not strong enough to pull open shells on their own. They act as anchors and levers.

* The starfish's muscles are responsible for providing the force to open the shell.

* The process is slow and persistent. The starfish can apply pressure for hours if needed.

* The starfish uses its stomach to digest the mollusk inside the shell.