Starfish are echinoderms, along with sea urchins and sea cucumbers. This name comes from Greek, meaning ‘spiky skin’. Their spiky skin is made up of many tiny skeletal plates and spines made of calcium carbonate minerals such as calcite and aragonite. However, because it is an invertebrate it also does not simply have one large protective coat.
What are starfish made from?
Inside, starfish are made of much the same material as you and I, having cells, tissues and organs. However, their arrangement is extremely different and contains a large number of specialisations. The most important difference is that they have a ‘hydrostatic’ skeleton. This means that the body movement and rigidity is controlled using water pressure and not bones.
The body consists of (usually) five arms radiating from a central disc. The mouth is found in the centre of the underside of the body, with grooves running along the middle of each arm containing tube feet. The feet often have suckers on the ends to allow the starfish to grip the ground.
What do starfish eat?
Starfish eat mussels and clams as well as barnacles, snails, and fish. Starfish are typically predatory and interestingly, when feeding they push their stomach outside their body and digest their prey where they are found, then draw their stomach back inside.