Tag Archives: Sea Stars

One Feet, Two Feet, Tube Feet!

How do all of these spiny creatures move around? What’s the secret behind of all those tiny, squishy legs underneath? First, you must know that those little legs aren’t legs at all. If you were to examine the underside of a sea star, also known as the oral side (where the mouth is located), you would see rows and rows of tube feet. Tube feet are used for locomotion for most echinoderms. The phylum that groups together sea stars, sea urchins, sea cucumbers and many others of similar kind is called Echinodermata, translating to “spiny skin.” All echinoderms possess spiny skin, operate on a water vascular system, and can regenerate arms, or even digestive systems in some sea cucumbers.

tube feet sea urchin

Here is a closer look at the tube feet of a Bat star!

tube feet sea star

This is the oral side (underside where the mouth is located) of a Bat star! Here you can see the 5 arms of the creature and the rows of tube feet inside each one.

For most echinoderms, the tube feet are the primary link between the water vascular system and the outside world. Water vascular system means instead of blood, like most animals, these creatures have water running through their body to help with all their movements.

On the top of a sea star, sea urchin or other echinoderm, there is a small round portal called the madreporite. The madreporite brings water inside the body of the animal. Inside the animal, there is a network of canals that send water through the body. If you didn’t know already, echinoderms possess pentaradial symmetry, meaning that there are five identical arms extending from one central disc! On each arm, there can be up to hundreds of tube feet.

tube feet diagram

If looking at the picture of the sea star, you will see the internal canals and how on each arm the canals end at the tube feet. Once a sea star sucks in water through the madreporite (hole on top), the water then travels through all the tunnels to each arm of the creature. Within each arm, the tube feet use the pressure of the water to move over surfaces. Not only do the tube feet provide excellent, fast movements but they are also used for powerful suction when pulling apart shells of prey!

For example, the common starfish will use tube feet to pry apart the shells of oysters and mussels to get the mushy insides. Another example is the feather star, which will raise its arms, wave its tube feet around, and catch plankton to bring towards the mouth on the underside. Unlike sea stars and sea cucumbers, the common sea urchin has a beak that it uses for scraping algae off rocks. Instead of using tube feet as a function for capturing prey, urchins mainly use the tube feet as a means of transportation or quick retreat.

tube feet 1

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Written by: Madison Eggenberger

Mythbusters: Sea Stars have eyes?

Now there have been many questions about where the eyes of a sea star are actually located.

Some say that the eyes are located on the mid section of the sea stars while others say they have no eyes at all. Multiple animated movies and cartoon shows depicts a sea star with eyes on the mid section of their body, so many people actually believe that the eyes are located in that spot.

However, what if I told you that the eyes of the sea star are not located there? What!?! Yeah it’s hard to believe when your favorite child hood cartoon leads you with false details of a sea star’s anatomy.

The eyes of a sea star are actually located at the ends of each on of its arms! So depending on how many arms a sea stars has determines how many eyes they have. These eyes however are not like the eyes you and I have. These eyes cannot see much detail or color, but they can see shadows and lights. This helps them identify if an organism is bigger or smaller than they are so they can decide if it is a predator or possible prey.

Now I bet your wondering, why would cartoons and movies make a sea star out to have eyes on it mid section? Well, can you imagine how scary that cartoon or movie would be for children if they saw the talking sea star with five or more eyes walking around? Yeah, it would probably give those children nightmares of those cartoons and movies for a long time.

Your next question maybe, what is actually located on the center of the sea star? Well that will be another question to answer in the next Mythbusters!


Sea star in hand

How Sea Stars Feed

Sea stars belong to a group of backbone lacking invertebrates called echinodermata, which means “spiny skin”. Sea stars are fascinating animals with a crazy eating strategy! Sea stars begin by climbing on top of the prey using their tubed feet that function using a water vascular system. This means they take in water to their body through an opening called the madreporite and use water pressure to function their feet. If the sea star finds an animal with a hard exterior, such as a mussel, it can use this water pressure and tubed feet to open the prey exposing the soft interior. Some sea stars can apply 12 pounds of pressure when prying open prey!

Once the prey is opened or under the center of the sea star, the sea star excretes its stomach. The excretion of the stomach is referred to as eversion. With the everted stomach inside the prey’s protective covering it then begins to digest the soft tissues with digestive enzymes from the stomach. Even if the prey is a tightly sealed mussel as long as the sea star can find a tiny opening it can get its enzymes inside to devour its prey. Once the enzymes liquefy the meat of the prey it is then absorbed by the stomach tissue. The final digestion of nutrients is done inside the arms of the sea star by the organs called pyloric ceca. Once digestion is complete the stomach is then pulled back into the mouth and any hard parts of the prey are left behind.

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