I have 2,000 family members.
If I lose an arm, I can grow it back.
I pump water instead of blood through my body.
What am I?
Commonly referred to as starfish, these marine animals are not fish at all.
Instead these ocean animals are known as echinoderms, which include animals such as sand dollars, sea cucumbers, sea lilies, sea urchins and of course starfish.
As echinoderms, scientists have been pushing to use the name sea star instead of starfish as the name “starfish” may confuse people about what these marine animals actually are.
For the sake of familiarity, we shall refer to them as starfish.
Physical Characteristics and Appearance
When it comes to starfish they have a number of interesting features that make them so fascinating to people.
For starters starfish do not have a brain, however they are able to feel and make decisions using their senses.
A starfish can interpret its environment, look for food and respond to pain or danger by trying to move away or avoiding it.
In terms of appearance most starfish have five arms that extend from a circular middle.
The five arms stretching out from the center resemble a star, hence the name starfish or sea star.
Depending on the species, some starfish can have more than five arms.
Typically taking on a symmetrical appearance, certain species of starfish can have 7, 10, 15 or more arms with species such as the Antarctic starfish (labidiaster annulatus) possessing as many as 45 arms!
As stated earlier starfish that lose an arm are able to regrow that limb over time.
What’s more interesting however is that among certain starfish species the limb that is cut off or severed from the starfish can grow into a completely new, identical copy of the original starfish.
The surface of each starfish is what identifies its species.
The top of the starfish is called the aboral side while the bottom of the starfish is known as the oral side.
To help with digestion starfish possess two stomachs instead of one.
Instead of blood this marine animal has a hydraulic water vascular system to provide it with sea water and refill its necessary water functions.
This particular system helps the starfish feed and move through the water.
They also have tube feet found on the underside of each arm to help them navigate the ocean and move around.
Instead of having eyeballs, starfish have an eye-spot.
On the end of each arm, their eye-spots can sense light and dark.
Having eyes allows starfish to make decisions based on where they should move in order to find food and safety.
What makes this so interesting is that this allows starfish to make basic decisions and navigate the ocean, even though they have no brain to tell them what to do.
When it comes to color starfish come in many different colors like red, pink, orange, yellow, green, blue, white, brown, purple and black.
As far a speed is concerned starfish are very slow moving ocean animals that are known for their snail like movement speed.
Even the fastest known starfish are only capable of moving a few feet per minute, however it is unlikely that they will sustain this speed for very long.
Slower starfish appear to barely move at all when viewed by the naked eye.
Starfish are amazing ocean animals that are able to make basic decisions without a brain, regrow their limbs when they are cut off and filter water through their body instead of having blood.
Habitat and Migration
When it comes to habitat starfish are mostly found in rocky places and can live all over the world (as long as they are in the ocean, of course)!
In order to survive starfish inhibit saltwater environments (starfish cannot survive in freshwater) and tend to inhibit coral reefs, tidal pools and wet sandy beaches among other salty areas.
Depending on their size, weight and physical characteristics starfish can be seen inhibiting the bottom of the ocean or floating on top of the surface.
Given their slow moving nature starfish aren’t particularly migratory animals, however they may be carried from location to location by the oceans current.
Diet and Hunting Methods
With such a tiny mouth, it is hard to imagine a starfish eating clams but it does!
It grabs its prey with its arms; pulls open the clam or mussel with superhero strength.
Then it pushes its stomach through its mouth to eat its dinner.
After digesting its food, the starfish’s stomach slides back into its body.
They eat all of their food this way including clams, mussels, snails, barnacles and small fish with the majority of their food consisting of clams and oysters.
In rare cases starfish may also consume other forms of prey and marine mammals.
In fact a group of starfish have even been observed consuming the carcass of a deal seal pup.
Living in the ocean can be dangerous for all marine life.
They are always at risk for water pollution.
This is especially true for the starfish because of its water vascular system.
Split oil or polluted water pumps through a starfish’s body and poses as a life-threatening risk.
Aside from pollution, a starfish’s marine predators include fish, seabirds and sea otters.
They protect themselves with armor.
No, not helmets or shields, but a spinney armor on the tops of their bodies.
They are covered with small spines made from pates of calcium carbonate.
This robust covering helps protect them from becoming dinner.
Reproduction and Breeding
Starfish can reproduce both sexually and asexually depending on species and may change its gender when necessary.
Also, dependent on the type of starfish, there can be separate male and female echinoderms.
Just looking at a starfish you could not tell whether it is male or female.
Starfish produce chemical signals to attract each other to mate.
During spawning, you can tell the difference as the male will climb on top of the female, wrap his arms in hers and release his sperm into the water.
The female will be encouraged by this and will then release her eggs.
Starfish can also regenerate arms that have been broken off.
So, what happens to the fragmented piece?
It can regenerate into an entire starfish body—asexual reproduction occurs.
A new organism can start to grow into a brand new starfish.
While regeneration of a new body is an amazing feat it is important to point out that not all species of starfish are capable of generating a whole new body from a severed limb.
With thousands of starfish species in the ocean, their lifespan differs greatly.
Usually larger starfish live longer than the smaller species.
According to National Geographic the average life span for a starfish in the wild is up to 35 years.
For a marine animal that doesn’t have a brain and eats their food from the inside out, starfish are quite fantastic.
Starfish may also be threatened by diseases, bacteria and pollution.
Their slow speed can put them at risk of being washed on shore where they are unable to move quickly enough to get back into the water.
Unless the tide brings them back in they are likely to dry out and die or become food for land dwelling animals such as marine birds and sea otters.