There are around 1,900 species of starfish around the world living in the seabed. These creatures can withstand frigid and tropical environments. They are marine invertebrates, meaning they are part of a group of marine animals that lack a vertebral column. The fossil record of starfish dates back to around 450 million years ago, but there are few examples to cite. Scientists describe the trouble of finding intact and older starfish remains due to their disintegration after death. Usually, only parts of the animal are preserved, such as the ossicles. 

A few species of starfish, such as the reef sea star, have become known as “keystone” species. This means that scientists monitor the species with a particular emphasis. If the species is declining, they know that something has gone wrong in the broader environment and that other marine species are likely suffering. 


Appearance 

Starfish can be found covered in a smooth surface or covered in spines or bumps. There are also examples of species covered in overlapping plates. The color varies from bright shapes of orange and red to more muted colors, like blue and grey. 

Starfish make use of tube feet that are controlled by a hydraulic system. This means that their feet, technically known as podia, are small tubular projections that occur on the underside of the arms of the starfish. Other creatures, like sea urchins and sand dollars, also have tube feet. 

Pale-colored starfish
Pale-colored starfish

Their mouths are located at the center of the oral or lower surface, something that benefits their feeding habits (described below). 

Amazingly, starfish are capable of growing back limbs that are removed or damaged. They can even remove their own limbs as a means of self-defense. For example, if a predator took hold of one of the starfish’s arms. It might break that arm off and be given time to evade being eaten entirely. 

Diet 

Starfish are opportunistic feeders. This means that they do not actively hunt for prey. Instead, as they move through their lives, they eat what they come upon. 

A few species have specialized behaviors that allow them to participate in suspension feeding. This means they can eat particles suspended in water. This includes zooplankton, bacteria, and other detritus.  Some species are detrivores. This means that they feed on decomposing organic matter, such as fecal matter. Other species have specialized tube feet that allow it to dig itself into the substrate to pull prey, like clams, out. They use their adductor muscle to pull the prey apart and then insert their stomach into the shell, as noted in Zoology. 

Interestingly, there have even been reports of cannibalism among young starfish, according to  “Researcher reports cannibalistic echinoderm underwater dwellers.” 

Habitat 

Starfish can be found worldwide. They live in the frigid polar regions as well as in the warm tropical regions of the world’s oceans. But, the widest variety of starfish resides in coastal areas. It is impossible for starfish to live in freshwater habitats. This is due to a delicate internal balance they need to maintain with their electrolytes. Common places to find starfish are in tide pools, coral reefs, mud, sand, and kelp forests. They have been discovered as deep as 20,000 feet below the surface of the ocean.

There have been occasions where scientists have noted that starfish have a negative impact on ecosystems. For example, the destruction of reefs in Northeast Australia by the crown-of-thorns starfish, as described in PLOS ONE. 

starfish on the beach


Reproduction 

Starfish can reproduce sexually and asexually. This means that they can produce young with and without a partner. Most species have distinct male and female members but not all of them. Some are simultaneous hermaphrodites. This means that they are capable of producing eggs and sperm at the same time while other species change from male to female as they age. 

Threats 

Starfish face numerous threats within their own habitats. They are preyed upon by sea birds, crabs, sea anemones, and other starfish species. Some have defense mechanisms, such as toxins, to repel predators, while others depend on camouflage or spines on their appendages. 

Some species suffer from a wasting disease that is caused by bacteria. This has caused widespread deaths. 

Starfish, like many other species, are also sensitive to changing ocean temperatures and pollution. Ocean acidification is also a cause for concern. 

Underside of a starfish
Underside of a starfish


Facts about Starfish 

  • Starfish can be found covered in a smooth surface or covered in spines or bumps.
  • Starfish can reproduce sexually and asexually.
  • Starfish can be found worldwide.
  • They are capable of growing back limbs that are removed or damaged.
  • A few species of starfish, such as the reef sea star, have become known as “keystone” species.
  • The fossil record of starfish dates back to around 450 million years ago.


FAQs 

Can starfish hurt you?

No, starfish are not poisonous. They can’t hurt you if they pick you up. But, it’s important not to touch the spikes. These can contain a venomous substance that could be dangerous if it penetrates one’s skin. 

What is special about starfish?

Starfish are beautiful and diverse animals. They live in a wide variety of ecosystems, from warm and tropical to frigid. 

Can starfish be eaten?

Some people do eat starfish. But, only a tiny portion of the animal is edible– the meat inside each leg. 

Are starfish friendly?

Starfish spend most of their lives alone but sometimes can be found in large groups in feeding areas. They have no interest in spending time with human beings.