Starfish! This marine animal has always generated immense interest owing to its radial symmetry with five or more arms. The starfish or the 'sea star' gets its name from its star-shaped body. It may come as a surprise to many that the starfish is not actually a fish. It is in fact an echinoderm belonging to the class Asteroidea. About 2,000 species of this marine animal are found in every ocean across the world; maximum of these inhabiting the Indian and Pacific oceans. Also, starfish are found in shallow waters, but never in freshwater bodies. In the wild, their lifespan extends up to 35 years. Let us take a look at some more interesting facts about the wonderful sea star.
Did You Know?
Because they are symmetrical by five points, just like sea urchins, they are also called 'Phylum Echinodermata'.
If you have ever encountered a starfish and turned it over, you will find hundreds of projections on its underside. These are known as tube feet, which serve two basic functions - one being able to move around in the water, and the other to open up scallops or clams.
An interesting fact about the starfish is that it has two stomachs. The cardiac stomach can help the starfish engulf food outside its body. When the cardiac stomach comes back into the body, the food in it is transferred to the pyloric stomach.
Have you ever tried locating the mouth of a starfish? It is located on the ventral surface, underneath the upper surface.
The sea star with five arms is the most commonly spotted one. However, there are species that have 10, 20, or even up to 40 arms!
The starfish has an eye spot at the end of each arm; although not much detail can be seen, the eye spot enables the starfish to view movement and differentiate between light and dark.
Most starfish have a spiky or leathery surface, depending upon the species. The crown-of-thorns starfish is known for its thorny spines that are present all over its body. This tough covering on the upper side of the body acts as protection from its predators, as it is made up of calcium carbonate plates with tiny spines.
In addition to no brain, these sea animals do not have a single drop of blood in their body. Instead, they have a water vascular system, and sea water is pumped into the body through a sieve plate. The anus of this invertebrate is located on top of its body.
Amazingly, in case a starfish loses its arm, it is capable of regenerating the same in about a year! This is extremely useful when the sea star feels threatened by a predator, as it can lose the arm and escape. Sometimes, an entirely new starfish can grow from one arm. This phenomenon takes some time and occurs as most of the vital organs are stored in the arms.
These marine animals have a unique way of feeding on their prey. To be able to eat a prey that is larger than its mouth opening, the starfish wraps its arms strongly around the clams or shells, and then jerks it open. Then it pushes the stomach out into the shell and eats up the prey, and finally retracts the stomach back in through the mouth.
An interesting fact about starfish is that they can reproduce sexually and asexually. Eggs and sperms are sent off by the females and males respectively, in the mating season.
These facts about starfish tell us quite a story about the kind of life that exists beneath the sea. Complex, yet beautiful, life beneath the sea has a completely new world in store for us.