Right off the start, the proper scientific name for these animals is “Sea Star” not “Starfish”. They are invertebrates and not a fish nor do they have a backbone. Sea Stars belongs to a large group of marine animals called echinoderms. They can be found in all oceans of the world. Largest populations of Sea Stars live in the Indian & Pacific oceans. Sea Stars are usually located in the shallow water. There are more than 2,000 species of Sea Stars and not a single one can survive in freshwater. Sea Stars belong to the group of marine invertebrates which also include Sea Cucumber, Sea Urchin and Sand Dollar. Their star-like shape is the reason why they are named Sea Stars. Most species have 5 arms, but there are Sea Stars with 10, 20 or even 40 arms. Sea Stars with 40 arms is called “Sun Stars” and vary in size. They usually have 5 to 10 inches in length and weigh up to 11 pounds. Sea Stars are not hermaphrodites (animals which have characteristics of both genders) but they are capable of changing the gender whenever they like during their lifetime. Sea Stars can survive up to 35 years in the wild.
A common feature for all Sea Stars is that their body is radially symmetrical. That means that their body can be divided in five equal pieces (even if they have more than five arms). Another impressive characteristic of the Sea Star is their ability to regenerate different (missing) parts of their body. If predator eats part of the Sea Star (one arm for example), the remaining part of the animal will develop missing arm(s) and bring back previous look after some time. This process is not always fast and it may last up to one year. The Sea Star is a carnivore who likes to eat clams, shells and mussels. It has two stomachs, one of which can be pushed outside the body during eating. This tactic allows them to eat large prey that cannot be swallowed with their small mouth. A Sea Star’s mouth is located on the underside of its body and its anus is located on the upper side of the body. Sea Stars move using tube feet, which consists of hundreds projections on the underside of their bodies. They are used for walking and catching of the prey. Sea Stars do not have a brain. They also do not have blood like other animals. Instead of blood, sea water circulates through their body with the help of sieve plate. The surface of the Sea Star’s body is covered with bony skeleton which often contains different kind of spikes & thorns which serve as excellent protection against predators. Typical predators of the Sea Star are sea otters, rays, sharks, seagulls and different types of fish. Sea Stars can reproduce sexually by combining reproductive cells of males & females or asexually by dividing its body at the center and by regenerating the missing part. During sexual reproduction, males and females release millions of sperm and eggs in the water, where they mix together to form a fertilized egg that develops into new Sea Star. The female is capable of producing millions of eggs at once. This is important because only 4% of the eggs survive to become adult Sea Star.