1.An Echinoderm, not a Fish

Starfish do not belong to the fish group; they belong to marine invertebrate group called echinoderm. Starfish are also called sea stars and are related to sand dollars, sea cucumber and sea urchins. They have a star-like shape which is the reason behind their sea star or starfish name.

2.Starfish Species

There are over 2000 species of starfish on all oceans of the world, from cold sea floor to the tropical habitants. However, the largest starfish populations are found in the Pacific and Indian Oceans. Starfish tend to inhabit shallow waters and none of the 2000 plus species survive fresh water. Only a few starfish species inhabit brackish waters. Most starfish species have 5 arms but there are starfish species with 10, 20, even 40 arms. The species with 40 arms is known as sun star.

3.Adaptation Mechanisms

Starfish have calcified, bony skin that offers protection against most predators. They have striking colors that aid in camouflaging or scaring potential attackers off.  Their bodies are covered by bony skeletons that contain various kinds of thorns and spikes. These help protect against predators. The major starfish predators include sea otters, sharks, rays, seagulls and other kinds of fish.

4.Physical Features

Starfish come in varying sizes. They generally measure 5 to 10 inches and can weigh up to eleven pounds. Their mouths are placed on the lower side of their body and their anuses are placed on the upper side. Their bodies are outwardly symmetrical which means it is possible to divide their bodies into 5 equal pieces.

5.Regenerating Ability

Starfish are capable of regenerating different parts of their bodies. For instance, is a predator eats a part of a starfish, the remaining part develops and restores its previous look. In some cases, starfish regenerate their entire bodies. They do this by housing all or most of their crucial organs in their arms. Some starfish need the core part of their body to remain intact in order to regenerate. Some species however develop and entire new starfish from a section of an injured limb. Regeneration is a slow process that takes up to a year.

6.Feeding

Starfish are carnivorous creatures that prefer to feed on shells, clams and mussels. They have two stomachs. One of the stomachs can get out of the body during feeding. This allows these sea stars to consume a large amount of food which they cannot swallow with their tiny mouths. They use their small tube suction-cupped feet, they pry on oysters or slams before their cardiac sac-like stomach comes out of their mouth and exudes within the shell. The stomach envelopes the trapped prey and digests it then returns into the starfish body.

7.Movement

Starfish have tube feet that have numerous projections beneath their bodies. They use these feet to move from one point to another. These tube feet also serve the purpose of trapping prey. Starfish don’t have a brain.

8.Circulatory System

Unlike other animals, starfish have no blood. These pure marine animals have sea water circulating through their bodies instead of blood. The sea water works with the aid of sieve plates and pumps nutrients through the starfish bodies.

9.Reproduction

Starfish reproduce both sexually and asexually. When reproducing sexually, females and males release millions of eggs and sperm in water. They mix to form fertilized eggs that grow into new sea stars. Female starfish have the ability to produce millions of eggs at a go which is necessary because only a small percentage of eggs live to adulthood. Asexually, starfish reproduce by dividing their bodies from the center and regenerating missing parts.

10.Ability to Change Gender

Though starfish are not hermaphroditic animals, they have the ability to change gender in their lifetime when they wish. In the wild, starfish can live up to 35 years.