Starfish belong to the Asteroidea class. It is also called the fragile star. There are 2000 species living in all the oceans of the world: Pacific, Atlantic, Indian, Arctic and South Ocean (Antarctica).
Sea stars are found at various depths, some larger than 6000m. They are most familiar with marine animals and have a number of well-known features such as regeneration and feeding on mussels.
They vary according to individual species and possess a sea have a great variety of shapes and modes of feeding.
The digestive system is quite complicated. I will come back to him when I make a classification of the species of the sea stars. Until then a small summary … The mouth is located on the underside of the body and opens through a short esophagus.
First open the clam. Then he removes his stomach from his mouth and inserts it between the shells. The stomach secretes enzymes with help to digest the victim.
Because of the ability to digest food outside the body the sea star is able to hunt larger prey than its mouth such as shells, oysters, arthropods, small fish and mollusks. The starfish feeds mostly on shells.
Not all species are carnivorous. In the absence of meat, they can supplement the diet with algae. It sounds strange, but some algae actually graze on the bottom of the seas and oceans.
The starfish expresses a pentadridial symmetry at maturity. However, it is believed that the ancestors had bilateral symmetry. The most common star has 5 rays or arms. They are species with 6 or more arms because of developmental anomaly.
Other species simply have more, for example the Solasteridae species can have up to 50 arms. These organisms are composed of calcium carbonate. The bottom surface contains the oral surface and the upper surface is stronger, and it also has a protective role.
From the body surface, several structures can be identified that include the basic anatomy of the animals and can sometimes help to identify it. The 5 arms move on dozens of legs. The tubular legs move when the water is pumped through them inside and out.
A channel system drives the water to the feet. There are some pumps on these channels. They regulate water circulation. The starfish absorbs water through a filter.
At the end of each arm there is a microscopic eye with which the starfish can see where it moves. There are no corneas or iris.
Many types of toxins have been extracted from various large starfish species for research and pharmaceutical or industrial worldwide.
Breathing occurs primarily through small-sized tube tubes called papules. The oxygen in the water is distributed throughout the body.
Excretion also occurs through this tube system and the papillae.
Starfish can reproduce sexually or asexually. Most species are hermaphrodite. One species is born male and later turns into a female.
Sexual dimorphism can not be seen from the outside. The eggs after they have been deposited need only to be covered and flaky. Sea stars gather during propagation, and they do not know how they communicate, but they all multiply on the same day.
If a arm is broken, it is regenerated only if at one end it has a part of the central disk, that is, only the part caught by the body. Life span varies between species, larger species live longer.
A species reaches sexual maturity in 2 years and lives about 10 years, another reaches maturity in 5 years and lives 30-40 years.