Starfish, common name for 5 orders and thousands of living species of marine invertebrates characterized by having radially arranged arms provided with tubular or ambulacral feet. Some sea stars measuring only 1 to 2 cm from end to end as adults, but some reach 65 cm. The group is abundant in the oceans at all depths.
have been reported around 7000 living species and about 13,000 extinct species known from the fossil record.
belong to the group of marine echinoderms are found in all seas and oceans.
biogeographic regions:
Ocean Arctic, Indian Ocean, Atlantic Ocean, Pacific Ocean, Mediterranean Sea. Habitat
the exception of a few species that live in brackish water, all echinoderms are benthic organisms found in marine environments. Living in areas ranging from shallow waters in the power lines to the deep sea.
Description
are usually pentamerous, ie, five arms, but there are also species that only have three arms, while others have many more. The body of the starfish consists of a ventral disk and arms. In the face
lower or ventral disc is the mouth, while the top or back is the anus, the presence of which varies depending on the species.
The center of the disc is occupied by the stomach. The esophagus is surrounded by a ring or annular channel, which leave many longitudinal channels (root canals) and arms have the animal, and extending along the same and close to the ventral side.
On the dorsal side, around a year and some distance from him, there madrepórica or madreporic called plaque, similar to a sieve, through which holes penetrate the water outside. This water is transported through the channels hidróforos, passing into the annular channel and from there to root canals that extend along the arms of the star.
These root canals distribute water circulating in a large number of tiny tubes, each of which terminates in a ambulacral feet. These tube feet are kind of hollow tentacles straighten out and move to inject water into vesicles some of which are provided, following the will of the animal. Behavior
Starfish have developed senses of touch, smell and taste, and also respond to light. Feed on a wide variety of products such as deposits on the ocean floor. Small animals can be eaten whole, in the case larger prey, removed the stomach and digest them outside the body. Some starfish eat bivalves covered opening their arms and inserted inside the stomach. Playing
Most starfish have separate sexes and release sperm and eggs into the water, where fertilization occurs and the early stages of development. Sometimes, the mother retains the eggs in the background and protects. Many sea stars have the power to regenerate body parts, and in some species it becomes a common means of asexual reproduction in which each fragment of the parent star new individuals arise.
Classification
are classified into the following orders: Order
Brisinger
Asteroidea deep. They are between 6 and 16 long, narrow arms that are used for food suspensivore. It includes about 100 species in 17 genera and 6 families.
Order Forcipulatida
pedicellariae is characterized by system includes that are usually clearly visible on the surface of the body. Contains approximately 300 species in 68 genera and 6 families.
Order Notomyotida
Asteroidea deep. It has flexible arms with bands of muscle longitudinal along the inner dorsolateral surface. It includes about 75 species in 12 genera and 1 family.
Order Paxillosida
asteroids are capable of digging in sandy sediments. Are characterized by tube feet, tube and pointy, which have been interpreted as primitive by some authors [1]. It contains about 255 species in 46 genera and 5 families.
Order spinulosa
lack of pedicellariae. Fossil forms are unknown. It includes about 120 species in 9 genera and 1 family.
Order Valvata
is a very diverse group who often apparent marginal ossicles. The inclusion of more families in this order is at issue. It includes about 695 species in 165 genera and 14 families.
Order Velata
have robust body with a great record and interradial depressions. Some 200 known species in 25 genera and 5 families.
