starfish (Asteroidea) calls actually Asteroidosis with around 1.500 species distributed by oceans around the world. Is a invertebrate animal, with the ability to regenerate. It is well known for its star shape and extremely popular with children.

Starfish on the beach

Starfish on the beach

Features

The starfish normally have a central disk and five arms, although there are species with a higher number of arms such as Labidiaster annulatus that has 50 arms. The central disk is the star's center of activity and also contains the mouth on the lower surface.

They usually measure between 12 - 24 cm in diameter but there are species that measure less than 2 cm and other species can measure up to a meter. Life span varies between species, but is longer in larger species. For example, the Leptasterias hexactis species weighs about 20g and lives for about 10 years and the Pisaster ochraceus species weighs about 800g and has a life span of 34 years.

The top surface of the star may have a smooth, grainy, or spiny texture, and is made up of overlapping plates. The color of the different species varies in various shades of red, orange, blue, gray or brown.

The inner skeleton is made of plates that can articulate with each other. They lack blood, which is replaced by a water vascular system that accesses through an opening in the central part of the body called madreporite. This leads to a central channel with several channels leading to each of the arms. Under this system are also the tube feet that have sensory functions and are located at the end of each radial channel.

Most species can release the arm as a method of defense and regenerate it later. There is also the possibility of regenerating another star, from the lost arm since it contains most of the organs such as the gonads and the pyloric appendix.

Habitat

The starfish inhabits the oceans of the entire planet, but the greatest diversity of species is found near the coast in shallow waters. But like all echinoderms, they maintain a delicate internal electrolyte balance that is in balance with seawater so they can only live in a marine environment and is not found in any freshwater area.

The areas where they can live are tropical coral reefs, rocky shores, tide pools, mud and sand to kelp forests, seagrass beds at a depth of up to 6.000 m.

Food

The starfish is an omnivorous animal, which generally feeds on microalgae, sponges, bivalves, snails and other small animals. Some species of starfish such as the crown of thorns feed on coral polyps, while other species with detritivores, that is, they feed on decomposing organic remains and fecal matter. Other species are capable of absorbing nutrients from the waters around them.

In order to digest complex organisms, it has two stomachs. The first stomach is used to digest its prey, while the second is used to expand it abroad and hunt its prey.

Predators

The starfish, being very slow, has many predators such as fish, crabs, rays, sharks, humans and birds when it is dragged towards the coast.

Reproduction

The starfish, in most species are gonocorean, that is, there are separate male and female members. Their sex cannot be visually identified, only when they spawn.

Certain species are simultaneous hermaphrodites, being able to produce ovules and spermatozoa at the same time since they have both sexes, even in some of them a single gonad can produce ovules and sperm. Other species, such as Asterina gibbosa, are sequential hermaphrodites, that is, they begin life as males and change their sex as they grow. In the Nepanthia belcheri species, the female is capable of splitting in half and her larvae will all be male, so when they grow back to being female.

In the vast majority of species the eggs and sperm are released into the water and the resulting larvae coexist as part of the plankton. In other species, females hatch their eggs by evolving or holding them in specialized structures. Breeding can be done in bags on the aboral surface of the starfish, within the pyloric stomach, or even within the gonads themselves.

Some species the eggs are large and their larvae feed on the yolk, turning directly into miniature starfish without having an intermediate larval stage. Other species feed on other eggs and embryos in the brood pouch.

The female can release more than 2 million eggs, although the average is 1 million. The eggs released by the female are fertilized by the male and once the larvae hatch they are able to swim. The larvae will take about three weeks to settle and begin metamorphosis into an adult starfish.

Asexual reproduction

Certain species are able to reproduce asexually when they are adults by fission of their central discs or by one of their arms. The way to do it depends on the species, but some are capable of regenerating their entire body from a small portion of their arm (1 cm) but the star will suffer a weakness in its structure.

In certain species, when conditions require it, the larvae can reproduce asexually even if they have not reached sexual maturity. They do it through the autotomization of some parts of their bodies or through sprouting. Although this costs you energy and will delay maturity.

Starfish regenerating

Starfish regenerating

State of conservation

The starfish populations are currently losing population and it is classified as a threatened species as it has lost its habitat due to the pollution of its waters.

Relationship with humans

Starfish are very important to humans as they are used in various ways.

Research

Starfish are deuterostomes, closely related, along with all other echinoderms, to chords, and are used in reproductive and developmental studies.

Another area of ​​research focuses on the ability of starfish to regenerate, being simpler than human stem cells that are unable to differentiate from other cells.

Legend and culture

The starfish appears in various cultural works such as the Australian aboriginal fable told by the Welsh school principal William Jenkyn Thomas (1870-1959). In 1900, scholar Edward Tregear documented The Song of Creation where among the "uncreated gods" is a starfish.

The Starfish and the Spider is a 2006 business management book by Ori Brafman and Rod Beckstrom; where it suggests that a decentralized company can flourish (just like starfish do).

In the animated television series SpongeBob SquarePants (Nickelodeon), the namesake character's best friend is a silly starfish, Patrick. Other characters like him Mister crab y Calamardo they are animals.

Patrick the starfish

Patrick the starfish

Collectables

In some cases, starfish are taken from their habitat and sold to tourists as souvenirs, ornaments, curios, or for display in aquariums.

As food

Few species of starfish are edible, the vast majority contain saponins that have an unpleasant taste, others are poisonous and others can transmit paralyzing intoxication.

They are sometimes eaten in China, Japan, and Micronesia. On the island of Huamobel, the way to do it is to cut it, squeeze it and cook it with sour tamarind leaves. The pieces are left to dry for several days and the outer skin is removed and cooked like coconut milk.

Industrial and military history

In the hardware and software industry its name is used as a metaphor in networks, companies and tools. In the military industry, it is the name of several ships of the Royal Navy.

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