SEA STAR: Characteristics, Reproduction and Taxonomy

How much do you know about starfish? These amazing invertebrates hide numerous characteristics and habits that make them one of the most interesting and curious groups of marine organisms. With more than 1,500 species distributed by oceans around the world, starfish inhabit different marine substrates throughout the planet, from ocean floors, both sandy and rocky, to colorful and biodiverse coral reefs. In addition, thanks to having few predators, starfish are abundant and easily proliferate in the habitat in which they are found.

Continue reading this interesting article by Ecologist Verde in which you will find all the complete and detailed information about the starfish: characteristics, reproduction and taxonomy.

What is a starfish and its characteristics

Starfish (Asteroidea class) are one of the most characteristic invertebrate animals of marine ecosystems. Between the main characteristics of sea stars we can stand out:

The symmetry of starfish is pentarradial, presenting a pentagon-shaped disk in the center and, generally, five arms of different lengths depending on the species. Also, there are species that have many more arms.
The sea stars are animals that don't have brains. Discover more Animals are brain in this other post.
There are starfish of different colors, both yellow, orange and red, as well as blue, brown and gray.
The surface or skin of starfish is calcified and very resistant, smooth or rough, sometimes presenting some granules or even spines and is characterized by being covered with numerous overlapping plates.
The starfish breath It is carried out by means of a simple osmosis that hardly supposes an energy expenditure to the animal, so that both the oxygen and the carbon dioxide dissolved in the water enter the organism (through the madreporite, a hole located on the back face that allows the entry of water). Subsequently, the gas exchange is carried out thanks to the help of various structures with respiratory function, such as the dermal gills of the papules and the tubular feet.
Another of the most representative characteristics of starfish is their peculiar pattern of indefinite growth and his amazing regeneration capacity. When one of their arms is dissected or broken, they are quickly replaced and regenerated by other arms generated by the central disc of their anatomy. However, if a broken arm has been isolated from the rest of the body, it is able to heal its wound and remain alive for several weeks, although it will eventually die from depleting its own energy reserves. There is a curious case that is the exception to this phenomenon, they are the starfish of the genus Linckia, whose broken and isolated arms are capable of regenerating their own central disk and the four remaining arms.

Starfish taxonomy

The starfish taxonomy, that is, their classification based on their evolutionary biological history, locates them within the class of asteroids, belonging in turn to the extensive edge of the echinoderms to which the famous sea urchins (class echinoids) and holothurians also belong. or sea cucumbers (holothuroid class).

It is important to differentiate asteroids of the class of the ophiuroids, as starfish are sometimes called species of the starfish, while these have certain characteristics that give them a different taxonomic group and adopt the common name of serpent stars in many corners of the planet.

The taxonomy of sea stars is:

Domain: Eukaryota
Animalia Kingdom
Superfilo: Deuterostomy
Phylum: Echinodermata
Subphylum: Eleutherozoa
Class: Asteroidea

Let's see in the next sections more characteristics and types of starfish that exist to learn to differentiate them and get to know them in more detail. So if you want to expand the information about the taxonomy of starfish, you will find information about the types later, because after the Class it is the next step in the taxonomic classification.

Where does the starfish live and what does it eat?

In this section we expand the notions about the characteristics of these marine animals:

Where do starfish live?

The starfish habitat Are the ocean waters from all over the world, from the Atlantic to the Pacific, as well as the Indian Ocean and even the Arctic and Antarctic Oceans.

In addition, it is easy to find them at different depths, so their abundance and representation within ocean ecosystems is quite wide. Sometimes, they are found in intertidal zones near the coasts, while other species of starfish live at great depths and even in abyssal zones, exceeding 6,000 meters deep.

What do starfish eat

Refering to starfish feedingThese are characterized by being opportunistic animals, that is, they adapt to the food they can obtain regardless of whether it is animals, plants or other organisms, although their favorite prey are benthic invertebrates. They usually follow a generalized mode of attack on their animal prey, which they will later digest, intraorally or extraorally (through the use of a everted stomach with mucus). At other times they simply choose to feed on different suspended particles.

How the starfish reproduces

With life cycles of great complexity, the reproduction of the starfish can be carried out both through the sexual reproduction (with exchange of genetic material with another organism of the opposite sex of the same species) as per asexual reproduction (without genetic exchange or the need for another individual to reproduce).

In the latter case, the curious process of fisiparity by which some species of starfish (such as the Mediterranean species Coscinasteria tenuispina) can divide their body into two halves (from a spontaneous fission), each of which will be able to regenerate the rest of their organism (central disc and arms) by itself. Likewise, as we have mentioned before, the genus Linckia can also shed its arms and these by themselves can regenerate their own central disk as well as the four remaining arms. This can also be done by arms that have been broken or cut from an accident or seizure.

Thus, although there are two differentiated sexes, some starfish are hermaphrodites. Here you can discover useful information about Hermaphrodite Animals: reproduction and examples. Here are two starfish reproduction schemes.

Image: El Mar A Fons, ICM yCSIC and Bio444embriologiaunachi

How Starfish Move

The locomotion and adhesion to different substrates that starfish are capable of making is possible thanks to their numerous tube feet and suction cups.

Although starfish are characterized by not moving at high speeds, they do achieve adequate locomotion to escape from certain dangers or to move in search of food or during the reproductive season, generally choosing the night for their movements, for which they are considered nocturnal animals.

For their movements, the sea stars make use of their useful and surprising sensory skin cells, which allow them to perceive the environment from any angle and differentiate light and marine currents.

Types of starfish

Did you know that there are even 7 types of starfish? In this section we will describe the main characteristics of each of them, as well as the name given to the taxonomic order to which they belong:

Order Brisingida (111 species): have 6 to 16 arms in their anatomy.
Order Forcipulatida (269 species): they have numerous small pedicellars in the shape of a claw on their skin, used to defend themselves or even to help them capture their prey.
Order Notomyotida (75 species): the arms of these species are very flexible and muscular.
Order Paxillosida (372 species): they inhabit the sandy and soft bottoms of the oceans and lack suckers.
Order Spinulosida (121 species): they are characterized by the presence of numerous spines on their upper surface.
Valvatida Order (695 species): the best known starfish belong to this order, those with a voluminous body and 5 arms.
Order Velatida (138 species): they are characterized by a large disc that gives them a very robust consistency.

What happens if you take a starfish out of the water

Take a starfish out of the water in which we have found it for take a picture with her or even taking it with us as a souvenir is, without a doubt, one of the biggest mistakes we can make when dealing with the conservation of marine biodiversity. We must understand that being extracted from its natural habitat, starfish die from not being in contact with salt water, drying out and rotting after a few minutes.

Unfortunately, on numerous occasions, people overlook the survival of these wonderful marine animals and do not take into account the value and importance that starfish maintain within the correct balance and functioning of the ecosystem to which they belong.

Finally, we leave here more starfish images precious and of different species, to be able to appreciate the variety that there is.

If you want to read more articles similar to Starfish: characteristics, reproduction and taxonomy, we recommend that you enter our Wild Animals category.

Bibliography

Calva, L. G. (2002) Eating habits of some echinoderms. Part 1: Starfish and snake stars. Metropolitan Autonomus University, pp: 59-65.
Mutschke, E. & Mah, C. (2009) Asteroidea- Starfish. University of Magallanes, pp: 803-829.
Munar, J. (1984) Anomalies in the symmetry of the Asteoidea (Echinodermata). Cases observed in the waters of Mallorca. Balearic Natural History Society Magazine, Volume 28, pp: 59-66.