Starfish: characteristics, reproduction and taxonomy

Starfish ( Class Asteroidea ) are one of the most characteristic invertebrate animals of marine ecosystems. Among the main characteristics of sea stars we can highlight:

• 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.
• Sea stars are animals that do not have a brain . 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 respiration of the starfish 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 madreporito, a hole located in the rear 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 indefinite growth pattern and their amazing capacity for regeneration . When they suffer the dissection or breakage of one of their arms, these 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 as it depletes 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.

The taxonomy of the starfish , that is, its classification based on its 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 also belong. (class echinoids) and the holothurians or sea cucumbers (class holothuroids).

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

The taxonomy of sea stars is:

• Domain: Eukaryota
• Animalia Kingdom
• Superphylum: 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 on the taxonomy of starfish, you will find information on the types later, because after the Class it is the next step in the taxonomic classification.

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

Where do starfish live

The habitat of the starfish is the oceanic waters of the whole world, from the Atlantic to the Pacific, as well as by the Indian and even by 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

As for the food of the starfish , these 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 invertebrates. benthic. They tend to follow a generalized mode of attack on their animal prey, which they will later digest, intraorally or extraorally (using an everted stomach with mucus). At other times they simply choose to feed on different suspended particles.

With life cycles of great complexity, the reproduction of the starfish can be carried out both through sexual reproduction (with exchange of genetic material with another organism of the opposite sex of the same species) and by asexual reproduction (without exchange genetic nor the need for another individual to reproduce).

In the latter case, the curious process of physiparity stands out 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 capable of regenerating the rest of its body (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 Hermaphroditic Animals: reproduction and examples . Below we offer two diagrams of the reproduction of starfish

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 cells of the skin , which allow them to perceive the environment from any angle and differentiate the light and the marine currents.

Did you know that there are up to 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:

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

Taking a starfish out of the water in which we have found it to take a photo with it or even take it 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 when removed from their natural habitat, starfish die from not being in contact with salt water , drying up 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.

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