Echinoderms are a phylum of animals that are made up of an important diversity of exclusively marine fauna. On our site, we want to present you this time to a specific group of this phylum, which is represented by the class Asteroidea, which we commonly know as starfish, which is made up of about two thousand species distributed in all the world's oceans. Eventually, another class of echinoderms, called brittle stars, are designated as starfish, however, this designation is not correct, since although they may have a similar appearance, they are taxonomically different.
Starfish are not the most primitive group of echinoderms, but they have all the general characteristics of these. They can inhabit the beaches, be on rocks, groups of corals or sandy bottoms. We invite you to continue reading to learn more about the types of starfish that exist.
Starfish of the order Brisingida
The order of the brisingidae corresponds to starfish that inhabit exclusively the seabed, generally in a range between 1,800 -2,400 meters, being distributed especially in the Pacific Ocean, in the waters of the Caribbean and New Zealand, although some species are also located in other regions. They can present from 6 to 20 long arms, which they use to feed by filtration and which are provided with long spines in the form of needles. On the other hand, they have a flexible disk on which the mouth is located. It is common to observe species of this order on sea cliffs or areas where there are constant water currents, since this facilitates feeding.
The order Brisingida is made up of two families, Brisingidae and Freyellidae, with a total of 16 genera andmore than 100 species . Some of these are:
- Brisinga endecacnemos
- Novodina americana
- Freyella elegans
- Hymenodiscus coronata
- Colpaster edwardsi
Starfish of the order Forcipulatida
The main characteristic of this order is the presence on the animal's body of some pincer-shaped structures that can open and close, called pedicellariae, which are generally quite conspicuous in this group and consist of a short stem containing three skeletal parts. For its part, the tube feet, which are the soft extensions arranged in the lower part of the body, have flat-tipped suckers. The arms are usually quite robust and have 5 or more rays. They are widely distributed on a global scale, both in tropical and cold waters.
There is divergence regarding its classification, however, one of the accepted ones considers the existence of 7 families, more than 60 genera and about 300 speciesWithin this order we find the common starfish (Asterias rubens), one of the most representative, but we can also place the following species:
- Coscinasterias tenuispina
- Labidiaster annulatus
- Ampheraster alaminos
- Allostichaster capensis
- Bythiolophus acanthinus
Do you know what starfish eat? We explain it to you in this other article on What do starfish eat?
Starfish of the order Paxillosida
Individuals in this group have tube-shaped tube feet, with rudimentary suckers if present, and are characterized by small granule-like structures on the plates that cover the upper skeletal surface of the body. They have 5 or more arms with which they help each other to dig in the sandy bottoms where they can be located. Depending on the species, they can be found at various depths or some may even inhabit quite shallow levels.
It is established that the order is divided into 8 families, 46 genera and more than 250 species. Some of these are:
- Astropecten acanthifer
- Ctenodiscus australis
- Luidia bellonae
- Gephyreaster Fisher
- Abyssaster planus
Starfish of the order Notomyotida
The tube feet of this type of starfish are formed by series of four and have suckers at their ends, although some species lack them. The body has considerably thin and sharp spines, with arms formed by quite flexible muscular bands. The disc is relatively small, with the presence of five rays and the pedicelaria can have various forms, such as valved or spiny. Species in this group inhabit deep waters
The order Notomyotida is made up of a single family, which is Benthopectinidae, 12 genera and about 75 species, among which we can to mention:
- Acontiaster bandanus
- Benthopecten acanthonotus
- Cheiraster echinulatus
- Myonotus intermedius
- Pectinaster agassizi
If you also want to know how starfish reproduce, you can read this other article on How do starfish reproduce?
Starfish of the order Spinulosida
The members of this group have relatively delicate bodies and as a distinctive feature they lack pedicelaria The aboral area (opposite the mouth) is It is covered with numerous spines, which vary from one species to another, both in size, shape, and arrangement. The disc of these animals is usually small, with the presence of five cylindrical rays and the tube feet have suckers. The habitat varies, being able to be present in intertidal zones or deep waters, both in polar, temperate, and tropical regions.
The classification of the group is controversial, however, the world register of marine species recognizes a single family, Echinasteridae, with 8 genera and more than 100 species, for example:
- Bloody Henricia
- Echinaster colemani
- Metrodira subulata
- Violaceous Odontohenricia
- Rhopiella hirsuta
Starfish of the order Valvatida
Almost all the species of starfish in this group have five tubular-shaped arms, in which are located two rows of tube feet and conspicuous ossicles, which are calcareous structures embedded in the dermis that provide rigidity and protection to the animal. They also present in the body pedicellaria and paxilas. The latter are umbrella-shaped structures that have a protective function, in order to prevent the areas through which the animal feeds and breathes from becoming clogged with sand. This order is quite diverse and individuals can be found ranging from a few millimeters to more than 75 cm.
The order Valvatida has been highly controversial regarding its taxonomy. One of the classifications recognizes 14 families and more than 600 species. Some examples are:
- Pentaster obtusatus
- Protoreaster nodosus
- Devil clarki
- Heterozonias alternatus
- Linckia guildingi
To learn more about starfish, we encourage you to read this other article on How are starfish born?
Starfish of the order Velatida
Velatidae have usually robust bodies, with large disks. Depending on the species they have between 5 and 15 arms and many of these have a poorly developed skeleton. There are individuals with small diameters between 0.5 and 2 cm, and others up to 30 cm. In terms of size, the range varies between 5 and 15 cm from one arm to another. Tube feet occur in even series and usually have a well-developed sucker. As for the pedicelaria, they are usually absent, but if they do have them, they consist of groups of spines. The species that make up the order inhabit great depths
5 families, 25 genera and around 200 species are recognized, among which are:
- Belyaevostella hispida
- Caymanostella phorcynis
- Korethraster hispidus
- Asthenactis australis
- Euretaster attenuatus
Other examples of starfish
In addition to the types of starfish described throughout the article, many more stand out, such as the following:
- Captain's Star (Asterina gibbosa)
- Sand Star (Astropecten irregularis)
- Red starfish (Echinaster sepositus)
- Honduras Star (Luidia ciliaris)
- Common Thorny Star (Marthasterias glacialis)
Starfish have an important ecological role within marine ecosystems, so they are of great relevance within them, however, they are highly susceptible to chemical agents, since they are unable to filter easily toxins that are increasingly entering the oceans.
There are several species that are usually found in coastal areas that have tourist use, and it is common to see how visitors to the area they take out the starfish to observe them and take pictures of them, however, it is a very harmful act for the animal, since it requires being submerged to be able to breathe, as we explain in How do starfish breathe? after being out of the water they die. In this sense, we should never take these striking animals out of their habitat, we can admire them but always keeping them in the water