Starfish: Characteristics, reproduction, habitat, types and more

In this opportunity you will know everything related to the starfish, one of the most fascinating and beautiful marine species, whose striking color delight anyone.

Main Characteristics of The Starfish

The starfish are invertebrate creatures, which make up a large group of marine species, where cucumbers and sea urchins are probably the most common.

It is also necessary to clarify that the starfish are not fish; they are Echinoderm, which belong to the Asteroidea class.

The starfish are born in the form of larvae, and once they break off from the egg, they start their maritime life, where they remain larvae until they are five years old. At this age they finally become adults, with a life expectancy which ranges between ten and thirty years. Everything will depend on the class they belong to.

There are more than 2000 species of these animals scattered throughout the oceans, which can never remain in fresh water. The starfish are carnivorous creatures whose diet is based on crustaceans and mollusks.starfish: anatomy

The stomach of the starfish has the peculiarity of being able to extract food from the outskirts of the body, since it is completely flexible and can make outward movements to catch its prey and then return to it.

There are wrong beliefs about this marine creature, since people usually think that they are harmful to other marine species.

At first sight the starfish seem to have a simplex anatomy, although the morphologic structure of these creatures is quite complex in each detail.

In this sense we must point out that they exhibit radial symmetry, since their arms are arranged evenly in a circle around a central disc.

Starfish lack of eyes and brain, but they do have one sensory tentacle at the end of each arm.


The starfish usually have 5 arms with ambulacral grooves , although there are also specimens with 20 arms.

Each arm is formed by an internal blister and an external podium or “feet”. In some circumstances, these arms perform displacing functions, since they can work as levers or as a traction system when they are on vertical surfaces.  The speed they can reach employing their arms, ranges between 10 and 14 cm per minute.

The starfish also lack of blood, but they have an aquifer vascular system, which transports salty water through the madreporite  towards their alimentary routes to absorb nutrients.

The aquifer system can be considered as the main element of the displacing function of the sea star.  The ambient water enters the system through the madreporite circulating then from the stony duct to the annular channel and the radial channels.

These channels carry water to the blister (reservoir), which when is compressed, forces the water on the podiums making them expand, so they make contact with the substrate.

The starfish also employ their arms to break oysters and clams to feed themselves. If for some reason they lose an arm, it is quickly recovered, leaving another arm very similar to the lost one.

When the starfish lose an arm in a combat with a predator or in an accident, these extremities once detached become in new stars, since the vast majority of the organs of these animals are located in them.

On the underside of the starfish, they have what are called the tube feet, which possess suction cups. These tube feet allow starfish to cling  to rocks as well as move along the ocean floor.


This is located in the middle of the oral disc; and it is strategically bordered by a peristomial membrane, which is formed by a sphincter. It has a small esophagus, which is directed exactly to the stomach, where there is a division of two parts in common which are the cardiac stomach, and the pyloric stomach.

The cardiac stomach is located in the center of the disk occupying the biggest portion of it.  It contains a large number of folds, and it has the particularity of being able to increase its surface, making the gastric devices leave and giving way to different ligaments and the pyloric caeca, which make up the digestive glands of the starfish.

Color and skin

Starfish have different and very attractive colors, which captivate the attention of anyone..

Their colors range from the brightest to the warmest, and they even use them to hide from enemies or to instill   fear in them.

Orange, yellow, different shades of green, perhaps blue, violet, gray, brown and even many colors at once, can be present in these beautiful creatures.

As far as the skin of this marine species, it is usually very strong, and it has a tissue which contains large amount of calcium.

This feature is quite useful to protect themselves against predators.

Some starfish have a smooth  skin, with small pimples or spines superimposed. What is certain is that the bigger the size, the stronger their skin will be.

Size and weight

Their  size and weight  vary  according to the species, however their measurements generally range between 12 to 25 centimeters in diameter. There are also very small species of two centimeters in diameter, and some other quite big of up to one meter in diameter.

As for their weight,  it also  varies according to the species, and ranges from 20 grams to more than 80 grams. An interesting aspect regarding this trait is that it determines the starfish sexual maturity and even their longevity. The less weight a starfish  has, the less life it will have.

Now, it is time to learn more about them


These marine creatures are the calmest of the aquatic environment, and they usually carry out all their activities at night. During day they tend to be inactive, as a strategy to avoid their predators.

The starfish can avoid an unexpected arrival of a predator, since they have  a system of sensory cells in their skin, that allow them to be attentive to light, marine currents, chemical bonds, among other aspects.

Habitat and Distribution 

The starfish can´t live outside the water, so they are distributed throughout the oceans of the world, either in cold or tropical waters.  It is quite uncommon to find them in freshwater.

The preferred habitats of these striking creatures are the marine depths; they adhere to the muddy, sandy areas, between algae and rocks.

However, the Atlantic Ocean is the preferred habitat of this species during its adulthood, spreading from the coasts of Europe to the limits of the Cape Verde Islands, extending to the entire Mediterranean Sea.

The starfish settle without any problems on the seabed, where they come to live fully uncomplicated. They almost always prefer coral reefs  large agglomerations of algae, and stony places, at depths of even 6000 meters. However, there are also a large number of these creatures located in areas close to the coasts.

Even in their habitats the starfish are no exempt of their most common and fearsome predators, such as fish, crabs, otters and sea gulls.

Although they have a sort of protective system in their bodies, which is based on toxins, spines and grains that produce a rather bitter taste, nothing pleasant to the palate of these animals, they are dragged and devoured by them.

The fact is that they can only be in marine environment, and if they stay out of these waters for a long time they could easily die, since their bodies have a system that helps them have an electrolyte control that only allows them to live in salty waters.

What do starfish Eat?

The starfish are carnivorous, scavenging and even detritivore. Their  diet is based on consuming mostly invertebrates, such as gastropods, barnacles, bivalves, polychaetes, snails, sponges and worms. Given their detritivore condition they can consume vegetables in a state of decomposition and also fecal materials.

The starfish have the ability to move their stomach outwards, in order to reach their prey and spray them with a segregation coming from the enzymes, which destroys the tissues of their victims quickly. This skill allows them to catch their prey and taste them with calmness. The slits of the coral reefs are their preferred locations to search for marine plant particles, and they also have the advantage that Plankton of different marine organisms sticks to their bodies, which makes easy their alimentation.

Digestive System

The digestive system of this marine species is composed of a mouth located in the stomach, which has the particularity to revert from an inner position to an outer one.  As far as the anus it is a kind of intestine of straight and short form, which in some specimen doesn´t even exist. Their ambulacra pieces  allow them to trap their prey with their arms.

As for their  stomach it is divided into two parts; the cardiac zone which facilitates external expulsion, giving way to the process of digestion, and the pyloric one that helps perform extra intestinal function, which lasts approximately 12 hours. The digestion process is carried out with the stomach on the outside of the starfish, where the prey remains for a short period of time.

In general, there is a belief that  starfish introduce a poison into the skin of different marine species such as bivalves and mussels,  causing them serious damages. However, according to several researches there is no such poison and they are completely harmless.

In general terms all species of starfish are able to carry out their feeding process outside of their bodies; catching their prey by employing the suction discs. They employ stomach´s membranes  to move to the mouth the prey already decomposed, by the digestive juices

Now let´s learn in a different way….


The reproduction of the starfish can be sexual by releasing their eggs and sperm directly in the sea, or it can even be asexual. Usually the reproduction of the starfish is external, although some species can also present internal fertilization.

Sexual reproduction

Most starfish are dioic, and they are sexually differentiated in males and females, although there are also simultaneous hermaphrodites which produce ovules and sperm at the same time.

Some other species are sequential hermaphrodites, that is, they are born as males and become females as they get older.

The starfish have two gonads in their arms,which release gametes through openings called gonoducts.

The released larvae become part of the plankton in the sea, although there are also some species that incubate the eggs or attach them to their bodies. In these cases the eggs give rise to a tiny starfish that does not go through the larval phase.

Starfish usually gather in large groups to increase the chances of fecundation and spawn together. The reproductive process commonly takes place in winter time, when their cells are fully mature.

Asexual Reproduction

Some species of starfish carry out asexual reproduction when they reach the adult stage, by means of the fission of their central disk or as a consequence of losing one of their arms.

The fission is the process where the atomic nucleus breaks or divides into two or more fragments of approximately equal size. In some occasion the own body of the starfish initiates this process releasing specialized substances that facilitate it.

Larvae of starfish can also reproduce asexually, either by budding or by partitioning or autotomy of a part of the body. In this way a larva can generate many other organisms that will grow as adults if the conditions are good or they can continue to reproduce.

Most Common Starfish

There is a wide variety of starfish distributed in the different oceans of the world. It is known that there are more than 2000 species, and the most common are listed following.


This order is comprised by more than one hundred species, six families and seventeen genres. The starfish of this order have a small inflexible disk and between 6 and 20 long and thin arms.

They live almost exclusively in deep-water habitats, although some inhabit the shallow waters of Antarctica.

In some species, the ambulacral feet have rounded ends and no suction cups.

2. Forcipulatida.

It is a starfish between 25 and 30 cm in diameter when it is adult,  even larger in some ocassions. It has rounded, with the ends curved upwards when the animal is active..

The starfish of this order have different colors, from pale brown to purple or violet, but the orange and yellow tones are the most typical.

They feed on a variety of invertebrates, such as sea urchins or bivalves. They can live up to 10 years. The Forcipulatida inhabit the coasts of the Eastern Atlantic in the northern hemisphere (from the coasts of Norway to Senegal) avoiding the Mediterranean. Live on rocks and stony ground or on substrates where bivalves abound, more rarely on softer substrates, from sea level to about 300 meters deep.

3.-  Notomyotide.

This order has more than seventy species, made up of  twelve genera and only one family. Their  anatomy  is characterized by its flexible arms with bands of longitudinal muscles along its dorsolateral surface.

The central disc is usually small.

4.- Velatida

This order contains about 200 species in five families.

These starfish are characterized by having thick bodies with large discs, and between 5 and 15 arms. The weak skeleton of these starfish confers them a good flexibility.


5.- Valvatida

This order is comprised of almost 700 species, 170 genre y 14 families. The species of this order have a variety of sizes. In the case of the genus Asteria, it is composed of tiny starfish of a few millimeters in diameter.

On the other hand we find the genus Thromidia, whose species reach up to 75 cm in diameter.Almost all species in this order have five arms and two rows of tube feet. See article Blue Starfish for further information about this species

6. Spinuloside.

They are composed of one hundred and twenty five species, made up of ten genera and one single family.


7.- Paxillosida.

This order is comprised by three hundred species with almost forty-seven genera and a small family of only five members.


Main Threats of Starfish

These beautiful marine creatures face constant threats, since they are chased by a large number of predators, including sea lions, newts, crabs, seagulls and in many cases others starfish. Their survival within their own habitat is a true odyssey for this defenseless marine animal.

The several diseases that are caused by different bacteria, as well as the high temperatures of the sea´s water, as a consequence of the global warming, affect in different ways this species. Temperatures of more than thirty degrees centigrade are lethal for starfish.

The pollution caused by human beings also affects the starfish. The different contaminants in the water get inside the bodies of the starfish through their vascular system, and since they lack of a proper filtering system, oils and other pollutants remain inside their bodies in negative way.

The capture of starfish by human beings, does not represent a big threat for this species, which is not considered in danger of extinction

This marine animal, known as a sea star, fulfills an extraordinary regeneration that has been one of its most significant properties. Even when it is thought that they can be harmful to other species, the rumor has been proven false. They only use one type of toxin to defend themselves against predators; it is the only possible defense system in starfish.

There are countries such as China where they consume this type of animal, and where it is considered a succulent dish as well as being coveted.

There is a certain myth about the poisonous sea star. Indeed, it is one of the species that can emit toxins to defend itself from its predators.

Another of their threats comes for their use in aquariums, where they are employed to create, in addition to beauty, an enormous ornamental value. In fact they have also been sold in various industrial establishments of ornamental type.

The Starfish and Human Beings

The starfish are another marine species with important properties  for human beings.  Several investigations have shown that they contain a non-stick material, which can be used as an anti-inflammatory, in very particular cases such as arthritis

This non-stick material found in the drool located on their  body  has interesting properties which allow eliminate viruses and bacteria in different scenarios of chronic and viral diseases.

As a result of all these properties, starfish have been the subject of numerous studies, attracting in an impressive way the attention of large pharmaceutical industries, ornamental and natural medicines.

It is estimated that this slime, as it protects the starfish of any type of bacteria, will do it in the same way with the human being. It also serves to counteract situations in cases of inflammation caused by problems of infections in the body.

The use of these products, based on the slime of this animal has lowered the consumption of certain medicines containing of drugs that harm the body of sick people in some way.

Even though parameters for the administration of this potential natural medicine have not been established, it has been be proved that it will be an effective treatment to counteract diseases caused by bacteria, inflammatory type viruses, various types of fever and even asthma.

Thanks for reading our article about starfish; we invite you to follow us…. By the way…. never too late to watch interesting videos


Deja un comentario