Starfish (Asteroidea) are one of the most mysterious animals. Along with sea urchins, brittle stars and sea cucumbers, they form the group of echinoderms, a group of invertebrates that hide at the bottom of the ocean. It is common to see them on rocky shores, while they move very slowly. Perhaps that is why it is so hard for us to imagine how starfish reproduce
Due to their way of life, these animals multiply in a very peculiar and interesting way. They have sexual reproduction, like us, although they also proliferate asexually, that is, they make copies of themselves. Do you want to know how? Do not miss this article on our site about the reproduction of starfish
Starfish reproduction
Starfish reproduction begins when the right environmental conditions are met. Most of them reproduce during the warmer season. Many also choose the days of high tide. But how do starfish reproduce? Their main type of reproduction is sexual and begins with the search for individuals of the opposite sex.
These marine animals have separate sexes, that is, there are males and females, with some hermaphroditic exceptions. [1] Following the trail of hormones and other chemicals[2], are added in the most suitable places to reproduce. All species form more or less large groups called “spawning aggregations” in which there are males and females. From this moment on, each species shows different mating strategies.
How do starfish mate?
We already have plenty of stars gathered at the best possible time, but how do starfish reproduce? Most of the asteroids come together in very large groups and begin to crawl over each other, touching and intertwining their arms These contacts and the secretion of certain substances cause the synchronized release of gametes by both sexes: females release their eggs and males their sperm.
The gametes unite in the water and an external fertilization takes place This is how the starfish's life cycle begins. There is no pregnancy, but rather the embryos form and develop in the water or, in very few species, on the body of the parents. This type of mating is called pseudocopulation, since there is physical contact but no penetration.
In some species, such as the sand star (Archaster typicus), pseudocopulation is carried out in pairs. A male stands on top of a female, sandwiching her arms. Seen from above, they look like a single ten-pointed star. They can stay like this for a whole day, so much so that they are often covered by sand. Finally, as in the previous case, both release their gametes and external fertilization occurs.[3]
In the latter case, although mating is done in pairs, they also aggregate in groups. In this way, they increase their chances of reproducing, as well as having several partners throughout the same reproductive season. They are, therefore, polygamous animals
Is the starfish oviparous or viviparous?
Most of the starfish are oviparous From the union of the released sperm and eggs, a large number of eggs. Normally, they are deposited on the bottom of the sea or, in very few species, in incubator structures that have their parents on the body. When they hatch, they don't appear the stars that we all know, but planktonic larvae that swim adrift.
Starfish larvae are bilateral, that is, their bodies are divided into two equal parts (like us). Its function is to disperse throughout the ocean, colonizing new places. As they do so, they feed and grow until it is time to transform into adults. To do this, they go down to the bottom of the sea and undergo a metamorphosis process
Finally, although it is very rare, we must mention that some species are viviparous This is the case of Patiriella vivipara, whose offspring develop inside the gonads of their parents.[4 ] In this way, when they become independent from them they already have pentameral symmetry (five arms) and live at the bottom of the sea.
This is how starfish reproduce sexually. If you want to know in more detail the life of their larvae, their development and their metamorphosis, don't miss our article on How starfish are born.
How do starfish reproduce asexually?
There is a widespread legend that starfish can make copies of themselves by dropping one of their little legs. But is this true? How do starfish reproduce asexually? Before we know it, we must talk about autotomy.
Sea star autotomy
Starfish have the ability to regenerate lost arms When an arm is damaged in an accident, it can be detached. They also do it, for example, when a predator is chasing them in order to entertain it while they escape. They then begin to reshape the missing arm, a very expensive process that can take several months.
This mechanism also occurs in other members of the animal kingdom, such as lizards, which lose their tail when they feel threatened. It is called autotomy and is quite frequent in some starfish, such as the incredible sun star (Heliaster helianthus).[5] In addition, it is a process essential for understanding how starfish reproduce asexually.
Asexual reproduction of starfish
Some species of asteroids can regenerate their entire body from a severed arm, though only if it retains at least a fifth of the central disc. Therefore, the arms are not detached by autotomy, but due to a fission or fragmentation process of the body.
As we know, starfish have their bodies divided into five equal parts. Not only do they have five legs, but their central disk is also pentamerous. When the necessary conditions are met, this central disc breaks or splits into two or more parts (up to five), each with its corresponding legs. In this way, each part can regenerate the missing areas, forming a whole star.
Therefore, the newly formed individuals are identical to their parent; It is a type of asexual reproduction. It has not been possible to document all asteroid species, but it has been found in many of them, such as Aquilonastra corallicola [6]
Now that you know how starfish reproduce, you may also find it interesting to know What do starfish eat?
