Jellyfish are undoubtedly wonderful animals with characteristics that make them unique within the animal world. They belong to the Cnidaria phylum and their main feature is their gelatinous, bell-shaped body with a single body cavity, from whose lower end tentacles come out that have specialized cells called cnidocytes, which are stinging and provide protection against possible predators.. These animals are characterized by having two phases during their development, one of which is attached to the substrate, the polyp, and the other is free-living, called a medusa.
Have you ever wondered how jellyfish are born? If so, continue reading this article on our site where we will tell you everything about the life cycle of jellyfish and their development.
Do jellyfish lay eggs?
In general, all species of jellyfish have separate sexes, that is, they are dioecious and release their gametes into seawater when reproducing sexually. Once released, fertilization occurs, where the sperm will fertilize the ovules and these will be the eggs that the female will take care of between her tentacles to incubate them, so jellyfish are considered oviparous
However, there are species where the same individual has both sexes, that is, they are hermaphrodites, so they themselves release the two types of gametes to the outside, without the intervention of another individual. Discover all the details in this article about the reproduction of jellyfish.
On the other hand, these animals can reproduce asexually, through strobilation, a process that we will explain later, and through which buds are formed from which small jellyfish will be born.
As we will see, jellyfish have alternation of generations, being able to have two phases during their biological cycle, one as a polyp and another as a medusa. In short, the birth of jellyfish is a fascinating process because there is no single model.
How are jellyfish born?
The reproductive cycle of jellyfish is characterized by alternating generations. This means that, on the one hand, there are sessile polyps with asexual reproduction and, on the other hand, free-living and pelagic jellyfish with sexual reproduction. Next, we will see it in more detail.
Jellyfish eggs are hatched between the mother's tentacles. After its development, a larva called a planula is born This larva, when it is ready to become independent, floats away from its mother free-floating. After a few days, it descends until it finds a place to adhere to the seabed, and it is at this moment that it becomes known as polyp It is at this stage that the metamorphosis and its shape changes, becoming ciliated and cup-shaped with a suction cup that allows it to adhere to the seabed.
During the polyp stage, the jellyfish looks similar to a sea anemone. The polyp feeds on plankton as it slowly matures. Later, when the time comes, the polyp reproduces asexually, forming a colony of small polyps, which arise from the trunk of the parent. New members of the colony develop tubes through which they can feed. This phase will be maintained depending on the conditions of its environment, since it can last from days to several years if the conditions are not favorable. Then, the next phase of development consists of the dissolution of the colony and that is when hundreds to thousands of miniature jellyfish, that is, the young of the jellyfish.
How many babies can jellyfish have?
Depending on the species, jellyfish are capable of laying hundreds of eggs, from which small planular larvae will emerge. As we explained, its life begins between the tentacles of its mother, and then it begins to swim freely until it finds a place to settle. The polyp will then feed and grow into an adult jellyfish. The number of offspring is not defined and, as we said, they can lay hundreds of eggs, some studied species lay close to 500, although only a small percentage manages to develop.
Birth of jellyfish by type
These wonderful and unique animals, as mentioned above, are classified within the Cnidaria phylum. They are characterized by having stinging cells called cnidocytes, which allows them to defend themselves against predators or if they are disturbed. In the case of jellyfish, unlike other species, the cnidocytes are found in their tentacles, which allows them to kill their prey before they are digested.
The term medusa is used to refer to hundreds of species that in turn are classified into three large classes, all with polyp shapes and jellyfish, although with some differences regarding their birth. Next, we show these particularities regarding their birth, but if you want to know more about the types of jellyfish, do not miss this other article.
Hydromedusae or hydrozoans
This class is made up of both freshwater and seawater species and have alternation of generations, where there are asexual and benthic polyps and, on the other hand, planktonic and sexual jellyfish In many species it is common for polyps to form a colony where some individuals can develop both sexually and asexually. In addition, the entire colony is covered by an exoskeleton made of chitin.
Unlike the other classes, hydromedusae differ in that they have a mesoglea, which is a structure made up of a gelatinous mass that separates the layers of epithelium and is devoid of living cells, so which is usually made up of collagen. On the other hand, they do not have cnidocytes in the skin of their stomach, that is, in the gastrodermis, but they are present in the tentacles, which have a powerful poison.
These species form colonies where each hydroid fulfills a specific function, so you can find those in charge of digestion, called gastrozoids, and those that will be in charge of defending the colony, called dactylozoids and they are found in the tentacles, and the gonozoides, in charge of the reproductive functions. A particular detail is that each gonozoid produces asexual polyps that form sessile colonies, which will transform into sexual jellyfish.
Scyphomedusae or scyphozoa
Representatives of this class are the best known and are immediately associated with the name jellyfish. Here are the largest species, such as Cyanea capillata, which can reach almost three meters in length including its tentacles, as well as very small jellyfish that barely reach 2 cm in length.
This class is characterized by having the very short polyp stage, so they spend most of their life time in jellyfish phase. They reproduce sexually by producing eggs, from which a planula larva will develop. The larva grows until it is ready for strobilation to occur, but what exactly is it? Strobilation is the process by which, through transverse fission, small jellyfish called ephyra are originated, which will grow until they become adult jellyfish.
The transverse fission of these jellyfish consists of the division of a kind of superimposed discs, all of them with the same DNA. It is a type of asexual reproduction, so each disc released is an ephyra that, in a short period of time, will transform into a small jellyfish that will grow until it reaches the adult stage, at which point its biological cycle is complete.
Cubomedusas or cubozoos
Class formed by species distributed in the Philippines, Australia and other tropical regions. They are also known as sea wasps, a name that derives from their dangerous poison present in their tentacles, which is injected through the nematocysts of their tentacles, a structure that, like a harpoon, inoculates the toxin into its prey.
They are characterized by having a veil, a structure that resembles the veil present in hydromedusae. In hydromedusae, the veil is a fold of tissue located below the umbel (structure where the mouth is located below, it is concave and gives it the shape of a bell) that separates the internal part from the external part. In the case of box jellyfish, the wake is a structure that intervenes in digestion.
In addition, box jellyfish have rhopals, sensory organs that act as eyes that allow them to orient themselves thanks to the presence of photoreceptors in them. They are cube-shaped, hence the name of their class, and a very characteristic blue color. In this class strobilation does not occur during reproduction, and through studies it is known that some species can copulate and that only one jellyfish emerges from each polyp after metamorphosis.
