Jellyfish are aquatic animals that are grouped within the cnidarians, a name that refers to a type of cell known as a "cnidocyte", from which a structure capable of inoculating a toxic substance that it varies in composition and intensity according to the species, being used for the defense and hunting of these animals. Most of these invertebrates live in marine waters, however, a few species develop in freshwater bodies, and in this file on our site we will talk about one of these species.
Do you want to know all the characteristics of the freshwater jellyfish? Its scientific name is Craspedacusta sowerbyi and it lives in different regions of the world. Keep reading and discover with us what its habitat is like, what it feeds on and what its bite is like.
Characteristics of freshwater jellyfish
The main characteristics of the freshwater jellyfish are the following:
- Taxonomically it is located within the subphylum Medusozoa and the class Hydrozoa. Thus, despite the name given to the species, they are not considered true jellyfish because the latter are grouped in the class Scyphozoa.
- It has no head or skeletal structure, as it is an invertebrate animal. It also does not have differentiated organs for respiration or excretion, but instead has a single orifice for eating and excretion.
- Over 90% of the body is made up of a water-based jelly-like substance.
- When it is an adult it has bell-shaped, although it is also somewhat flattened compared to other jellyfish.
- Around the bell there are some 400 tentacles of different lengths, solid and loaded with nematocysts, useful for hunting food and defending themselves.
- The digestive or stomach structure known as the manubrium is located towards the center and below the animal, where there is also the only opening that we have already mentioned that it has, through which the food enters and the excreted residues leave.
- There is a circular canal that borders the bell and four radial canals, the latter connected to the stomach area and which facilitate the transport of nutrients.
- It is common to observe the four gonads (genital glands) associated with the four radial canals, which differ according to sex as they are dysmorphic animals.
- On the edge of the bell are structures called statocysts, which allow the jellyfish to orient itself and maintain its balance.
- In the tentacles there is a tissue known as "eyespots", through which it perceives light, darkness and generally detects food and possible predators.
- The diameter of an adult freshwater jellyfish can be around 2.5 cm and the body mass can range 3 to 5 g.
Freshwater Jellyfish Colors
One of the easiest ways to identify jellyfish species, aside from their distinctive sizes and shapes, is by their colors. The coloration of the freshwater jellyfish is whitish or greenish, and the gonad area is usually shown as more opaque than the rest of the body.
Freshwater jellyfish habitat
The freshwater jellyfish was identified and described in England towards the end of the 1800s, however, it is native to China, specifically from the Yangtze River Basin. It is currently found on all continents except Antarctica, due to its introduction through trade between countries, such as ornamental aquatic plants.
The freshwater jellyfish is highly adaptable to various ecosystems of this type, but it seems to be more prevalent in spaces with calm waters and not with strong currentsThus, it is common to find it in freshwater lakes, natural or artificial reservoirs, areas of rocky quarries with the presence of water or ponds with algae.
In particular, the presence of the freshwater jellyfish has been reported throughout most of the United States and Canada.
Customs of the freshwater jellyfish
Commonly, the species is located towards the bottom of shallow bodies of water and does not usually move often, except to look for the food or escape from predation. It can be found alone or in colonial groups.
The Bloom of freshwater jellyfish usually occurs in the summer and fall months, with peaks around August and September. These population growths are mainly related to the increase in water temperature and the presence of food, which shows their preference for warm waters.
However, the freshwater jellyfish is somewhat unpredictable in terms of its presence and population development, since sometimes it does not respond to the aforementioned patterns, so scientists continue to study its behavior to learn more about it.
Freshwater Jellyfish Reproduction
Freshwater jellyfish generally respond to the reproductive cycle of this type of animal. A sexual phase, in which the female and male release their gametes into the water where they are fertilized. Subsequently, a larva is formed which, in this case, is called " planula". Then, this larva looks for a place at the bottom of the water, which can be on plants, rocks or roots, to attach, form hills and transform into the next phase known as " polyp ", which gives rise to a jellyfish yolk.
The jellyfish yolk is produced asexually because the polyp divides by budding and gives rise to an immature jellyfish, which will develop and will form an adult individual. But a peculiar aspect is that this species can also produce a bud known as " frustula", free-living and, although it cannot travel as much as the planula, it seeks another place to settle and cause another polyp formation. In other words, this phase called the frustula would be a kind of transition that the polyp uses to move to other spaces and continue reproducing.
On the other hand, the polyps of the freshwater jellyfish can enter a state of dormancy when conditions are unfavourable, changing their shape because they contract. In this case they are called "podocysts", which, in turn, become passively transported on the legs of aquatic birds, in conglomerates of algae or aquatic animals in general. Then, when conditions are favorable, the podocyst is activated to give rise to the polyp again and continue with development.
The precise aspects of these phases are still unknown, and scientists continue to study to better understand these reproductive cycles in freshwater jellyfish. However, it is speculated that its massive worldwide diffusion may be due to this state of latency.
Freshwater jellyfish feeding
It is a predatory animal, which feeds especially on zooplankton and particularly on small crustaceans such as daphnia and copepods. However, given the opportunity, it can catch and eat small fish.
When prey touches the jellyfish's tentacle, the nematocyst is activated, injecting the toxic substance that paralyzes the victim. Then, using the same tentacle, the food is brought to the mouth to be digested.
Freshwater jellyfish sting
All jellyfish produce toxic substances, some even lethal to humans, others with a milder effect but which can still be painful or annoying. However, a particular aspect of this species is that It has not been proven that its nematocysts can penetrate human skin, so it would be completely harmless to people. Thus, it is a lethal predator for its main food source, but not at all harmful to people. In fact, it is even considered a jellyfish that does not sting for humans.
Conservation status of freshwater jellyfish
There are no evaluation reports on the conservation status of the freshwater jellyfish and, as we have mentioned, its population trend in water bodies is somewhat unpredictable, per or is not believed to be in any danger in this regard.
