Cnidarians are those aquatic animals, mostly marine, that have stinging cells in the tentacles that all the members of this edge possess and that are injected into the creature that brushes them. They are one of the simplest animals that exist.
What is it?
It is an edge where you will find about 10,000 species of very simple animals, most of which live in the sea. Its name comes from the Greek κνίδη “kníde” which means nettle, this is because they have stinging cells known as cnidocytes, which are found in their tentacles and inject into the skin of any living being that rubs them.
They are a very old group of animals, their fossils are millions of years old and scientists have established that their ancestors belonged to the Ediacaran fauna, 600 million years ago.
New Age-based studies of their mitochondria suggest they inhabited the earth long before, some 741 million years ago.
Examples of cnidarians
Blue scale. Bad water. White jellyfish. Common jellyfish. Craspedacusta jellyfish. Giant jellyfish from Japan. Medusa fried egg.
Anemones
Actinia equina. Actinia fragrance. Aiptasia mutabilis. Commensal anemone. Warty anemone.
Polyps
Mirabeau. Solitary polyp of the Flabellum coral. Colonial soft coral polyps. Colonial hard coral polyps. Tubastraea.
Corals
Acropora cervicitis. Acropora palmata. Antipatharia. Antipathies. Dendrogyra Cylindrus.
General characteristics
Cnidarians have a series of specific characteristics that differentiate them from other living things: They have cells that are organized in two layers forming functional units. Some cells can be independent.
They are diblastic animals, they present epidermis and gastrodermis. Your body is organized like a sack and your digestive system has a single hole that serves as mouth and anus at the same time, they also use it to release genital substances into the water.
They have a gastrovascular cavity where they digest food and distribute it to the body along with oxygen, that is, it acts as the digestive system and heart.
This cavity also acts as an excretory system. In the cnidarians or coelenterates you will find several classes such as hydrozoans, sciphozoa, anthozoa and cubozoa. According to studies, all other classes come from the Antozoans, the oldest coelenterates.
The ectodermis is an external layer that protects the body and the gastrodermis is a light layer that limits the gastrovascular cavity. Between both layers is the mesoglea, very thin and which may or may not have cells depending on the species.
Some cnidarians have eye spots or ocean spots, which are small clusters of rodoxin-pigmented cells and hair cells that transmit sensory information to them. Some advanced cnidarians have ocelli, which have photoreceptor cells that allow them to capture light and shadow.
To know their position, they have statuses, structures formed by two types of cells, some sensory ciliates and others that have calcareous pellets called statolites, when the coelenterate turns, the statolith moves and brushes a sensory cell, thus informing the animal of their movements and position.
