Jellyfish are dioecious and have reproductive glands near the gastric sac. Mature spermatozoa flow into the female jellyfish for fertilization. Fertilized eggs develop into larvae that leave the mother's body and swim in the water for a while before sinking to the bottom to form ? mouth larvae, which later become transverse schizothoracic, transverse schizothoracic split into multiple disk-shaped larvae, which then develop into jellyfish adults.
Jellyfish belong to the phylum Coelenterata, the mantle jellyfish. Jellyfish is composed of an umbrella-shaped gelatinous material body, there are many tentacles underneath, through the umbrella of muscle contraction, jellyfish can swim on the surface of the sea together with the ups and downs. Because the jellyfish's internal cavity is connected to the outside world through its mouth, this group of animals used to be called coelenterates, but now they are called cnidarians. The tentacles of the jellyfish are full of stinging cells, which release coiled filaments to entangle food when stimulated, and some have barbs or spines at the end of the stinging cells, which inject venom into the prey to anesthetize it. Small holes in the ventral center of the mouth or mouth channel prey on zooplankton. The tentacles on the rim of the umbrella have as few as four and as many as hundreds.
One species of monkshood jellyfish, also known as the Portuguese Battleship, looks like a jellyfish in appearance, but it is actually a group of jellyfish and hydroids combined. The tentacles have stinging cells that can anesthetize large fish and can cause damage to humans as well.
In the North Atlantic, there is a class of jellyfish, the diameter of up to 4 meters, tentacles up to 30 meters long, can be considered the world's largest jellyfish.
Jellyfish are mostly found in the sea, except for a few that live in freshwater; many of them are often harmful to tourists in the bathing beaches. Jellyfish can reproduce both sexually and asexually. The jellyfish we usually eat is a kind of jellyfish.