jellies

Jellies, commonly called jellyfish, are free-swimming marine cnidarians belonging to the phylum Cnidaria. They are characterized by a gelatinous, umbrella-shaped body called a bell, trailing tentacles, and specialized stinging cells known as nematocysts. Jellies are found in oceans worldwide, from polar to tropical waters, and occupy a range of depths, from coastal plankton layers to the open ocean.

Most jellies experience a life cycle that alternates between a sessile polyp stage and a free-swimming medusa stage. The medusa is typically the sexual stage, releasing eggs or sperm into the water, while a planula larva develops into a new polyp. Polyps can reproduce asexually to form new medusae. Jellies feed on small plankton, fish eggs, and larvae, using nematocysts on their tentacles to capture prey.

Ecology: Jellies play multiple roles in marine ecosystems as predators and prey. They form blooms under certain conditions, influencing plankton communities and sometimes impacting fisheries. Their stings can range from mild irritation to life-threatening envenomation for humans, particularly from box jellyfish and Irukandji types in warmer waters.

Conservation and research: While many jelly species are abundant, some populations are affected by overfishing, coastal development, and climate-driven shifts in distribution. Jelly toxins are studied for medical and pharmacological applications.

Note: In everyday language, “jellies” may also refer to gelatin-based desserts, prepared from gelatin or plant-based gelling agents; this article focuses on the marine animals.