Facts about the Jellyfish: Behavior, Diet, Life Cycle & More

2010-11-04

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Jellyfish

These amazing creatures have been around for millions of years, longer than dinosaurs. There are many types of jellyfish, including those that sting and those that don’t. They can be found living in all oceans of the world and in freshwater rivers and lakes. Most can be found living in shallow coastal waters and a few can live in depths of 12,000 feet. Below is more fun and interesting facts about the jellyfish.

Description

Jellyfish come in different sizes, shapes and colors. Body size can range from less than an inch to over seven feet in diameter and tentacle length can reach up to 120 feet. Many jellyfish appear clear, almost to the point of invisibility, while others are brilliantly hued. Colors include yellow, orange, red, blue and purple.

Jellyfish are mostly made of water; less than 5% is solid organic matter. They do not have bones, teeth, blood, a heart, a brain or, with the exception of the box jellyfish, eyes. However, they do have a simple nervous system that allows them to function.

Behavior

Jellyfish do not attack humans but some will sting if they come into contact with one. The severity of the sting depends on a few things, including the species of the jellyfish and the sensitivity of the person to its venom. Most cases are minor, but some have been known to be fatal.

Movement

Jellyfish have some control with vertical movement. Their underside closes like an umbrella, pushing water out from the hollow space, to propel their body forward. Despite this ability, they mostly drift in the water, depending on currents, tides and wind.

Diet

Jellyfish eat a variety of food, some that are too small for the human eye to see. They eat small plants, fish and crustaceans, fish eggs and even other species of jellyfish.

Predators

Predators include sea turtles, spade fish and sunfish. In Asia, certain jellyfish are consumed by humans and are considered a delicacy which brings in millions of dollars.

Life Cycle

Life Cycle of a Jellyfish (#1 larvae, #11 ephyra leaving the polyp, #14 medusa)

Jellyfish evolve from a dimorphic (two-shaped) cycle. The two body forms are the asexual polyp and the sexual medusa. The male in the medusa form releases sperm from its mouth into the water and some of the sperm will enter into the female’s mouth. Fertilization takes place in the female’s mouth and the eggs will remain there until they develop into larvae. The larvae will leave the mother, drift through the water and settle on the floor. They are now called polyps. Polyps reproduce asexually by budding. The buds, which resemble a stack of saucers, are individual “baby” jellyfish called ephyra that separate from the polyp and drift in the water. After a few weeks, the cycle is complete when the ephyra grows into an adult or medusa. (Click on image to enlarge)