Simple Marine Organisms – Jellyfish
Jellyfish Basics
· Jellyfish are not fish nor do they taste good with peanut butter . Rather, they are primitive (they have been around for >500 million years ), gelatinous animals with stinging tentacles and one body opening.
· Jellyfish and their relatives- including coral polyps and sea anemones - are in the phylum Cnidaria . Cnidarians are characterized by their ability to sting their prey with structures called cnidocytes .
Cnidocyte Structure
Before firing After firing
· Cnidocytes are tiny, one-use, automatic, barbed, harpoon-like structures designed for impaling prey. They generally contain venom for paralyzing and digesting their victims.
Anatomy of a Jellyfish
· A generalized jellyfish consists of a bell or hood , with tentacles hanging down.
· They are extremely simple organisms, 95 - 98% water, one body opening that acts as both their mouth and anus , and no central nervous system.
· Most do have light sensing structures called eye spots, and a nerve net , for coordination and movement.
Life Cycle of Jellyfish
· Jellyfish can reproduce both sexually and asexually. They reproduce sexually in the adult medusa form, and asexually, through budding in the juvenile polyp form.
· Although they are short lived- usually 3 - 6 months- some jellyfish can release upwards of 40,000 eggs daily!
· Their fast development, ability to reproduce both sexually and asexually , and massive egg production allows jellyfish to produce blooms- very large numbers of organisms in a short period of time .
Common types of Jellyfish
Cannonball Jelly
· Common along the east coast of the North and South America, these jellies are not especially venomous, and average 8 inches in diameter.
Moon Jelly
· Also found in the Atlantic along the eastern U.S., this slightly venomous jelly averages 8 – 10 inches across its bell. It can be identified by the four crescent moon shapes atop its bell.
Box Jelly
· This extremely venomous jellyfish kills more- many more- people than sharks do. It is found worldwide, but predominates in waters of the Indo-Pacific region.
Portuguese Man o’ War
· Not a true jellyfish, rather a relative that is a colony of organisms called zooids working together, this surface drifting jelly can have tentacles up to 165 feet long, deliver a painful, possibly deadly sting, and can occur in significant numbers in places around our Atlantic and Gulf coasts.