Class Scyphozoa
The class Scyphozoa can be found in the phylum of Cnidaria, the phylum of the “stinging” creatures, such as jellyfish. There are approximately 200 species that belong to the class Scyphozoa, and they are the most familiar of the gelatinous creatures of our world. These include, sea nettles, moon jellies and jellyfish. The jellyfish found in this class are dubbed "the true jellyfish". Many people associate the Portuguese Man-of-War and other well-known jellyfsh-like creatures with these Scyphozoans. However, in fact, the Portuguese Man-of-War and these other species are not "true" jellyfish. Yes, they have sac shaped bodies and long tentacles that sting painfully, but they are still structured differently than those organisms of Class Scyphozoa. And, hence, they are not "true" jellyfish.
Habitat
Scyphozoans are found in all oceans from the cold Arctic to the warm tropical waters of Caribbean. However, the majority of these species are located close to the equator in the warm tropical and subtropical waters of the Caribbean Sea, the Atlantic Ocean, the Pacific Ocean, and the Indian Ocean. This is why you can see jellyfish washed up along the shores of the beaches in Florida and other hot, tropical areas.
General Description
All Scyphozoans exhibit radial symmetry in their physical structure. This means that all body parts come from a central area. For example, the tentacles of a jellyfish usually encircle the mouth, which gives the organism a symmetrical appearance. Although Scyphozoans share physical characteristics, they greatly vary in size. They can be as small as twelve millimeters in diameter and can grow to have a diameter length of more than two meters. These jellyfish are invertebrates, which means they have no backbone like humans. In fact, jellyfish have no head, brain, skeleton or any organs used for respiration and excretion. They have a sac shaped body with one mouth opening that is surrounded by long tentacles. The body is composed of two main layers: the outer epidermis and the inner gastrodermis. These two layers are separated by a layer of a jelly-like substance called mesoglea. The tentacles, the most famous body part of the jellyfish, are covered with nematocysts, the stinging organs. These nematocysts contain toxins that allow the animals to stun and capture their prey, and keep predators away. The tentacles of a Scyphozoan can be extremely long, and can reach up to forty meters in length!
The structure of their bodies separate Scyphozoans from "fake" jellyfish. A Scyphozoan is one, single organism with two layers: the outer epidermis and the inner gastrodermis. But, "fake" jellyfish, such as the Portuguese Man-of-War and other Hydrozoans (organisms of the Class Hydrozoa) do not contain these two epidermis layers, and instead, are comprised of many individual organisms called polyps. Therefore, one single organism of a Portuguese Man-of-War is actually a colony of many individual polyps that work together to survive.
Aurelia aurita, moon jellyfish. http://www.photolib.noaa.gov/reef/reef2547.htmFlorida Keys National Marine Sanctuary
Reproduction
During its life cycle, a Scyphozoan goes through two different body forms, the most common form, medusa and the smaller form, larval stage. Jellyfish are male or female. The male jellyfish's reproductive organs develop in the lining of the gut. To reproduce the male releases sperm through its mouth into the mouth of the female, which will fertilize the eggs inside of her. The embryonic development begins inside the female jellyfish and she releases swimming larvae from her mouth into the water column. The larvae attach themselves to the sea bottom where they become polyps. They then divide creating new buds and jellyfish. In a few weeks the young jellyfish will grow into an adult medusa. The jellyfish live for only a short period of time – three to six months. This type of jellyfish can either be pelagic (lives in the water column) or attached to the sea bottom, and every other generation will be asexual.
Quiz- Multiple Choice
1. Which of the below is the correct order of stages in the life cycle of a jellyfish?
a) Larva-Medusoid-Polyp
b) Polyp-Larva-Chrolym
c) Larva-Polyp-Medusoid
d) Chrolym-Larva-Medusoid
2. Which pair of the following body parts does the jellyfish use to stun and capture
their prey?
a) Mouth and Tentacles
b) Tentacles and nematocysts
c) Nematocysts and Mesoglea
d) Salt from the ocean and mouth
3. Where can jellyfish be found?
a) In all of the world's main oceans
b) In only salt water lakes
c) In all fresh water ponds, rivers and streams
d) All of the oceans, except the Arctic Ocean and salt water seas, closer towards the
equator
Answers: 1. c. 2. b. 3. d.
Information on the Internet
- Sea Science This is a great website for an overview of the structure of jellyfish, its life cycle, and some background information on several specific species of jellyfish.
- Jellyfish - Wikipedia, the free encyclopedia Another excellent site that provides general information on jellyfish, as well as, many links to specific species, certain body parts and structures and great diagrams and high quality photos!
- Lifespan - Jellyfish An informative site that provides safety tips and advice on what to do when stung by a jellyfish.
- AquaFacts: Jellyfish A great site that answers the most common questions about jellyfish and provides some fun trivia about these unique creatures!
