Phylum Cnidaria

General characteristics of the phylum Cnidaria (ni-da-ree-uh) are

• invertebrates - animals without backbones

• radial symmetry - central mouth surrounded by a ring of tentacles like spokes of a wheel

• sac like body filled with jelly-like material

• tentacles with stinging capsules called nematocysts

• no internal organs like a brain, heart, gills, kidney, or liver, and no blood either, and a simple nervous system or nerve net which receives and passes information to other parts of the organism. This is an important evolutionary advance over the sponge phylum.

9,000 species in three classes:

1. Scyphozoa

•  jellyfish (jellies or Medusae preferred names)

2. Anthozoa (flower animals)

• sea anemones
• true or stony corals
• soft corals (including sea fans, pens, and pansies

3. Hydrozoa

• hydroids
• Portuguese-man-o-war

Class: Scyphozoa

The Scyphozoans are the most familiar jelly animals - free swimming, bell shaped animals commonly known as jellyfish, but are not fish at all. The adult form is called a medusa. However, their life cycle includes a polyp stage.

The anthozoans, or flower animals, look like flowers or upside down bells on stalks when they are adults. The body of an adult anthozoan is called a polyp. Most do not swim. With their adhesive base, they hold on to seaweed or rocks and wait for food to come to them.

The hydrozoans can be either free swimming or stationary polyps. The polyp generation is more noticeable, often forming bushy growths on rocks, while the medusa generation consists of small, microscopic animals. They often form colonies of animals, the most famous of which is the much feared Portuguese-man-of-war.

Physical characteristics

The medusa form of sea jellies consists of two thin layers of cells covering the inner and outer surfaces of a saucer-shaped mass of non-living gelatinous material. They have stinging tentacles around the perimeter of the bell, four or more frilly feeding arms in the center surrounding a mouth which takes food into the body and then releases waste through the same opening. They have a primitive stomach and reproductive organs. They are 2% protein, 2% mineral salts, and 96% water. Not only are the jellies the first animals to have evolved neuron cells but they also have the first muscle cells and were among the first to develop weapons that discharge coiled darts of stinging poisons. Jelly size varies from a tenth of an inch to the lion’s mane which may grow to eight feet in diameter with tentacles one hundred feet long. The moon jelly is six to ten inches in diameter.

Reproduction

Individual jellyfish are either male or female. The eggs and sperm develop in gonadal areas within the body wall. The gonads are quite apparent in the moon jelly and appear like yellowish brown four leafed clover designs near the top of the body. Some eggs stick to the frilly mouth lips where they are fertilized by the sperm. Cell division results in an embryo which develops into a swimming planula larva which makes its way to a solid surface. Here it attaches itself and immediately starts growing into a polyp. Each polyp is able to reproduce new polyps by a process called budding, in which completely new polyps develop from the body wall of the original creature. The polyps in LIS overwinter in this form and in the spring separate into a stack of disc shaped structures which break away to become the baby medusa jellies or ephyra. These young grow very rapidly during the Spring and Summer to full adult size. The life cycle of a jellyfish is about a year.

Scientists call the life cycle found in jellies alternation of generations. This is because the medusa generation undergoes sexual reproduction and alternates with the polyp generation, which undergoes asexual reproduction. A colorful wall chart in the area shows this life cycle. Please note it is not to scale. Eggs, larvae, and polyps are much smaller than the medusa. Polyps can also be noted attached to the inner wall of the cylindrical tank. To see the polyp in action check out this video from Alvaro Migotto of the Universidade de São Paulo in Brazil. - http://vimeo.com/13496458

 Nervous System

The nervous system of a jellyfish is primitive compared with the complicated network of brain, spinal cord, ganglia, and nerve tracts found in the higher level animals. However, they do have nerve cells similar to ours, which form a loose network just underneath the outside body layer. Each nerve cell connects to at least one other nerve cell. There is no central processing center to receive and send out impulses. Instead, when the nerve cells are stimulated, impulses shoot off in all directions. It senses with its whole body. Nerve cells of the nerve net will eventually make contact with the muscle cells which will respond by contracting or relaxing the muscles.

A concentration of nerve cells around the margin of the bell act as pacemakers which set off impulses at fixed intervals of time and cause periodic muscle contraction without outside stimulus.

Detector cells, called chemoreceptors, can sense the presence of certain chemicals given off by their prey. This will stimulate the jelly to pulse and move more rapidly thus increasing their chances of tentacle/prey contact.

Touch receptors in the tentacles and mouth lips respond to direct touch.

Jellies also have balance receptors, tiny stone-like structures connected to a concentration of nerve cells. As a jellyfish swims, the stone contacts the nerve cells which signal the muscles to contract and set the animal straight.

Light receptors in many species help them distinguish between night and day. Many jellies move up and down in the water in response to a sensed amount of sunlight present.

Respiration

Jellies have no lungs or gills. The walls of their bodies are so thin that oxygen molecules pass directly from the water into the internal organs and the carbon dioxide molecules pass out the same way. They really breathe with their entire bodies.

 Movement

Jellyfish are moved by water currents in the ocean and by contractions of their own bodies. They are considered part of the plankton of the ocean: that is, those animals that drift or float passively in the water. The box jellies are an exception, they can see and steer. See the Journal of Experimental Biology (JEB) article, Vol 214, 2809-2815 on how Danish researchers tethered jellies and directed their flight response using light panels. http:// jeb.biologists.org/content/214/17/2809.full?sid=65f7b8be-a0ca-4aec-b47e-306e5b12c23ab47e-306e5b12c23a

They are also able to swim slowly through the water by contracting the muscle fibers in their body wall, which are regulated by the primitive nervous system. In many medusae, these pulsations serve to keep the animal in an upright position. In species such as the moon jelly, the swimming is related to feeding. As animals pulsate, water is filtered through the tentacles and their prey are captured. They do maintain their individual spaces -- almost never colliding.

Feeding and Digestion

Jellies have no intestines, liver, pancreas, or any complicated mechanism for the digestion of their food. They have a large mouth and stomach, centrally located, and digest their food. They get rid of any waste matter through their mouth very rapidly. They cannot afford to carry bulky food or waste products which would make it difficult for them to float.

The primary food of the jellyfish are the zooplankton of the ocean, small animals, often microscopic. In the Aquarium, we feed them a small brine shrimp, which we grow in our lab. Jellies will eat other jellies in the ocean, but when they are injured they seem to become prey to their own species.

To aid in capturing their prey, jellies use tiny stinging capsules called nematocysts which are located on their tentacles (over a thousand per inch). A nematocyst consists of a capsule with a trapdoor at one end, and contains a coiled and folded hollow thread or tube. When an animal touches the trigger, the trapdoor opens and the tube is everted (turned inside out) as it extends from the capsule. The whole event takes place in milliseconds. The nematocyst tubes of some stinging jellies pierce the victim’s skin and inject a paralyzing toxin. Scientists have found thirty different types of nematocyst tubes and methods of capturing prey.A colorful wall chart in the exhibit area gives more information about nematocysts and includes drawings of charged and discharged capsules.

Biologists call the nematocyst an independent effect. This means that each capsule brings about its own discharge without having to respond to a signal which passes through the nervous system. They are discharged by direct touch AND the presence of chemicals from the prey.

The nematocysts are special weapons which make it unnecessary for the jellies to be as fast or faster, stronger, or more clever than their prey. The toxins injected act quickly to paralyze or kill the prey, which soon ceases to struggle. It then can be drawn to the mouth, swallowed, and digested without difficulty or damage to fragile body tissues.

As stinging capsules are used, others are developed to take their place. Jellies on the beach should also be treated with respect. Even though the animals is dead, the independently acting nematocysts can still sting on contact.

Predators

Two very large animals, the leatherback turtle and the ocean sunfish feed almost exclusively on jellyfish and most other turtle species do so during early life.

Loggerhead sea turtles find jellies a tasty treat, particularly the Portuguese Man-o-War. When currents bring huge numbers of jellies together, sea turtles will gather and gorge themselves in spite of their eyes being closed by the stings.

Sea slugs called nudibranchs feed on jellies without being affected by the nematocysts. In fact, it appears that the nudibranchs can move stinging capsules from the jellies, into their own body, thus equipping themselves with stolen weapons.

Humans are also a predator of the jellyfish, both for food and to eradicate them as pests. In some Asian countries dried jellyfish is considered a delicacy at $12.00 per dried disc.

 Effect on Humans

Most jellies cause mild or no discomfort to humans with their stings. The moon jelly in our exhibit is one of these. The other three are more troublesome, particularly the lion’s mane jelly. Many visitors will refer to the benign one as the white jelly of Long Island Sound and the stinging one as the red jelly.

Those that do effect humans severely have toxins which disrupt the synapses and stop transmissions of nerve impulses. Their enzymes cause searing pain. In addition, with some species there can be long term scarring and even death. Death can come directly as a result of the toxin or indirectly by drowning, because the toxin has immobilized the person.

The Australian sea wasp, a boxlike medusa about the size of a coconut, is the most deadly of the jellyfish. The venom of the sea wasp is said to be the most powerful and virulent poison in nature. It is one of the swiftest acting venoms, taking five minutes from sting to death, making it the most deadly known to science. Even when one part venom is diluted in 10,000 parts of water, it is still able to kill laboratory animals like mice and rabbits in seconds. Statistics from Australia indicate that 4-5 times more people are killed each year by the sea wasp than by sharks. An equally dangerous relative is the tiny Irukandji jelly found on the northern shore of Australia. “Irukanji Syndrome” is a delayed response (5-20 minutes) which is extremely painful.

In addition to jellies' adverse physical impact on humans, they also have an economic impact. They cost us losses of millions of dollars. A primary impact is on tourism. When the red flag goes up indicating that red jellies have invaded, tourists cancel their reservations. The sea nettle is a major problem in Chesapeake Bay, not only to tourism, but also to the fish and power industries. They clog water, burst nets, and limit possible activity in intake pipes and cooling systems.

Every attempt to control jellyfish - by nets, specific poisons or biological controls - has failed. Human pollution does not seem to bother them. In fact, sea nettles seem to thrive in waters over-nourished with sewage and Cassiopeia populations often explode in the polluted canals of the Florida Keys.

These pulsating parachutes have been around for 650 million years (from impressions in Cambrian sandstone found in Australia) and they will probably continue to thrive as long as the Earth has seas.

Aquarium Equipment

The “kreisel" tanks holding jellies are specially designed so that water currents keep the animals away from the glass walls and the intake/output systems. Everything possible is done to avoid damage to their delicate surfaces.

Degassing tanks have also been installed to remove gas bubbles from the water. If bubbles are left in the tank they can become trapped under the animals’ bells. If allowed to remain there, they can work their way into and through the animals’ bodies.

 Fun Facts

• When food becomes scarce a moon jelly (and many others) may lose over 90% of it’s weight. As food supplies become more abundant, it will gain much of that mass back.
• The immortal jelly can theoretically live forever. As conditions threaten, the medusa stage will metamorphose back to the polyp stage. When environmental conditions improve the polyp will again start to produce ephyra and buds.
• The largest migration in the world (as measured by biomass) takes place daily as the deep jellies rise to the surface at night to feed. As daylight approaches they again dive down to the protective dark depths.
• Engineers tell us the fastest thing/activity in the animal kingdom is the deployment of the stinger in a nematocyst -powered by osmotic pressure.
• The freshwater jellies, Craspedacusta sowerbyi, are an invasive species from China which are now found throughout North America. The stinger is “thought” to be too small to pierce the skin of humans and reportedly poses no threat.
• Jellyfish Lake in Palau, Micronesia is a marine lake which is home to golden jellyfish. These jellies make a daily migration “across” the lake to feed before retiring to the safety of the depths each night. No scuba diving is allowed - the bubbles, if caught in the bell of the jellies, would interfere with their daily travel and dinner plans!
•  First Aid - Vinegar! It’s standard equipment in Life Guard kits. It works by dissolving the cell membranes of unfired nematocysts. Doesn’t help with the pain but it stops things from getting worse.

Moon Jelly: Aurelia

Description: Medusa form of sea jellies consists of two thin layers of cells covering the inner and outer surfaces of a bell-shaped mass of non-living gelatinous material. They have stinging tentacles around the perimeter of the bell. There are four or more frilly feeding arms in the center surrounding a mouth. They have a primitive stomach and reproductive organs.

Color: Clear

Size: 6 to 10 inches in diameter

Life Cycle: The jellies life cycle involves an alternation of generation. The animal passes through two body forms. The animal begins in the polyp stage and then takes the medusa form as an adult.

Range: Throughout most of the world’s oceans.

Diet: Zooplankton. In the aquarium, we feed them a small brine shrimp. Predators: Sea turtles, ocean sunfish, sea slugs and humans.

Fun Fact: Jellies are 96% water.

Gallery 4.7 Jellies

Moon Jellies - You are what you eat! The “pink”colors of those 4 rings inside the bell are a pretty good indication dinner was brine shrimp.

Each nematocyst requires two triggers to fire. Both a mechanical touch and a chemical response. The bulb anemone shown here doesn’t sting the Maroon Clownfish (anymore). The juvenile clownfish brush against the anemone and acquire the protective chemical signature.

Phylum Ctenophora (ti nof’ ora

Leidy's Comb Jellies: Mnemiobsis leidyi

Small marine invertebrates with transparent gelatinous bodies and comb-like plates. They are found in Long Island Sound and throughout the world. Most are colorless and transparent as glass except for a beautiful iridescence of the comb plates.

There is a single opening at the oral or mouth end and a complex sense organ at the aboral end. Eight regularly placed longitudinal rows of movable comblike plates pass from near the aboral end to the mouth. Each plate is formed by the fusion of a row of large, powerful cilia. Swimming is accomplished by the beating of the comb plates in coordinated waves. The animal normally swims with the mouth end forward.

The Leidy’s comb jellies move forward with their mouth end open. When morsels of food enter the mouth, it closes and cilia move the food into the stomach. Other comb jellies such as the sea gooseberry, have long tentacles with numerous short branches.

Numerous cells, the colloblasts, are on each tentacle. The outer border of each of these cells is covered with tiny droplets of an extremely adhesive secretion to which any small animals stick. Periodically the tentacles are moved to the mouth where they captured prey is removed and ingested. Comb jellies do not sting their prey as the Cnidaria do.

They swim feebly by means of their comb plates but are often carried by strong water currents. Thus, they are planktonic.

All are carnivorous, devouring myriads of other small planktonic animals. Where they are abundant, they often sweep water clean of these animals, which affects small fish that also feed on them. They are eaten by fish.

Most comb jellies are luminescent, some exhibiting a nocturnal display of bluish or greenish light that is among the most beautiful in the animal kingdom.

They coordinate their activities through a primitive network of nerve cells, comparable in many respects to the Cnidaria. Although there is no centralization of nerve cells, the network is more connected under the comb plates.

Reproduction is sexual. A single comb jelly produces both eggs and sperm. Fertilization and embryonic development occur in the water. Development is direct with no larval stages.