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Home › Sea Life › Marine Biology › Invertebrates › Jellyfish

Interesting Facts about Jellyfish

[Jellyfish Phylum: Cnidaria] [Subphylum: Medusozoa] [Class: Scyphozoa (true jellyfish)]

Jellyfishes are soft-bodied, free-swimming, marine invertebrates. The lack of any bones or protective shell means the environment they live in actually supports their jelly-like symmetrical body.

This section contains interesting facts about "true jellyfish species", including where they live, what they eat, and how these umbrella-shaped creatures survive without a brain.

Jellyfish Habitats and Geographical Range

In general, the jellyfish species exists in most marine environments worldwide - including some saltwater lakes (e.g. the Jellyfish Lake in Palau).

Even though most of the two thousand (2,000) jellyfish types live in warm tropical open oceans, some can survive in ice cold water (e.g. the Antarctic regions).

Still, the preferred habitats of sea jellies are shallow inshore waters and deep underwater terrains. The hydrozoan species peach blossom jellyfish (Craspedacusta sowerbii) lives in freshwater.

Fun Fact: The jellyfish classification, known collectively as a "fluther of jellyfishes", actually belongs with the same taxonomy as corals and sea anemones (Actiniaria).

Jellyfish Characteristics and Behaviour

The most notable feature in almost all jellyfishes is the hollow bell - a round or arched 'canopy-shaped' dome that forms the upper body.

This mesoglea (hydrostatic skeleton) is made of a jelly-like substance. The mouth is located slightly below it near the trailing tentacles - which often contain nematocysts (stinging capsules).

Put another way:

As a consequence, almost all encounters with jellies create incredible photogenic opportunities, as they pulsate or drift "sluggishly" along with ocean currents.

Pro Tip: Another section contains more information about jellyfish anatomy and how their body system works.

What Do Jellyfish Eat?

Most jellyfishes are carnivorous. Hence, they feed on other invertebrates and microscopic zooplankton. They use specialised and venomous stinging cells (held within the tentacles) to "stun" or paralyse their prey.

After a victim has been immobilised with the poison, they use their oral arms to funnel the meal into the mouth.

The typical daily diet of a jellyfish can also include:

• Amphipods (known as scuds or side-swimmers)
• Copepods
• Crabs
• Krill
• Shrimp larvae
• Small fishes (including other sea jellies)

Pro Tip: Scuba diving around jellyfish increases the risk of being stung. Nonetheless, if you use caution and stay some distance away, they are fascinating and enchanting ocean marine creatures for watching and for capturing underwater photographs.

How Do Jellyfish Reproduce?

The complex life cycle of jellyfish involves two forms of sexual reproduction. It often includes two stages, the fixed-position "sessile" form (also known as the polyp form) and the adult or "medusa" stage.

Asexual Reproduction (Polyp Stage)

Some polyps reproduce asexually - either through a process of budding or by dividing itself into smaller segments (known as strobilation).

• Budding polyps can produce new polyps that can either remain attached by the stem or they can completely detach and form new individuals.
• In strobilation, the polyp segments into ephyrae - which are disc-like sections that form immature medusae. They eventually detach themselves and develop into adult medusae to complete the life cycle.

Sexual Reproduction (Medusa Stage)

Depending on the species, there are some adult jellyfish that release sperm and eggs into the water column. This process means fertilisation can either occur internally inside the female jellyfish or externally in the water.

Once fertilised, the tiny eggs start to develop into a free-swimming planula larva - a phenomenon copied by some coral species and sea anemones. The larvae eventually find a suitable surface to settle on and develop into polyps.

Types of Jellyfish Species List

7 Fascinating Facts about Jellyfish

Picture the most graceful and ominous creature floating in the ocean drifting with tidal currents and following the sun.

These seven lesser-known facts prove why the elegant jellyfish has more to offer than a transparent sac of gelatin and poisonous tentacles.

1. Jellyfish May Be 500 Million Years Old

Jellyfish may be one of earth's oldest species. They exist in most coastal and shelf waters - especially in temperate environments.

2. Jellyfish Use Toxic Nematocysts to Kill their Prey

Jellyfish use millions of tiny poisonous stinging cells (nematocysts) to capture their prey. But, if human skin makes contact with jellyfish tentacles the painful - and sometimes deadly - toxin is absorbed through the skin.

3. The Box Jellyfish is the most Deadly

The box jellyfish (Chironex fleckeri) is the most toxic species of all and found in Australia and some parts of the Indo-Pacific regions. The sting from this deadly jellyfish species is known to kill a human in less than five (5) minutes.

Box jellyfish toxins are excruciatingly painful and can often lead to human deaths from medical shock or heart failure. The box jelly has four (4) clusters of six (6) eyes (total 24) across its bell.

4. Some Jellyfish Don't Sting

Despite their infamous notoriety, not all jellyfishes have a poisonous sting. For example, the migrating golden jellyfish (Mastigias papua etpisoni) in Palau is nontoxic.

5. Jellyfish are Not Fish

Jellyfishes are invertebrates and related to sea anemones and corals. They are not fish. Jellyfish are brainless, heartless, boneless, and they do not have a spine.

6. The Lion's Mane Jellyfish is the Largest

The lion's mane jellyfish (Cyanea capillata) can grow to a diameter of almost three (3) metres with tentacles measuring over thirty (30) metres long. It is easily the largest of all jellyfish species.

7. The Smallest Jellyfish is the Most Deadly

The most fatally potent of all jellyfish is also the smallest. The sting of the Irukandji jellyfish (Common Kingslayer) is 1,000 times stronger than a tarantula spider.

Jellyfish Stings

Jellyfish tentacles can grow more than one metre in length and their transparency makes them almost impossible to identify underwater. Each tentacle contains a seemingly uncountable number of nematocysts.

So, how dangerous are jellyfish stings?

Nematocysts are stinging cells used to stun jellyfish prey. If you get stung, they cause excruciating pain, swellings, and severe irritation.

The most dangerous jellyfish species have developed stinging cells so powerful that they can seriously harm or cause death to humans.

Here's the thing:

Despite the potential danger, getting stung by jellyfish while scuba diving is relatively uncommon and rarely considered a major threat.

Jellyfish broadly drift in the upper levels of water close to the surface and the sting is harmful only if it makes physical contact with bare skin.

Therefore, sea jellies are more likely to sting swimmers, snorkelers, and beach paddlers than scuba divers.

Furthermore, scuba divers usually wear a protective wet suit and gloves which leaves little exposed skin. Despite this protection, you should always stay well clear of jellyfish if you spot them in the water.

Pro Tip: The most reputable dive centers and experienced dive guides will be cautious of any dangerous jellyfish in the water and will alert visiting divers to any seasonal invasion or local sightings.

Treatments for Jellyfish Sting

Some parts of a jellyfish are dangerous to humans. The stinging cells (nematocycts) are particularly menacing for several potentially fatal reasons.

Although some people tolerate mild stings better than others, some people suffer extreme reactions to a sting.

The sting is effectively a dosage of potentially life-threatening venom or poison. The toxicity is related to the species and affects people with differing symptoms and outcome.

The body's reaction to a sting is also related to the person's size and chemistry. Generally, smaller people will suffer more severe reactions with greater effects which may result in anaphylactic shock.

Typical Reactions to Jellyfish Sting

• Mild to severe pain
• Sickness and nausea
• Skin irritation and stinging
• Skin blisters and welts
• Respiratory problems or difficulty breathing
• Anaphylaxis or severe allergic reaction
• Cardiac arrest and death

Jellyfish stings should be treated immediately. Medical research centers and dive safety organizations both recommend using vinegar as the most successful initial treatment for a sting. Divers should use vinegar because it neutralizes the stinging nematocyst cells.

Applying liberal amounts of vinegar helps to reduce pain and minimize discomfort from the irritation. It also helps to slow or stop the venom from spreading around the body.

This immediate treatment is particularly important and potentially life-saving if the sting is by one of the most toxic species - such as one of the box jellyfish species.

Dive boats usually have vinegar on board or in the first aid kit. If you do not have vinegar available you may use salt water as a rinsing agent. Baking soda is also capable of neutralizing sting cells.

In case you were wondering...

Despite being in many a 'divers tale', urinating on someone's jellyfish stings is not an official recommendation by medical professionals.

Doctors also suggest that rinsing stings with freshwater may cause the nematocysts to fire and therefore should not be used.

Jellyfish tentacles are extremely sticky. They adhere to the bare skin and they should be removed after you have neutralized the stinging cells.

Use a razor to shave the affected area or scrape the tentacles free with a clean credit card or something similar.

You can also use tweezers to remove individual jellyfish tentacles. Remember to wear thick gloves to protect your own hands.

When recommended first aid supplies are not available, use hot packs or dry cold packs to reduce pain and sand may be used as an abrasive to scour the jellyfish sting area.

Apply hydro-cortisone cream if available and monitor the victim's breathing and reaction to the sting.

Important: In most incidents you should seek medical advice as soon as possible because the victim may require a shot of epinephrine or antivenin treatment.

Jellyfish Threats and Predators

A jellyfish has a soft gelatinous body which is usually a transparent sac and dangling tentacles. They may appear non-threatening, harmlessly drifting with tidal currents.

The body might appear to be unprotected. Even so, and despite their perceived vulnerability, the majority totally avoid being eaten by their predators and survive to reach full maturity. They protect themselves from harmful attacks by their tentacles.

By and large, most of the jellyfish species are not currently listed as endangered or threatened. But, the conservation status often varies according to different regions.

Even though jellyfish blooms increase where overfishing and climate change reduces their natural predators, such as sea turtles and the ocean sunfish (Mola Mola), other notable threats include underwater garbage pollution and habitat destruction.

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