Fascinating Facts About Jellyfish

The gelatinous beings gliding, bobbing, and drifting in our mighty oceans for more than 500 years are jellyfish. From warmer tropical waters to colder seas and even along coastlines, jellyfish can propel along ocean’s currents anywhere. Some species can even be found enjoying an underwater salad party in freshwater!

In this fin-tastic article, we will dive into the realm of jellyfish and find out some facts about jellyfish that make them so fascinating.

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Jellyfish Jamboree: A World of Wobbly Wonders!

Jellyfish, also called sea jellies, fall under the phylum Cnidaria.

Jellyfish are clear mysterious sea creatures. They seem fascinating, and mystifying when in the water. But when you take it out of the water, it readily transforms from a mystic sea creature to a less appealing blob. It’s because a staggering 95% of the body of a jellyfish is made of water. Isn’t it a squishy surprise?

But the ultimate thing that would blow you away is that these critters don’t have brains, blood, or even hearts.

Instead, they are made of three layers:

The outer layer is called the epidermis
The thick and highly elastic middle layer is called mesoglea, and
The inner layer is called the gastrodermis.

They don’t have highly developed organs for digestion. Rather, they use an elementary nervous system called a nerve net to react to different stimuli – sniffing out smells, tracking light, hunting their prey and getting into their watery wonderland!

Their digestive system (or better called a cavity) is a truly multitasker. Can you imagine this small cavity has a single opening for munching and disposal and acts as both its stomach and intestine? – efficiency at its finest!

From pelagic zones to deep-sea trenches, these versatile creatures can be found thriving anywhere.

Jellyfish aren’t picky when it comes to their food. Their menu ranges from plankton to small fishes; jellyfish feast on almost anything. Most of them are carnivorous.

The food habit of this mystic oceanic creature is no less than a tapestry mainly driven by its size. Some are as small as a pinhead that they cannot but feed on floating planktons. Don’t get bewildered if you see big jellyfish enjoying a banquet comprising crabs, sea turtle, shrimp, or even other small species of jellyfish!

Types of Jellyfish

Sea jellies are categorised into four groups based on their physical attributes. classify organisms based on physical characteristics. Of the thousands of species of jellyfish, there are four main groups:

Scyphozoa: In the whimsical oceanic realm dwells Scyphozoa – a group of 400 medusozoa. They are better known as the “true jellyfish” because of their medusa-like big bells. Their irresistibly charming bells exhibit radial symmetry – meaning, their shape is the same around the central axis. You can often notice them in their medusa body form.

Hydrozoa: The denizen of hydrozoa houses more than 3,800 species. From undersea dwellers to swimming groups – you just can’t count them. Freshwater jelly (Craspedacusta sowerbyi), Portuguese man of war (Physalia physalis), etc. are examples of hydrozoa.

Cubozoa: Better known as “box jellyfishes”, these marvellous sea creatures look similar to “true jellyfishes” but with big box-like bells. What makes them stand out from the pack is their lightning-fast swimming. They can navigate around obstacles and have a comparatively developed nervous system with eyes with lenses, corneas, and retinas. This implies that they have comparatively better eyesight even though they have no brain – believe it or not. Around 48 species fall into this category who love warmer tropical waters as if they were enjoying a sunny seaside getaway! Example: sea wasps (species in the genus Chironex).

Staurozoa: Like other sea jellies, the jellyfish under this category love clinging to seaweed or rocks rather than pulsing and navigating through the currents in the ocean. You will find around 50 sporozoan species thrive in the seawater, mesmerising onlookers with their whimsical combination of beauty and camouflage.

From Polyp to Medusa: The Lifecycle of a Jellyfish

The translucent body of jellyfish that occasionally sun bask on the sandy coastline may mesmerise you. But do you know how they undergo a range of steps to look the way you like?

Let’s go through the lifecycle of these oceanic tentacular twirlers.

Life begins – the egg

It’s the beginning of the life of a jellyfish when an adult male sea jellyfish finds a chance to meet with an adult female jellyfish. Medusa, during spawning events, accumulates in the ocean in large numbers during dawn or dusk. The females release eggs and males sperm in large quantities in the water column. The spawning events of jellyfish are triggered by a slew of factors – availability of light, food, and other sea jellies. The bigger the medusa can get, the better their chance to reproduce.

While the fertilised eggs usually float along the ocean current, some jellies such as moon jellies brood their eggs on their oral arms until they get into the next phase. This nurturing process deems a warm hug to the would-be offspring that increases their survival possibilities.

Jelly babies – planula larva

In this phase, the internally fertilised eggs transform into a free-swimming planula larva. The jelly babies, in this phase, look like microscopic flatworms embellished with cilia – small tiny hair in jelly babies. This little hair twirls in sync, allowing the minuscule critters to drift along the current and float in the sea depth.

In this phase, baby jellies set off their magical underwater journey! They start finding their home-sweet-home – the most favourable habitat to settle down.

Most often, they cling to or near seabeds to grow into polyps. On the other hand, some larvas are bizarre with their habitats – they love to build a unique partnership with other sea creatures, mainly adult jellyfish, by finding their home on their bodies! Welcome to the strange, bustling underwater world!

The Childhood: Polyps

Once the planula gets its footing, it starts transforming into polyps – the longest phase of a jellyfish’s life cycle.

That said, for most of us, jellyfish is a slimy gelatinous medusa that washed up on the beach but throughout most of its lifetime, a jellyfish dwells at the bottom of the ocean as a polyp with its one end hooked to the seafloor, and the other end unfurling into the water with a ring of tentacles encircling its mouth/anus. By this stage, their digestive system gets well developed and they can hunt down their prey to feed on by themselves.

As the polyp grows, it starts segmentation and reproduces asexually to generate its clones. How long this polyp stage continues depends on the species of the jellyfish. For some species, it can be years until they get an optimal environment to spawn before they step into the medusa phase of their life.

Budding teenagers – scyphistoma

In this stage, the segments a polyp generates develop horizontal grooves to bud off a new baby jelly from its stalk ends. This process is called strobilation and the strobilating polyp is known as a sessile polyp or scyphistoma. These new baby jellies eventually grow into new male or female adults. Do you know that some species of jellyfish can change their sex with time?

Finding themselves – ephyra

The grooves that are budded off the top ends of the scyphistoma are called ephyra. They are free-swimming baby jellies that don’t have a developed round bell; instead, they have arm-like bumps. As they grow, these protrusions develop into full translucent and round bells. This is when they segue into the medusa stage.

The Matured Jellies: Medusa

As Ephyra heads toward the medusa stage, it starts showing its oral arms and tentacles that take different shapes and sizes based on the species the jelly belongs to.

Medusa is an adult jellyfish capable of reproducing their offspring. However, the reproduction rate varies and depends on a slew of factors depending on the species, for example:

Moon jellies or compass jellies, when it comes to reproduction, need to be bigger and larger in numbers compared to their rivals for successful reproduction. The bigger the jellyfish, the more eggs and sperm they can release, which, in turn, gives them a competitive advantage when it comes to passing their traits to the new genes.

But are there any amazing jellyfish facts?

Fascinating Jellyfish Facts for Kids

Let’s go through some amazing facts about jellyfish:

Time-Travelling Jellies: Dino-Dwellers of the Ocean!

Do you know that jellyfish – one of our gentle ocean pals – have been drifting along the ocean currents for more than 500 million years? Jellyfish inhabited the mighty seas long before dinosaurs tramped the Earth!

Not-so-fishy Invertebrates

How did they get the “word “fish” with their name? It’s an unsolved riddle! The fact is that jellyfish are not fish at all. They are invertebrates of the whimsical oceans falling into the phylum Cnidaria!

Jellyfishes’ Size Parade Under the Sea

Another interesting fact is their varying size. From tiny critters to massive gliders, jellyfish have thousands of species in its realm. These species vary in size and shape – from a few millimetres to several metres. These stingers of the sea are going to blow you away!

The Hunting Prowess of Jellyfish

Many species of jellyfish sport tentacles with their stinging cells. These jellyfish stings are called nematocysts. They use these tentacles to stun their prey to feast on. Based on the species, the number of tentacles varies, for example, a lion’s mane jellyfish can have up to 1,200 tentacles lined up in eight clusters.

Some species are venomous that can paralyse or even kill their prey. Be aware of these venomous creatures as jellyfish stings – the occourance when the stinging cells in their tentacles come in contact with skin and inject venoms. Jellyfish stings can be painful or can result in irritation, depending on the jellyfish species.

Some Jellyfish can Turn the Clock Back!

Yes, you have heard it right! Some jellyfish are biologically immortal. An example can be Turritopsis dohrnii, an immortal jellyfish, thriving in the temperate to tropical waters. If hurt, hungry, or in a severe environment, these jellyfish can drop to the seafloor and revert to polyps from medusas – thus, eternalising its cycle of immortality.

Wrapping Up Jellyfish Facts!

Jellyfish – both as prey and predators – play a critical role in the aquatic food web and balancing aquatic ecosystems. For example, by feeding on plankton, and other living organisms, they regulate their population in the sea.

Again, while drifting through different water column layers, they transport nutrients such as nitrogen and phosphorus. That said, any anthropogenic activities, pollution, overfishing, etc., can significantly affect the number of jellyfish in the aquatic ecosystem. As a result, the balance of the ecosystem and the distribution of energy throughout the food chain can be affected.

Let’s keep the ocean habitable for jellyfish – our ocean buddies!