Oldest Surviving Sea Animals That Exists Today

9 Oldest Sea Animals Still in Existence

The earliest life forms on earth originated in oceans billions of years ago. Marine life is full of diverse variety. They form a critical part of our ecosystem.

While most pre-historic sea animals became extinct as part of evolution, some still exist. These species have survived for millions of years despite all the other changes around them.

Scientists have confirmed their millions-years-old existence from fossils and found that these sea animals have shown minimal changes over the years.

Here we list 9 of the oldest surviving sea animals that still exist. 

9. Sturgeon

Estimated age: 174 million years
Phylum: Chordata
Class: Actinopterygii

Sturgeonphoto source: britannica.com

The name Sturgeon describes 29 species of fish of the Acipenseridae family. Many of these species are considered critically endangered. The oldest known fossil of sturgeon dates back to the Middle Jurassic age (174 to 163.5 million years ago).  

Sturgeon lives in temperate waters in Northern Hemisphere. Most species are native to the ocean and ascend rivers, while others live in freshwater. They are found in large numbers in the freshwaters of North America and the rivers of Russia and Ukraine. 

Did you know?

Sturgeon is believed to be evolved from a group of fishes known as palaeonisciforms, which appeared about 419 million years ago.

8. Tadpole Shrimp

Estimated age: 365 million years
Phylum: Arthropoda
Class: Branchiopoda

Tadpole Shrimpphoto source: wikipedia.org

Notostraca, commonly known as tadpole shrimp, is a living fossil that has remained almost unchanged for over 250 million years. Tadpole shrimps live on the bottom of temporary ponds and shallow lakes. 

They have a broad flat carapace at the front end and a longish slender abdomen. It gives them ­a shape similar to a tadpole and hence the name. Tadpole shrimps are found in freshwater, brackish water, shallow lakes, and moorland worldwide.

The oldest known fossil of tadpole shrimp is found in Belgium. It is of the species Strudops goldenbergi, which existed some 365 million years ago. 

Did you know?

Tadpole shrimp has a strange lifestyle. Its eggs blow about in the wind for decades and wait for the right moment to hatch. After being hatched, it grows quickly and reaches maturity within two to three weeks.

7. Coelacanth

Estimated age: 410 million years
Phylum: Chordata
Class: Sarcopterygii

Coelacanthphoto source: wikipedia.org

The coelacanth is a type of fish found near the Comoro Islands off the southeastern coast of Africa and Indonesia. The oldest known coelacanth fossils are more than 410 million years old. 

The coelacanth has two extant species: The west Indian Ocean coelacanth, also known as gombessa, and the Indonesian coelacanth. The former is listed as critically endangered by International Union for Conservation of Nature, and the other is listed as vulnerable. 

Both species look similar except for the background coloration of their skin. For Indonesian coelacanth, the coloration is brownish grey, and for West Indian Ocean coelacanth, it is bluish.

Once, it was thought that coelacanth was evolutionary conservative, but later research has found initial morphological diversity.  

Did you know?

The coelacanth was thought to have become extinct around 66 million years ago. Although gombassa was historically known to the local fishermen in Comoro Island, it was scientifically identified as coelacanth only in 1938.  

6. Greenland Shark

Estimated age: 450 million years
Phylum: Chordata
Class: Chondrichthyes

Greenland Sharkphoto source: wikipedia.org

The Greenland shark is one of the largest extant species of shark. It is closely related to the Pacific and southern sleeper sharks. The Greenland sharks can mostly be found in the cold depths of the North Atlantic Ocean and the Arctic Ocean.

However, based on recent research, scientists believe that at great depths, the Greenland shark’s range is probably extended to the Caribbean.

It is an apex predator, mainly feeding on fish and hunting as big animals as seals. Greenland sharks are slow movers; thus, they often hunt their prey asleep. It is known to be a scavenger and gets attracted by the smell of rotting meat.d

Greenland shark meat is edible but only after being treated for safe consumption. The process involves boiling the meat in several water changes, drying, or fermenting. Untreated meat is poisonous as it has a high concentration of trimethylamine N-oxide.  

Did you know?

Greenland sharks have the longest life span of all vertebrates. It is estimated that a Greenland shark can live up to 500 years.

5. Lamprey

Estimated age: 450 million years
Phylum: Chordata
Class: Hyperoartia

Lampreyphoto source: wikipedia.org

Lamprey is a fishlike jawless vertebrate. They live in coastal and freshwater and can be found in temperate regions, except in Africa. 

About 43 species of lampreys have been documented so far; among them, five species were declared extinct. Lampreys have a toothed funnel-like sucking mouth. The carnivorous species (about 18) infiltrate into the flesh of other fish and suck their blood with the help of this tubular mouth. 

Overfishing, construction of dams and other projects, and pollution are some of the main reasons for their decline. 

Did you know?

Non-carnivorous lamprey species do not feed as an adult. Instead, they survive on the reserves accumulated as larvae through filter feeding.   

4. Horseshoe Crab

Estimated age: 480 million years
Phylum: Arthropoda
Class: Merostomata

Horseshoe Crabphoto source: wikipedia.org

Horseshoe crabs have been around for 480 million years. Horseshoe crabs are not true crabs; they are more closely related to scorpions and spiders. The horseshoe crab got its name from its shape and anatomy. 

Horseshoe crabs represent one of the oldest extant groups of animals. They live near the shallow coastal waters of the ocean floor. Therefore, they are most often found in foreshore and spring high tides.

Their bodies are covered with a hard carapace. They use hemocyanin to circulate oxygen through their blood. Once, horseshoe crab blood was widely used in the pharmaceutical industry. The blood was harvested by collecting and bleeding the animals and then releasing them back to the sea. Most of the animals would survive this process.

Did you know?

The horseshoe crab is an endangered animal. A few species of horseshow crab have already been declared extinct. Horseshoe crabs face critical dangers of habitat loss, shoreline development, use for scientific research, and overfishing.     

3. Nautilus

Estimated age: 500 million years
Phylum: Mollusca
Class: Cephalopoda

Nautilusphoto source: wikipedia.org

Nautilus is called the living fossils. They have existed for over 500 million years and have remained relatively unchanged. The early examples were straight-shelled, as found in the extinct Lituites genus.

It is still not known precisely when they originated, but scientists believe they developed in the late Cambrian period. Later, during the Ordovician period, they became one of the major sea predators. 

Coleoidea, the other cephalopod subclass, branched off long ago, and since then, the nautilus has remained relatively unchanged. 

Did you know?

Nautilus has impaired vision; they can only distinguish between light and dark. However, their smell is overdeveloped, which helps them hunt prey. 

2. Jellyfish

Estimated age: Possibly 700 million years
Phylum: Cnidaria
Class: Scyphozoa

Jellyfishphoto source: YourPetyourLove

Jellyfish is the oldest multiorgan animal group. They have existed for at least 500 million years and possibly over 700 million years.

Jellyfish are found both in surface water and deep sea. Scyphozoans, or the “true jellyfish,” can only be found in marine water. However, some hydrozoans that appear like “true jellyfish” live in freshwater. 

Two types of scyphozoans are there: free-swimming medusae and sessile. Free-swimming scyphozoans can be found in oceans all over the woHowever; they usually live only a few weeks.  

Did you know?

Jellyfish can clone themselves. Their lifecycle includes a combination of sexual and asexual reproduction. When they are at the polyp stage, they can create several clones of themselves.  

1. Sponge

Estimated age: Possibly 890 million years
Phylum: Porifera
Class: Calcarea, Hexactinellida, Demospongiae

Spongephoto source: wikipedia.org

Sponges are the oldest surviving sea animals existing today. It is yet not sure how long they have existed in the world, but a fossil found in 2019 suggests they are at least 890 million years old.

Before this recovery, the oldest known sponge fossils were some 535 million years old.

There was a debate about whether life could exist 890 million ago as the oxygen levels on the earth were very low during that time. However, some argue that the earliest lives probably didn’t require as much oxygen as the complicated species needed. 

Sponges play a critical role in structuring deep-water habitats and maintaining marine and freshwater ecosystems. Around 8000 sponge species have been described so far; among them, only 20 are on the list of threatened species.

Did you know?

Sponges do not possess any digestive, nervous, or circulatory systInstead; they maintain a constant water flow in their body that helps them absorb nutrition and oxygen and remove wastes.       



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