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11 Animals With Hydrostatic Skeletons (Pictures)

Animals have different kinds of skeletons, which help them to adapt to their environment. The endoskeleton, which is made up of bones that are inside the body and help them maintain their shape, is the most common type. The exoskeleton is the type of skeleton that covers the animal’s body externally, and the last is the hydrostatic skeleton.

You can probably think of many animals with endoskeletons and exoskeletons, but only a few with hydrostatic ones. Let’s look at some amazing animals with hydrostatic skeletons and how they survive in their environment.

What is a hydrostatic skeleton?

The hydrostatic skeleton is the body structure of animals that gives them a distinct appearance and allows them to survive in their environment. It is a fluid-filled system that allows movement as well as support.

This fluid supports the body, preventing it from collapsing under its own weight and allowing them to contract their muscles to move. Only a few living creatures have hydrostatic skeletons, including octopuses and jellyfish.

11 Animals with hydrostatic skeletons

Here are 11 animals that have this type of skeleton:

1. Hydra

Freshwater hydra
Freshwater hydra | image by Przemysław Malkowski via Wikimedia Commons | CC BY-SA 3.0

Scientific Name: Hydra vulgaris

Hydra is a genus of small freshwater creatures. They’re among the creatures that have hydrostatic skeletons. The hydra’s skeleton is made up of a network of muscles and connective tissue that allows it to contract and expand at will.

This enables them to move quickly in order to avoid predators or catch prey. These small animals feed on small invertebrates, such as worms and insects, that they trap with their tentacles.

There are also 25 Hydra species known, and they reproduce by budding. New hydras usually develop at the junction of the stalk and gastric regions and pinch off as new individuals.

2. Jellyfish

Moon Jellyfish
Moon Jellyfish

Scientific Name: Aurelia aurita

Jellyfish can be found from the surface to the depths of all seas and oceans. There are less than 4000 jellyfish species, each with its own shape and size that sets it apart from the others.

This species has a unique skeleton that’s filled with water, which helps them maintain their shape and prevents them from sinking to the ocean’s bottom. These animals also lack a brain, but they have a sophisticated network of nerves known as a “nerve net” that controls swimming and other behaviors such as feeding and response.

3. Sea anemones

Sea anemones
Sea anemones | image by Bernard Spragg. NZ via Flickr

Scientific Name: Stichodactyla tapetum

Sea anemones are brightly colored animals found at the ocean’s bottom. There are over 1,000 different species of sea anemones, the majority of which live in tropical coastal waters.

These hydrostatic skeleton creatures resemble flowers, with colorful tentacles that look like petals. These animals are available in a variety of colors and maintain their shapes by contrasting different muscles in their bodies.

The hydrostatic skeleton also helps sea anemones in staying upright. Sea anemones feed by capturing tiny plankton and fish with their stinging tentacles.

4. Octopus

Common octopus
Common octopus

Scientific Name: Octopus vulgaris

Octopuses, which have an enormous head, eight arms, and two eyes on either side of the head, are among the most intelligent animals. These creatures are known to fit through the smallest of openings and can even fit through a one-millimeter-wide hole.

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This animal’s hydrostatic skeleton allows its body parts to remain intact even though it lacks bones. Octopuses can live for up to three years and are semelparous, meaning they only reproduce once in their lives. And once they begin to reproduce, their lives begin to end.

5. Flatworms

Persian carpet flatworm
Persian carpet flatworm | image by Pei Yan via Flickr | CC BY-ND 2.0

Scientific Name: Pseudobiceros bedfordi

Flatworms are a type of worm with very simple bodies that lack circulatory and respiratory organs. Depending on the species, they can live in both marine and freshwater environments.

Their bodies are typically flat, but they can also be round or leaf-like. Flatworms also have hydrostatic skeletons, which means flatworms lack bones and rely on pressure to keep them together.

There are over 20,000 species of flatworms in the world today, and their diets vary depending on the type of food supply available in their habitat. Some species consume plant matter, while others consume small animals such as snails or worms.

6. Snails

Garden snail on a log
Garden snail on a log | image by J P via Flickr | CC BY 2.0

Scientific Name: Cornu aspersum

Snails are mollusks with a shell on the back of their bodies. They can be found in freshwater, saltwater, or on land. Plants and other vegetation are eaten by some snails, while others consume animals such as fish, worms, and insects.

Snails have a hydrostatic skeleton, which means that their bodies are filled with water. This enables the animal to move without relying on bones. They can’t move fast, but they can fit through very small spaces (without shells) because they don’t have bones that get stuck in them.

7. Roundworms

Scientific Name: Ascaris lumbricoides

Roundworms are a type of free-living and parasitic worm that can infect humans and other animals. They can be found on land, saltwater, and freshwater, where they feed on fungi, bacteria, and other organic matter. These worms are also more prevalent in tropical regions.

Having a hydrostatic skeleton allows roundworms to move around by contracting their longitudinal muscles. This also makes it easier for them to stretch and squish to fit into tight spaces.

8. Leech

Leech
Leech sucking blood on skin

Scientific Name: Hirudo medicinalis

Leeches are primarily aquatic creatures that live in freshwater. They can attach themselves to fish and other animals thanks to the suckers on their heads, and they can drink blood from them without causing any harm.

These worms have a unique way of moving forward and swimming. They have a hydrostatic skeleton and sucker at each end of their body to help them move forward. Leeches are also interesting animals because they have two hearts, 32 brains, and ten stomachs.

9. Starfish

Seastar eating
Seastar eating | image by NOAA Ocean Exploration via Flickr | CC BY-SA 2.0

Scientific Name: Asterias rubens

One of the most commonly known creatures with radial symmetry is the sea star or starfish. Sea stars are star-shaped marine animals with five arms. They can be found in oceans all over the world, particularly in rocky areas where they feed on mollusks and invertebrates.

Starfish have tube feet and suckers on their arms to pull themselves across the ocean floor, up onto rocks, or onto other surfaces. They also use their tube feet to catch prey and eat their prey by pushing their stomachs out and digesting them outside their bodies.

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10. Slugs

Leopard slug in grassland
Leopard slug in grassland | image by gailhampshire via Flickr | CC BY 2.0

Scientific Name: Limax maximus

Slugs are a type of mollusk with a hydrostatic skeleton, which means the inside of their bodies is filled with water. This allows them to move around in the mud and sludge without fear of their soft organs being squished by their own weight.

You can find these animals in forests and other damp areas where there is plenty of food. They consume plants, fungi, and dead animals. Slugs are also hermaphrodites, meaning they have both male and female reproductive organs.

11. Earthworms

Common earthworm on dried leaves
Common earthworm on dried leaves | image by Donald Hobern via Flickr | CC BY 2.0

Scientific Name: Lumbricus terrestris

Earthworms are invertebrate animals that live in the soil. They’re members of the phylum Annelida, and they can move through their environment by contracting their muscles thanks to their hydrostatic skeleton.

These wriggly creatures are omnivores, which means these worms eat both plants and animals. Their diet consists primarily of decaying organic matter or microscopic animals found in the soil. Earthworms require moisture to breathe through their skin (they have no lungs), so they prefer moist and damp environments.