Seastar | Exploring the World of Wildlife: facts about the Seastar

Starfish are beautiful sea creatures found in a variety of colors, shapes, and sizes.

Fact number one.

Sea stars are among the oldest inhabitants of Earth. The first sea stars on Earth appeared 200-250 million years ago. There are about 2,000 known species of starfish, but new ones are discovered from time to time. Not all of them are harmless. All species are predators. Sea stars prey on mussels, mollusks, snails and small fish. Most starfish will even eat their own relatives on occasion.

Fact number two.

Sea stars are not fish. Although sea stars live under water, they are not really fish. They do not have gills, scales, or fins like fish. Sea stars also move differently from fish. While fish move themselves with their tails, starfish have tiny tubular legs that help them move. Because they are not classified as fish, scientists prefer to call them — «starfish. Sea stars are echinoderms. Sea stars belong to the phylum Echinodermata. This means they are related to sea urchins, sea cucumbers and sea lilies. In total, this phylum contains about 7000 species. Many echinoderms exhibit radial symmetry, which means that their body parts are arranged around a central axis. Many sea stars have five-point radial symmetry, because their bodies are made up of five parts. This means that they have no obvious left and right halves, only an upper and lower side. Echinoderms also usually have spines, which are less pronounced in sea stars than in other organisms, such as sea urchins.

Fact number three.

Sea stars are important consumers of carbon dioxide — each year sea stars collectively destroy about 2% of the Earth’s carbon dioxide, which is an extremely large number within an entire planet. Sea stars clean the seafloor of debris, weak and diseased seafloor creatures, and the remains of dead oceanic organisms.

Fact number four.

Sea stars get their name because of their original shape, most of them have 5 limbs, that is, rays. Not all sea races have five arms. Some species have much more than 5 arms, such as the sunstar, which can have up to 40 arms.

Fact number five.

Sea stars can regenerate arms. Surprisingly, sea stars can regenerate lost arms, which is useful if a sea star is injured by a predator. She can lose an arm, escape, and grow a new arm later. Sea stars have most of their vital organs in their hands. This means that some species can even regenerate a whole new starfish from one arm and part of the starfish’s central disc. However, this will not happen too quickly; it takes about a year for the arm to grow back.

Fact number six.

Sea stars have no blood. Instead of blood, sea stars have a system consisting mostly of seawater. Seawater is pumped into the animal’s vascular system through its sieve. This is a kind of trap called a madreporite, which is often visible as a light-colored spot on top of the star. From the madreporite, seawater moves into the sea star’s tubular legs, causing the arm to stretch out. The muscles inside the tubular legs are used to retract the limb.

Fact number seven.

Starfish move using the hundreds of tubular feet located on their underside. The tubular feet are filled with seawater, which the starfish carries through the madreporite on its upper side. Starfish can move faster than you might expect. If you get the chance, visit the tide pool or aquarium and watch the starfish move. It is one of the most amazing sights in the ocean. The tube legs also help the starfish hold its prey, including clams and mussels. Starfish eat with their stomachs outside. If you’ve ever tried to open a clam or mussel shell, you know how difficult it is. However, starfish have a unique way of eating these creatures. A starfish’s mouth is on its underside. When she catches her food, the starfish wraps her arms around the animal’s shell and pulls it out slightly. Then she does something amazing: The starfish pushes her stomach through her mouth, and it enters the shell of the bivalve mollusk. It then digests the animal and inserts the stomach back into its own body. This unique feeding mechanism allows the starfish to eat more prey than it could fit in its tiny mouth.

Fact number eight.

Sea stars have eyes. There are eyes — just not in the place you’d expect. Starfish have eye spots on the end of each arm. That means a five-armed sea star has five eyes, while a forty-armed sun star has 40 eyes. Each starfish eye is very simple and looks like a red spot. It can’t see much detail, but it can sense light and dark, which is good enough for the environment in which the animals live.

Fact number nine.

Sea stars go through five stages of growth before becoming adults — during the first month, stars swim freely and look like jellyfish, they are small, almost invisible to the eye and tiny ocean plants and animals.

Fact number ten.

Sea stars have two ways of reproducing their offspring. Male and female sea stars are difficult to distinguish because they look alike. While many animal species reproduce in only one way, sea stars are slightly different. Sea stars can reproduce sexually. They do this by releasing sperm and eggs (called gametes) into the water. The sperm fertilize the gametes and produce floating larvae that eventually settle to the ocean floor and become adult starfish. Sea stars can also reproduce in the sexual constellation through regeneration, which is what happens when animals lose an arm.

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