American Oceans

Are Starfish Fish

Even though they live under the sea, starfish are not actually considered fish. Starfish are echinoderms, which are marine invertebrates lacking fins, tails, and backbones. As a result, scientists prefer to refer to these creatures as sea stars. 

Are Starfish Fish?

Sea stars can only be found in saltwater. Seawater, rather than blood, is used to pump nutrients through their bodies using a ‘water vascular system.’

Sea stars are relatives of sand dollars, sea urchins, and sea cucumbers, all of which are echinoderms with five-point radial symmetry.

However, this does not imply that all sea stars have five arms; species with ten, twenty, or even forty arms do exist! If one of these limbs is lost, a sea star can miraculously regrow it.

starfish close up with five arms

Sea stars do not have a brain or blood and instead filter saltwater through their bodies. Starfish have been featured in literature, legend, design, and popular culture due to their beautiful symmetrical shape.

They are sometimes gathered as decorations, utilized in design or as branding, and are eaten in some cultures despite their potential toxicity.

These animals have been on Earth for around 500 million years, according to the fossil record (since the Cambrian Period).

starfish in aquarium gathered for decorations

The Cambrian Period, which lasted 53 million years, saw an evolutionary boom of new animals, including our own chordate (backbone-having) ancestors.

How long does a starfish live?

With so many different species of sea stars, it’s difficult to generalize the duration of their lifespan. They can live in the wild for an average of 35 years. When well cared for in captivity, most live 5-10 years.

different species of starfish in coral reefs

Sea stars, like many other marine organisms, are threatened by rising ocean temperatures, acidity and pollution, and other human activities.

Since 2013, a sickness known as sea star wasting illness has resulted in catastrophic population reductions.

It has harmed a variety of animals from New England to Mexico to Alaska. Rising water temperatures, such as those induced by global climate change, aggravate this condition.

sunflower star under the ocean

The extinction of any species has a cascading effect on its habitat. The endangered sunflower star, for example, assisted in the management of sea urchin numbers in kelp forests on the Pacific coast.

Sea urchin populations are expanding and overgrazing the kelp in the absence of their natural predator. This, in turn, kills all animals and living beings that rely on kelp forests.

Sea stars are sensitive to unexpected changes in salinity, oxygen, and pH levels, making them challenging to keep at home.

sea urchin on rock underwater

Some popular species, such as puffers and triggerfish, will consume sea stars and are therefore unsuitable to keep as pets.

Before getting a new pet, always research the animal’s specific needs and whether it is captive-bred or wild-caught.

What is the largest starfish in the world?

The sunflower star (Pycnopodia helianthoides) is the largest known starfish, breaking multiple records.

What is the largest starfish in the world

It has the longest arm spread of any sea star, measuring about 40 inches from tip to tip, and it is also the heaviest, weighing up to 11 pounds. It also has the most arms of any animal known to science.

Aside from its size, the number of arms is what makes this sea star so incredible. Adults have up to 24 symmetrically placed arms, which is more than any other known species.

Because some individuals are a deep yellow, they resemble sunflowers, with all of the arms resembling petals. The hue yellow isn’t the only one available; sunflower stars also come in purple, orange, red, and brown variations.

sunflower star pycnopodia helianthoides underwater

They are paler beneath, with thousands of yellow or orange tubular feet. These feet act like suction cups, providing the sea stars with a firm hold and assisting them in catching and opening their mollusk, sea urchin, and crab prey.

The feet are also utilized for walking, and according to the Monterey Bay Aquarium, this species can travel at a remarkable rate of up to 40 inches per minute.

Why do starfish have 5 arms?

Starfish are marine invertebrates, together with sea cucumbers, sea urchins, and sand dollars. Because of their star-like shape, they are sometimes known as starfish or sea stars. Most sea stars have five arms, but some have ten, twenty, or even forty.

starfish on seaside with ten arms

All starfish look like stars, and while the most common have only five limbs, some of these critters can grow to have up to 40.

The remarkable marine creatures, which are members of the echinoderm family, navigate using their tube feet.

They have unique stomachs that allow them to recover damaged limbs and consume huge prey.

Do starfish crawl or swim?

Starfish do not swim, yet they use an odd method of movement to move around the seafloor or on reefs.

Do starfish crawl or swim?

Starfish move by gliding around the seafloor or the reef’s surface using a complicated water jetting system that shoots water through tunnels in the arms and out via tiny tubes on the bottoms of the arms, which move in waves to propel the animal.

A madreporite is an entrance on the outer edge of a starfish’s core body. This hole draws water into microscopic ducts known as canals. There are three main kinds.

The ring canal transports water from the madreporite to each of the arms, where it is taken down by the radial canals to the lateral canals, which force water into an ampulla, where it is stored.

starfish gliding around the seafloor sand

Water is forced out of the ampulla and through tube feet, causing a segment of tube feet on the bottom of an arm to bend.

The tube foot relaxes after the water stops pumping. The pump-and-relax mechanism causes the tube feet to move in rows in waves, allowing the starfish to glide across the seafloor.

The procedure becomes more fascinating as the sea star changes direction by pushing water through specific tube feet rather than others, causing the animal to move left, right, or backward.

starfish crawl on aquarium glass

The starfish does not swim through the water but rather moves along the surface of the water.

How many eyes do starfish have?

Starfish (or, at least, most starfish) do have eyes — but not where or how many you might think. They have eye “spots” on the tips of each of their limbs.

starfish using its eyes through eye spots

Even though they are primitive, they allow starfish to see and perceive light. There are rare exceptions, however, as certain starfish species lack these eye markings.

These starfish eyes are far from the kinds of eyes we’re used to seeing with our own eyes, but they help answer an age-old puzzle of how these creatures move around and interact with their surroundings.

Starfish are unable to see in color because they lack the requisite cones. Furthermore, their eyes aren’t intended to detect quick motion, so fast-moving objects – their eye spots just work too slowly.

small dot located at starfish limb end

They can see, if the field is clear, 360 Degrees around themselves, but mostly, they can only see light and dark, but not much by way of details and no fast motions at all. They’d never see a fish or seal swim by.

If you look closely at the end of a starfish’s limb, you might notice a small black or red dot the size of a pin-dot.

That’s all there is to it — that’s the eyespot. Each small eye is barely about half a millimeter wide.

starfish crawl at the sea using eyespots

The starfish’s ability to react to light and hazy shape clues collected by its eyespots demonstrates that it has a neural system capable of collecting and evaluating visual information.

What does a starfish eat?

The food that starfish consume varies greatly depending on the species. Some are scavengers, some are predators, and some eat like fish.

crown-of-thorns starfish consumes on coral reefs

Most starfish are predatory and feed on seafloor mollusks like clams, mussels, and oysters. In the wild, a single sea star can consume more than 50 tiny clams in a week.

With no apparent or visible mouth, you may be wondering how starfish eat. Their food is digested in two stomachs: the cardiac stomach and the pyloric stomach.

They will first concentrate their prey with their arms and tubed feet before eating their food. They extend their cardiac stomach out of the prey’s mouth when it gets close enough.

crown-of-thorns starfish finding prey to eat

The stomach seems to be a cloud when stretched. They then partially digest their prey by covering it with their gut.

Once they have digested their food, the cardiac stomach is drawn back into the body, where digestion continues in the pyloric stomach.

This enables them to devour objects considerably larger than themselves by digesting them outside of their smaller mouth and bringing them in once they’ve converted to liquid.

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