Sea stars, also known as starfish, are beautiful and captivating marine animals found in various shapes, sizes, and colors.

These incredible creatures resemble stars and, while the most common species have five arms, some species can grow up to 40 arms! Part of the group of animals called echinoderms, sea stars travel with the help of tube feet.

They are capable of regenerating lost limbs and even use their unique stomachs to swallow large prey.

Sea Stars Are Not Fish

Understanding the Difference

Although sea stars live underwater and are commonly referred to as "starfish," they are not true fish. They lack the features that characterize fish, such as gills, scales, or fins. Unlike fish, which propel themselves using their tails, sea stars move by utilizing tiny tube feet located on their underside. This distinct method of movement and the absence of fish-like features is why scientists prefer to refer to them as "sea stars."

Sea Stars Belong to the Phylum Echinodermata

Relationship with Other Marine Creatures

Sea stars are members of the phylum Echinodermata, meaning they are closely related to other marine animals like sea urchins, sea cucumbers, and sand dollars. There are approximately 7,000 species of echinoderms, many of which display radial symmetry, with their body parts arranged around a central axis.

Most sea stars exhibit five-point radial symmetry, meaning they have five sections and do not have a distinct left or right side, only a top and bottom. Echinoderms typically have spines, although sea stars' spines are less pronounced than those found on creatures like sea urchins.

There Are Thousands of Sea Star Species

Diverse Habitats and Adaptations

There are around 2,000 species of sea stars. While many species live in tropical environments, they can also be found in colder regions, including the polar zones. Some sea stars inhabit the intertidal zone, while others thrive in the deep ocean waters.

These remarkable creatures have adapted to a wide range of environments, displaying incredible diversity in size, shape, and color.

Not All Sea Stars Have Five Arms

Exploring the Variety of Arms

While many people are familiar with the five-armed sea star, not all sea stars fit this description. Some species, such as the sun star, can have up to 40 arms, making them a striking example of nature's variety. The number of arms varies among species, with some sea stars even displaying impressive arm lengths and arrangements.

Sea Stars Can Regenerate Arms

Healing and Survival Mechanism

One of the most amazing features of sea stars is their ability to regenerate lost arms. If a sea star is injured or attacked by a predator, it can lose an arm and escape. Over time, the lost arm will regenerate, a process that can take around a year.

Some species can even regenerate an entirely new sea star from just one arm and a portion of the central disc. This remarkable regenerative ability is vital for survival, ensuring the sea star can recover from injuries.

Sea Stars Are Protected by Armor

Unique Skin and Defense Mechanisms

Depending on the species, sea stars' skin may feel leathery or slightly prickly. Their upper side is covered with tough plates made of calcium carbonate, with tiny spines on the surface. These spines offer protection from predators such as birds, fish, and sea otters. Some sea stars, like the crown-of-thorns starfish, have particularly sharp and spiny features, which provide extra defense.

Facts: The Sea Star (Starfish)

Video by Deep Marine Scenes

Sea Stars Do Not Have Blood

Circulatory System Using Seawater

Dear Lykkers! Instead of blood, sea stars have a unique circulatory system that relies on seawater. This seawater enters the animal's water vascular system through a small opening called the madreporite, often seen as a light-colored spot on the top of the sea star.

The seawater then flows into the tube feet, causing them to extend, and muscles within the tube feet help retract the limbs.

Sea Stars Move Using Their Tube Feet

Movement and Locomotion

Sea stars are equipped with hundreds of tube feet located on their underside, which they use to move. The tube feet are filled with seawater, which the sea star pumps into them through the madreporite. Despite their slow-moving nature, sea stars can cover surprisingly long distances over time. They also use their tube feet to help secure their prey, including clams and mussels.

Sea Stars Eat With Their Stomachs Inside-Out

Amazing Feeding Mechanism

Sea stars prey on bivalves, such as mussels and clams, as well as small fish, snails, and barnacles. When hunting bivalves, sea stars have a fascinating feeding technique. Their mouth, located on the underside, allows them to wrap their arms around a prey's shell and slightly pry it open. The sea star then pushes its stomach through its mouth and into the shell, digesting the animal before retracting the stomach back inside.

Sea Stars Have Eyes

Sensing Light and Dark

Although it may surprise many, sea stars do have eyes. However, these eyes are quite different from those of other animals. They are simple eye spots located at the tips of each arm. A five-armed sea star thus has five eyes. These eyes are capable of detecting light and dark but cannot see in detail, which is sufficient for the sea star's environment.