From the sun-kissed shores to the mysterious depths of the ocean, starfish have long captivated our imagination with their alluring beauty and enigmatic nature. These incredible creatures are more than just pretty sea stars. Let’s embark on a mesmerizing journey with us into the world of starfish, unearthing a treasure trove of lesser-known interesting facts that will leave you in awe.
Class: Asteroidea
1. Starfish is not a Fish
Unlike the name suggests, the starfish is not a fish. It doesn’t possess the essential traits of fish like gills, fins, or scales. The species belong to the phylum Echinodermata, a group of invertebrates that also includes sea urchins, sea lilies, feather stars, sea cucumbers, and sand dollars. They are closely related to brittle stars. They possess a central disc from which their arms radiate. Their upper surface can be either smooth, spiny, or granular, and it is adorned with overlapping plates.
Another difference between fish and starfish, a.k.a sea stars, is their movements. Fish employ their tails to propel themselves through water, whereas sea stars rely on numerous tube feet situated on their underside to move around.
With this distinctive mode of locomotion, they exhibit extraordinary agility in navigating their environment. By utilizing specialized tube feet filled with seawater, these remarkable creatures can traverse the seafloor or reefs with impressive agility, covering an average distance of 15 cm (6 in) per minute.
Thanks to a sticky substance present in their feet, seastars can stick to surfaces such as rocks, without being carried away by waves.
2. There’re 2.000 species of them
There are different types of starfish, around 2,000 species. Some of them are asterina starfish, fromia starfish, rainbow star or red-banded sea star, common or sugar starfish (Asterias rubens), ravioli starfish, mottled sea star, panamic cushioned sea star, the Northern Pacific seastar or Japanese common starfish, doughboy, bloody henry, or goosefoot starfish. To see more about the most beautiful starfish species, you can read here.
The sea creatures exhibit a diverse array of forms, sizes, and colors. Numerous species showcase striking tones of red or orange, some present gentle hues of pink and purple, the others display shades of brown, gray, yellow, or vibrant blue. Furthermore, these colorful creatures boast intricate patterns such as stripes, speckles, and mesmerizing swirls.
The pink starfish, also known as short-spined sea stars or giant pink sea stars, displays a predominantly pink hue. However, some variations feature grayish shadings. On the other hand, the sunflower sea star exhibits a diverse range of colors, ranging from vibrant yellow to orange to shades of red, brown, and occasionally even purple. The blue starfish (Linckia laevigata) is a special species because it’s one of the rare animals with real blue pigments.
Most people think that starfish have 5 arms, however, some species can have more. Take the bat starfish, a.k.a the sea bat, webbed star, or broad-disk star due to its striking resemblance to bat wings, for example. This particular sea star typically boasts between 5 and 9 legs. The carpet sea star has 8 legs.
On the other hand, the crown of thorns starfish (cots) (Acanthaster planci) can possess an impressive array of up to 21 arms. Similarly, the sun sea star has the capacity to have as many as 40 arms. The Antarctic sea star has the most arms – about 50 arms.
Some sea stars are small, but some can weigh up to 11 pounds. Sunflower starfish, or sunflower sea stars, are the biggest species with 16 to 24 limbs that can reach up to 1 meter in length. On the contrary, the paddle-spined sea star is the smallest one with a size of about 5 millimeters.
3. They’re everywhere in the oceans
Sea stars live in every ocean across the globe, spanning from the balmy tropical waters to the frigid depths of the Northern Pacific Ocean. Among these vast bodies of water, the Indo-Pacific Ocean boasts the greatest abundance of sea star species, showcasing remarkable biodiversity.
These creatures thrive exclusively in saltwater habitats and can be observed in a wide range of environments, spanning from coastal areas to the deepest regions of the ocean. They can be found residing in kelp beds, coral reefs, seagrass meadows, tidepools, rocky shores, mud flats, and even deep oceans. Remarkably, certain types of sea stars have been documented inhabiting the deep sea, about 20,000 feet (6,000 meters) below the surface. This is equivalent to approximately 20 times the height of the Eiffel Tower.
One of the amazing adaptions that allows starfish to live in various habitats is their ability to remain outside of the water for extended periods. When they are on the shore due to strong waves and currents or clinging to rocks and pilings during low tide, they can tolerate brief periods out of the water before dying. Larger species can even survive for approximately 28 hours without submersion.
4. They have a Carnivorous diet
Despite their seemingly harmless appearance, starfish feed on animals. These fascinating creatures consume a range of food, including bivalves such as mussels, oysters, barnacles, and clams. They also eat sea pens, small snails, plankton, sea sponges, fish, sea urchins, sea anemones, corals, and astonishingly, even their fellow starfish. Their juveniles have been observed engaging in cannibalistic behavior.
While generally not known for their social tendencies, certain species exhibit a unique behavior of gathering in large groups during specific times of the year for feeding purposes.
One of the most interesting things about these sea stars is their feeding habitat. To catch the prey, they use their arms with tiny suction cups to grip them. Then, they delicately pull the shell of the prey open. Now, the true spectacle unfolds when the sea stars begin to eat and digest their food.
The mouth of these sea creatures is on their underside. However, sea stars do not put food through their mouth like other species. After opening the shell of the prey, starfish protrude their stomach from their mouth, reaching into the shell of the bivalve and completely enveloping the prey. Once the prey is partially broken down, the sea stars retract their stomach back into the digestive system, finalizing the consumption process.
This external feeding behavior enables them to consume larger organisms that would otherwise be too big to fit into their comparatively small mouths.
5. They can detach arms and regenerate them
Starfish have quite a few predators, such as sharks, certain fish species, manta rays, Alaskan king crabs, and even other starfish. To protect themselves, these creatures have developed some unique defense mechanisms.
One strategy is to utilize their existing resources. Sea stars possess a variety of upper surface textures, including smooth, spiny, or granular, which are protected by a robust layer made of calcium carbonate plates and small spines. This calcified and bony skin acts as a strong barrier, effectively defending against potential predators like fish, birds, and sea otters. Some species use their striking and vivid colors, serving either as camouflage or as a deterrent to discourage enemies.
In addition to their physical defenses, sea stars also use some strategies.
– Run away: While they may not match the speed of predators like sharks, starfish can move swiftly enough to escape predators that move slower than them, like other sea stars. With other larger predators, they can seek shelter near rocks or reefs. These crevices are too small for them to get through.
– The survival instincts of starfish extend to their ability to detach arms when under attack. As echinoderms, they exhibit astonishing regenerative capabilities. In the face of a predator’s grasp, the starfish willingly sacrifices the captured arms to secure its own survival. And after that, they can grow new limbs.
Starfish possess remarkable regenerative abilities. Not only can they regenerate fully when severed in half, but they can also regenerate from just a single arm and at least 1 of their central discs. However, this recovery process is quite slow and can span up to a year to complete. What’s even more impressive is that these species are capable of regenerating their neurons, a rare feat seen in only a handful of animal species.
– Burrow under the sand: Certain starfish possess remarkable skills in burrowing into the sand, enabling them to effectively elude the vigilant gaze of predators. Take, for instance, the sand-sifting starfish, when sensing the presence of nearby predators, they skillfully burrow into the sand and cover their bodies with it to hide themselves.
Humans are also their predators. People get them for food, though only parts of their legs are edible. These sea stars are popular street food in Asian countries like Indonesia, Thailand, and China.
6. They Have eyes, but no Blood
Sea stars possess eyes, albeit their eyes differ from ours. The tips of each arm of a sea star feature an eye spot. This means that the number of their eyes will be different, depending on the arm number of each species. For example, a nine-armed sea star has 9 eyes, while a starfish with 40 arms flaunts a total of 40 eyes.
Their eyes look like red spots, acting as simple visual sensors. They can detect light and dark, although their resolution is limited. Although they cannot see like us, these eyes help them perceive their surroundings and move around in the ocean.
Sea stars have a distinctive circulatory system that sets them apart from most animals. Instead of blood flowing through their veins, they depend on a water vascular system. This system consists of interconnected canals that connect to tube feet, enabling the circulation of seawater throughout its body. Since the species take oxygen from water, touching them or bringing them out of water can cause them to suffocate and die. Moreover, the sunscreen and oils from your skin can harm them.
On the starfish’s upper surface, there is a light-colored spot, which is a madreporite or a sieve plate. This madreporite – a specialized entrance – allows the seawater to enter the starfish’s body. As seawater enters the tube feet, it triggers the extension of their arms. Astonishingly, the starfish possesses the ability to manipulate the movements of its tube feet through internal muscles, allowing it to retract the limbs as required.
The filtration system allows seawater to transport nutrients throughout the body and deliver essential substances to different tissues, thereby ensuring the maintenance of their physiological functions.
Despite the absence of a typical brain, heart, and blood, sea stars possess a sophisticated nervous system that enables them to detect and react to external stimuli. Consequently, starfish are capable of experiencing pain and sustaining injuries, contrary to popular belief.
These species are not dangerous, they can’t sting or bite you. However, the thorny starfish possesses venomous spines capable of inflicting a sharp and stinging pain when they penetrate the skin.
7. Reproduction
Sea stars have the remarkable ability to engage in both sexual and asexual reproduction. To sexually reproduce, they release gametes, which are sperm and eggs, into the surrounding water. Fertilization occurs when the sperm meets the eggs, leading to the formation of free-swimming larvae. Over time, these larvae settle on the ocean floor and undergo a developmental process that transforms them into fully-grown adults.
The asexual reproduction of starfish is by fragmentation. If a sea star loses an arm, it can regrow the missing limb, eventually leading to the formation of a fully formed organism. The detached part can develop into a complete individual. This unique capacity for self-regeneration allows starfish to ensure the continuation of their species, even in situations where a mating partner is unavailable.
On average, starfish have a lifespan of approximately 35 years, with the bigger ones living longer than the smaller ones.
8. Threats
Among many starfish species, the sunflower sea star is listed as a critically endangered species on the Red List. This one and the other starfish are facing many threats from their habitat, such as pollution, sea star wasting (SSW) disease or sea star wasting syndrome (SSWS), and the increase in sea temperatures due to climate change. All of these factors affect noticeably in starfish population.
Sea stars play an important role in preserving the well-being of the entire ecosystem, whether it’s through the provision of vital resources to other species or the regulation of other species’ populations. And the decline has a huge impact on these species.
For example, specific types of starfish are essential in maintaining the balance of the population of sea urchins in their local ecosystems. When these keystone species decline in numbers, the sea urchin population proliferates rapidly, leading to excessive grazing of kelp forests. This poses a significant issue as kelp forests play a crucial role as marine habitats, actively sequestering carbon and effectively diminishing pollution levels.
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