Starfish are among the most fascinating and mysterious creatures of the oceans. Belonging to the class Asteroidea, these marine invertebrates captivate both children and adults with their five-armed star shapes and vibrant colors. There are approximately 1,500 different starfish species worldwide, inhabiting a broad range of environments from tropical coral reefs to the cold polar seas. Starfish are considered a “keystone species” in marine ecosystems because they play a critical role in maintaining the biological balance of their habitats.
What Are the Characteristics of Starfish?
Starfish are invertebrate marine animals from the phylum Echinodermata. They typically have a central disc with five arms extending outward, although some species can have 7, 10, or even up to 40 arms. The upper surface of their bodies can be smooth, grainy, or spiny and features a skeleton made of calcareous plates.
One of the most remarkable features of starfish is their hydraulic movement mechanism known as the “water vascular system.” This system allows them to control hundreds of tube feet located on the underside of their arms, enabling them to move along the seabed, cling to rocks, and capture prey. The suction cup-like structures at the ends of the tube feet provide them with a powerful grip.
Starfish display an array of colors—red, orange, yellow, purple, blue, and brown. These vivid hues serve both as camouflage and as a warning to potential predators.
How Do Starfish Feed?
Starfish are usually carnivorous, and their feeding habits are truly unique. Their primary food sources include mussels, oysters, marine mollusks, small fish, sea urchins, and coral polyps. Some species are omnivorous, feeding on algae and organic debris.
Their distinctive feeding method involves extending their stomachs outside their bodies. When preying on a mussel or oyster, they use their strong arms to pry open the shell, insert their stomach inside, and digest their prey externally. This process can take hours, but starfish are patient hunters.
Where Do Starfish Live?
Starfish can be found in all the world’s oceans, from shallow tidal pools to the dark seafloor at depths of 6,000 meters. The greatest diversity of species is found in tropical coral reefs, but rocky shores, sandy bottoms, kelp forests, and even polar seas are also starfish habitats.
At Emaar Aquarium, you can observe starfish in the Rocky Shores section, where specially designed tanks mimic their natural environment.
How Do Starfish Reproduce?
Starfish have both sexual and asexual reproductive abilities. In sexual reproduction, males and females release sperm and eggs into the water, where fertilization occurs externally. The fertilized eggs develop into larvae that drift as plankton for a while before undergoing metamorphosis to become the familiar star shape.
Asexual reproduction occurs through “regeneration,” one of the most astonishing abilities of starfish. If a starfish loses an arm, it can regrow it. In some species, if a detached arm contains part of the central disc, it can develop into a completely new individual. This extraordinary regenerative capacity has inspired research in regenerative medicine.
Types of Starfish
More than 1,500 starfish species have been identified worldwide. Each species has adapted distinct characteristics based on its habitat:
Red Starfish (Fromia milleporella):
This species, known for its bright red color, inhabits coral reefs of the Indo-Pacific. It is one of the most popular species among aquarium enthusiasts.
Blue Starfish (Linckia laevigata):
Easily recognized by its vibrant blue color, this species lives in shallow waters of the tropical Pacific and Indian Oceans and feeds on algae and organic matter.
Sun Starfish (Solaster spp.):
Usually possessing 10-12 arms, this active predator is found in northern seas and can even feed on other starfish.
Crown-of-Thorns Starfish (Acanthaster planci):
This large species can have up to 21 arms and feeds on coral polyps. When its population explodes, it can cause severe damage to coral reefs.
Leather Starfish (Dermasterias imbricata):
This species, with a soft and slippery outer surface, is found along Pacific coasts and can feed on jellyfish.
Chocolate Chip Starfish (Protoreaster nodosus):
Known for its brown and cream color and bumpy texture, this species inhabits the sandy and grassy sea floors of Southeast Asia.
Are Starfish Poisonous?
Most starfish species are harmless to humans. However, some, especially the Crown-of-Thorns Starfish (Acanthaster planci), have sharp, venomous spines. Contact can cause pain, swelling, and infection. Many starfish also produce chemicals called “saponins,” which taste unpleasant and deter predators.
When encountering starfish in the wild, it is safest to observe rather than touch. At Emaar Aquarium, you can get an up-close look at starfish in a secure environment guided by experts.
Do Starfish Have a Heart or Brain?
Starfish do not have a heart or brain as we know them. Instead of a central nervous system, they possess a network of nerves distributed throughout their bodies, allowing them to respond to environmental stimuli. Instead of blood, seawater circulates through their water vascular system, fulfilling both movement and respiratory functions.
Each arm ends with “eye spots” that are sensitive to light, helping the starfish sense their surroundings. Their tube feet are sensitive to chemicals, enabling them to detect food sources by smell.
How Long Do Starfish Live?
The lifespan of a starfish varies by species. Smaller species typically live 5-10 years, while some larger ones can survive up to 35 years. Factors affecting their longevity include species, habitat conditions, food availability, and predation pressure.
Starfish and the Ecosystem
Starfish play a vital role in maintaining balance within marine ecosystems. By keeping populations of bivalves like mussels and oysters in check, they prevent these species from overpopulating and displacing other marine life. That’s why they are called “keystone species”—they have a disproportionately large impact on their ecosystem.
However, climate change, ocean acidification, and habitat loss threaten starfish populations. In recent years, a disease known as “starfish wasting syndrome” has led to the death of millions of starfish along North America’s coasts.
Frequently Asked Questions
Are starfish fish?
No, starfish are not fish. They are invertebrate marine animals belonging to the phylum Echinodermata and are closely related to sea urchins and sea cucumbers.
Will a starfish die if taken out of water?
Starfish cannot survive out of water for long. They respire through papulae on their skin rather than gills, and these structures dry out quickly. A few minutes out of water is usually harmless, but prolonged exposure can be fatal.
Can you eat starfish?
In some cultures, especially in China, Japan, and Indonesia, starfish are consumed as food. However, many species contain toxins and require specific preparation before being eaten.
How many arms does a starfish have?
Most starfish species have five arms, but the number can range from four to forty. Sun starfish typically have 10-12 arms, while Crown-of-Thorns starfish can have up to 21 arms.
What happens if a starfish loses an arm?
Starfish have remarkable regenerative abilities. A lost arm can regrow within a few months. In some species, if the detached arm contains part of the central disc, a new individual can develop from it.
Can you keep a starfish in a home aquarium?
Yes, certain starfish species can be kept in saltwater aquariums. However, it is important to monitor water quality, salinity, and dietary needs. Aquarium starfish typically eat algae, shellfish, and specialized foods.
Emaar Aquarium and Underwater Zoo is home to many marine species. Visit our Our Species page to discover more.
