Starfish are some of the most fascinating creatures in our oceans. Though they are commonly called starfish, these echinoderms are technically sea stars since they are not fish. Sea stars have captured our imaginations for centuries with their alien appearance and remarkable abilities. From regeneration to reproduction, sea stars continue to astound us.
With their star-shaped bodies and radiating arms, sea stars seem like visitors from another planet. Yet these alien-looking creatures are vital components of marine ecosystems around the world.
Found in intertidal zones, coral reefs, and the deep sea, over 2,000 species of sea stars inhabit all the oceans on Earth. Ranging tremendously in size, shape, and coloration, sea stars continue to fascinate us with their otherworldly anatomy and superpowers.
Sea stars use hundreds of tube feet on their undersides to slowly creep along the seafloor in search of prey. Without blood, brains, or hearts, sea stars have developed ingenious ways to survive the challenges of marine life.
From cloning themselves to eating inside-out, sea stars have remarkable adaptations. Read on to uncover 7 mind-blowing facts about these astonishing echinoderms!
1. Sea Stars Can Regrow Lost Limbs
One of the most astounding facts about sea stars is their ability to regenerate lost limbs 1. If a sea star loses an arm through injury or predation, it can regrow a replacement over several months.
This regenerative power relies on clusters of cells called meristems that act as a reservoir of stem cells. After a limb is lost, the meristem cells near the wound site begin multiplying and differentiating into specialized cells to form a new appendage. Within a year, a fully-formed arm emerges from the stump.
Some sea stars can even regrow an entire body from just a severed limb! Species like the lined sea star (Luidia clathrata) demonstrate this extraordinary regenerative capacity. Detached arms develop into cloned sea stars genetically identical to the original.
2. They Eat Their Food Inside-Out
Sea stars have developed a remarkable technique for consuming prey much larger than their tiny mouths can accommodate. They extend their cardiac stomach out through their mouth and engulf prey such as mussels or clams in it.
Enzymes are released to digest the prey externally before the stomach retracts back into the body with the partially digested meal. This ingenious inside-out eating allows sea stars to fit hefty marine organisms like mollusks and crustaceans into their petite frames.
3. Sea Stars Use Seawater to Pump Nutrients
Instead of blood, sea stars have a water vascular system that utilizes seawater to circulate nutrients throughout their bodies. Seawater enters through a sieve-like plate called a madreporite and flows into canals that extend into each arm.
The water fills thousands of tube feet on the sea star’s underside, enabling movement. The ingenious water vascular system provides necessary nutrients and oxygen while conserving space without a complex circulatory system.
4. They Have Eyespots to Detect Light
Though they lack complex eyes, sea stars have ocelli or eyespots that allow them to sense light and dark. Located on the tips of each arm, the eyespots contain photoreceptor cells and pigment cells.
These primitive visual organs enable sea stars to navigate through their marine environments and detect the shadows of approaching predators. While their vision is limited, the photoreceptive eyespots provide useful information about their surroundings.
5. Sea Stars Can Shed Arms to Escape Predators
Some sea star species can intentionally shed arms through autotomy when attacked by predators. By detaching an arm, a sea star can create a distraction to evade predators.
The severed arm continues to wiggle, keeping the predator occupied as the sea star escapes to safety. The arm will later regenerate, allowing the sea star to survive the encounter. This shedding ability demonstrates the sea star’s clever adaptations for dealing with oceanic threats.
6. There are Over 2,000 Sea Star Species
With over 2,000 species spanning the world’s oceans, sea stars vary tremendously in size, shape, and color. The iconic five-armed sea stars are the most familiar, but species with up to 40 arms exist.
Vibrant reds, oranges, purples, and greens decorate their bodies, while some flaunt bold patterns. Different species inhabit every marine environment, from intertidal pools to the lightless seafloor over 6,000 meters deep. The diversity of sea star species highlights their successful adaptation to the many niches of the oceans.
7. Sea Stars are Keystone Species in Their Ecosystems
Though small, sea stars play an essential role in maintaining balance in their ecosystems. As keystone species, their predatory activities shape the diversity and abundance of other organisms.
For example, sea stars control mussel and clam populations, preventing these invertebrates from taking over rocky intertidal zones. Should sea star populations decline, the ecosystem would undergo dramatic shifts. Their influence far exceeds what their appearance suggests.
Sea stars continue to fascinate us with their evolutionary innovations and ecological importance. From cloning to eating inside-out, they reveal the endless ingenuity of the natural world. These echinoderms remind us that there is still so much to discover in Earth’s oceans.
Next time you spot a sea star in a tide pool or aquarium, take a moment to appreciate the marvels of its existence. Its biology holds enduring mysteries we have only begun to grasp. Let the sea star spark your sense of wonder at life’s incredible diversity.