Humans have always been fascinated by the many stars God placed in the night sky. In the Bible
we read, “He telleth the number of the stars; he calleth them all by their names.” This same wonder
extends to the abundant stars God placed in the oceans, the sea stars, commonly known as starfish.
Starfish belong to the scientific class called Asteroidea, meaning “like a star” in Latin.
However, instead of filling the night sky, these sea stars fill the oceans of the world
with their interesting shapes, beautiful colors, and fascinating behaviors.
While starfish may look simple, their bodies and behaviors are actually quite complex.
Despite the name, starfish are not fish at all! They are actually echinoderms.
Echinoderms are marine animals with spiny skin
and include other creatures like sand dollars, sea urchins, and sea cucumbers.
An astounding two thousand different species of starfish live in the ocean, in environments
ranging from warm tropical seas to the chilly seafloor. They are found in almost every ocean
habitat, including coral reefs, tide pools, kelp beds, in sea grass, and on rocky shores.
Starfish typically live up to 35 years in the wild and can weigh up to 5 kilograms
(or 11 pounds). That’s about the weight of a large watermelon! While one species is so tiny
it could fit on your fingernail, most species of starfish range from about 5 to 10 inches across,
from the size of a young child’s hand to the size of a large man’s hand.
Starfish can vary widely in appearance as well as size. You may have seen a starfish with five arms,
which is the most common arrangement, but some species have 10, 20, or even 50 arms!
At the end of each of these arms there are tiny suction cups that allow them to hold onto prey.
These arms are surprisingly strong. They can grasp onto a mollusk shell and pry it
open to eat what’s inside. Mollusks are a favorite snack for starfish,
and the most commonly eaten varieties are clams, oysters, and snails.
The way starfish eat is in itself an unusual process. Starfish have two stomachs,
one of which extends out through its mouth and covers the edible part of its prey. Then,
powerful digestive enzymes break down the food. Finally, this stomach is pulled back
into the body of the starfish through its mouth where the food is transferred to the next stomach.
Starfish find their food by sensing light through eyespots on the tips of the arms.
The distinctive body of a starfish starts with a central disk, or circle, with the mouth in the
middle on the underside. From this disk radiate five or more arms. Hundreds of tiny tube feet are
arranged along the center of each arm. The tube feet not only allow the animal to hold onto food,
they also allow it to move, attach to surfaces, and transfer food to its mouth.
Most species of starfish have the unique ability to regenerate, or regrow, parts of their body
including the arms. Starfish can also shed an arm in defense. For example,
if a starfish arm is grabbed by a predator, the starfish can break off its own arm to get away
and grow a new one over several months or years. Imagine if humans could do that!
Inside its body, starfish have no brains and no blood. With no brain, the starfish cannot plan
its movements. Instead, it relies on its complex nervous system, including nerves that run down
each arm to help it respond to sensations such as light or touch. Instead of blood,
starfish pump seawater throughout their bodies in order to transport nutrients.
Outside the body are spines called spicules. These poky extensions keep other hungry animals at bay,
and potential predators may think twice before snacking on the spiny starfish. This is one reason
why the starfish is a critical part of its marine ecosystem. They are known as keystone predators.
Keystone predators are the dominant predators that assist with eating prey that could otherwise
become too numerous, therefore maintaining the delicate balance of the seafloor community.
However, starfish are definitely not social creatures;
they are solitary, living most of their lives alone. They will, however,
gather together to feed at certain times of the year, attracted by the same food sources.
Perhaps because they remind us of the twinkling stars in the night sky,
starfish—the stars of the sea-- captivate us with their unique shape, colors, and characteristics.