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Starfish (Sea Star) Profile - from nationalgeographic.com
Marine scientists have undertaken the difficult task of replacing the beloved starfish’s common name
with sea star because, well, the starfish is not a fish. It’s an echinoderm, closely related to sea urchins
and sand dollars.
There are some 2,000 species of sea star living in all the world’s oceans, from tropical habitats to the
cold seafloor. The five-arm varieties are the most common, hence their name, but species with 10, 20, and
even 40 arms exist.
They have bony, calcified skin, which protects them from most predators, and many wear striking colors
that camouflage them or scare off potential attackers. Purely marine animals, there are no freshwater sea
stars, and only a few live in brackish water.
Beyond their distinctive shape, sea stars are famous for their ability to regenerate limbs, and in some
cases, entire bodies. They accomplish this by housing most or all of their vital organs in their arms.
Some require the central body to be intact to regenerate, but a few species can grow an entirely new
sea star just from a portion of a severed limb.
Most sea stars also have the remarkable ability to consume prey outside their bodies. Using tiny,
suction-cupped tube feet, they pry open clams or oysters, and their sack-like cardiac stomach emerges
from their mouth and oozes inside the shell. The stomach then envelops the prey to digest it, and finally
withdraws back into the body and finally withdraws back into the body.
Fast Facts: Type: Invertebrate; Diet: Carnivore; Average lifespan in the wild: Up to 35 years;
Size: 4.7 to 9.4 in (12 to 24 cm); Weight: Up to 11 lbs (5 kg)
Did you know? Sea stars have no brains and no blood. Their nervous system is spread through their arms
and their “blood” is actually filtered sea water.
