It depends both on the type of starfish and how
the limbs are lost. As you may know, there are
over 1800 species of starfish and most have the
ability to regrow lost limbs. They can do this
because they keep their vital organs in their arms
(rather their body center), with copies in each
arm. These organs are connected to the digestive
system in the center. If they lose an arm, they
still have all the organs they need to survive
while they regrow it. Losing a limb is a traumatic
experience that leaves the starfish weak and
vulnerable to infection, but some starfish will
voluntarily give up an arm to a predator if it
allows the rest of the starfish to get away.
There is a common misconception that regrown
limbs will always be smaller than the original.
This is not true - limbs will typically be smaller
and weaker as they are growing back, but given
enough time (typically a year or so), you won't be
able to tell which is the newest arm. So, there
is no limit to how many arms a starfish grow back
during its lifetime, as long as it remains healthy
and is given enough time to heal.
But how many limbs can a starfish lose at
once? Regrowing limbs requires time and
energy, so most starfish typically need to keep
least one arm attached to the digestive system in
their main body. This will allow them to eat and
move to find food or hide while they recover.
However, some starfish species don't even need
that much! Instead, a severed arm can grow a whole
new body with additional arms, and become its own
separate starfish! (The limb can't be too damaged
when it is severed, though, or it may not be
healthy enough to regenerate.) Since each arm can
become another identical starfish, so the original
starfish isn't really dead, is it? This
ability to evade death is why it is so difficult
to get rid of invasive starfish species, such as
the Crown of Thorns, that are eating up the
Great Barrier Reef in Australia, with starfish
reproducing faster than the reef can heal.
For more information on the regeneration
process, check out this other ScienceLine
For other facts about starfish, check out starfish , too.
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