starfish have five arms which are hollow and covered with short
spines. Starfish have the ability to take calcium carbonate from
sea water, from this it forms a skeleton connected to calcareous
plates implanted into the skin. Starfish skeletons are commonly
sold as souvenirs in seaside shops.
starfish species predate commercial species of molluscs such as oysters.
If starfish numbers are high enough they can annihilate oyster beds.
In the past when caught by fishermen they would be chopped up and throw overboard in an attempt to reduce numbers. This did not have the
desired affect as starfish have the phenomenal ability to regenerate.
Losing an arm it will regenerate it, but if a single chopped arm
contained a part of the main body it would form a new starfish,
hence numbers just increased. Fortunately for the starfish each arm contains extensions of the
with the sea urchin, star fish movement is driven by a water vascular
system. This system enables the tube feet on the underside of the
arms to contract and elongate. The tube feet have suckers at their
end, on contraction the suckers grip while on contraction they release
their grip. By coordinating the gripping and releasing of the numerous
tube feet, movement is possible.
do not possess jaws and depending on the species digest food in
different ways. Some species turn outward their stomach through
their mouth and completely envelop their prey (shellfish) swallowing
it whole, digesting it, and later regurgitating the shell.
common starfish has perfected the skill of opening bivalves. It
coordinates its tube feet to constantly apply a pull on each valve.
Eventually the bivalve tires and the valves part enough for the
starfish to insert its stomach into the shell. The bivalve’s body
is partially digested and later pulled into the starfish for complete