Find out all about these incredible
invertebrates!
Grab your snorkels, gang, and join us as we discover the secrets of one of the ocean’s most peculiar
creatures!Ready? Then check out our fascinating starfish facts…Phylum: Echinodermata
Family: Asteriidae Classification: Invertebrate
IUCN status: Not Evaluated
Lifespan (in wild): 35 years
Weight: Up to 5kg
Body size: 1-65cm, depending on species
Diet: Carnivore
Habitat: Ocean
Range:
First things first – despite their common (and very misleading!)name, starfish (or sea stars) are actually
fish. Since theydon’t have a backbone, they belong to a group of species calledinvertebrates, which also
includes urchins and sponges.
There are around 1,600 different species of starfish living in the world’s oceans,where they occupy every type
of habitat including tidal pools, rocky shores,sea grass, kelp beds and coral reefs. Some kinds of starfish
are even found on sandy seabeds 9,000 metres deep! Most starfish sport
spiny skin and five arms surroundinga central disk-shape body – although some can grow as many as 50 arms.
Their arms are covered with pincer-like organs and suckers that allow the animal to slowly creep
along the ocean floor. They also have eyespots on the tips of the arms, which allow the starfish
to sense light and dark,and help it find food.
Favourites on the starfish’s menu include mollusks like clams, oysters and nails.And it has a pretty
impressive way of eating! After attaching its body to the chosen prey,the starfish extends its stomach
out through its mouth. Substances (called enzymes)from the stomach then begin to digest the food.
This allows the nutritious grub to passinsidethe stomach, which in turn retracts back into
the body where digestion is complete. Cool, eh?Tinyorganisms that fall victim to the super starfish
can be swallowed whole.
Starfish predators include certain fish species, sharks, manta rays and even other starfish!To help
protect themselves, these incredible invertebrates have evolved several effectivedefense mechanisms.
As well as theirtough, prickly, armor-like skin, some have striking colours that camouflage
them amongst plantsand coral, or scare off potential attackers.And check this out, too – these cool
creatures are able to regrow lost or damaged limbs!If under attack, some starfish will even shed an arm
to escape the predator. Cunningstuff!
Sand dollars
avoid predators by cloning themselves
Living sand dollars have small spines covering its entire body.They are softer and much shorter than
those of the sea urchin.Like all echinoderms, sand dollars have tube feet.
They are not usedto move around, but simply to breathe.The sand dollar's tube feet actually stick
out of the top ofthe sanddollar. On a sand dollar test, there is usually a patternthat
looks like the petals of a flower. That patternis made up ofmany tiny holes, and it is through these
holes that the sand dollar's tube feet came out when itwas alive.
A sand dollar uses its tiny spines to move around, and to dig into the sand.
It often does this to bury itself in the sand. Sometimes, a sand dollar will
only partially bury itself in the sand, and ends up poking up from the sand,
standing on its side.
On the underside of a sand dollar, there is a star pattern spreading out from
the center where the mouth is. This star pattern is made up of grooves that
are called food grooves. Sand dollars filter sand and water, catching plankton
and other things on their spines. Then, withcilia, the spines move the food
into a food groove, and the food travels down the food groove to the mouth.
Its food consists of crustacean larvae, small copepods, diatoms, algae and detritus.
Phylum: Echinodermata
Family: Asteriidae Classification: Invertebrate
IUCN status: Not Evaluated
Lifespan (in wild): 35 years
Weight: Up to 5kg
Body size: 1-65cm, depending on species
Diet: Carnivore
Habitat: Ocean
Range:
A sand dollar uses its tiny spines to move around, and to dig into the sand.
It often does this to bury itself in the sand. Sometimes, a sand dollar will
only partially bury itself in the sand, and ends up poking up from the sand,
standing on its side.
On the underside of a sand dollar, there is a star pattern spreading out from
the center where the mouth is. This star pattern is made up of grooves that
are called food grooves. Sand dollars filter sand and water, catching plankton
and other things on their spines. Then, withcilia, the spines move the food
into a food groove, and the food travels down the food groove to the mouth.
Its food consists of crustacean larvae, small copepods, diatoms, algae and detritus.