<P> Starfish are marine invertebrates . They typically have a central disc and five arms , though some species have a larger number of arms . The aboral or upper surface may be smooth , granular or spiny , and is covered with overlapping plates . Many species are brightly coloured in various shades of red or orange , while others are blue , grey or brown . Starfish have tube feet operated by a hydraulic system and a mouth at the centre of the oral or lower surface . They are opportunistic feeders and are mostly predators on benthic invertebrates . Several species have specialized feeding behaviours including eversion of their stomachs and suspension feeding . They have complex life cycles and can reproduce both sexually and asexually . Most can regenerate damaged parts or lost arms and they can shed arms as a means of defence . The Asteroidea occupy several significant ecological roles . Starfish , such as the ochre sea star ( Pisaster ochraceus ) and the reef sea star ( Stichaster australis ) , have become widely known as examples of the keystone species concept in ecology . The tropical crown - of - thorns starfish ( Acanthaster planci ) is a voracious predator of coral throughout the Indo - Pacific region , and the northern Pacific sea star is considered to be one of the world 's 100 worst invasive species . </P>
<P> Starfish are marine invertebrates . They typically have a central disc and five arms , though some species have a larger number of arms . The aboral or upper surface may be smooth , granular or spiny , and is covered with overlapping plates . Many species are brightly coloured in various shades of red or orange , while others are blue , grey or brown . Starfish have tube feet operated by a hydraulic system and a mouth at the centre of the oral or lower surface . They are opportunistic feeders and are mostly predators on benthic invertebrates . Several species have specialized feeding behaviours including eversion of their stomachs and suspension feeding . They have complex life cycles and can reproduce both sexually and asexually . Most can regenerate damaged parts or lost arms and they can shed arms as a means of defence . The Asteroidea occupy several significant ecological roles . Starfish , such as the ochre sea star ( Pisaster ochraceus ) and the reef sea star ( Stichaster australis ) , have become widely known as examples of the keystone species concept in ecology . The tropical crown - of - thorns starfish ( Acanthaster planci ) is a voracious predator of coral throughout the Indo - Pacific region , and the northern Pacific sea star is considered to be one of the world 's 100 worst invasive species . </P>
how many arms does a sea star have
how many arms does a sea star have
five arms , though some species have a larger number of arms
five arms , though some species have a larger number of arms