water enters the vascular system of a starfish through ambulacral grooves.
water enters the vascular system of a starfish through ambulacral grooves.
where does water enter the vascular system of a starfish?
ambulacral grooves
although the contents of the water vascular system are essentially sea water, apart from coelomocytes, the fluid also contains some protein and high levels of potassium salts.









































section::::ophiuroids.









































ophiuroids, the group including brittle stars and basket stars, have a somewhat different water vascular system from sea stars, despite their superficially similar appearance. the madreporite is located on the underside of the animal, usually in one of the jaw plates. the stone canal runs upwards to the ring canal, typically located in a circular depression on the upper (i.e. internal) surface of the jaws. the ring canal has four polian vesicles.
water vascular system
scanning electron microscopy of preserved soft tissues in the single appendage of two genera of stylophorans showed the appendage contained an ambulacral canal with tube feet covered by mobile plates, and was not a tail or stalk with fixed plates covering a notochord or neural tube. the appendage is therefore interpreted as a starfish-like feeding arm. the enlarged base of the arm contains an extension of the body cavity rather than muscle blocks to move a tail; the structure at the base of the arm is most parsimoniously reconstructed as the mouth. stylophorans are therefore reconstructed as true echinoderms of uncertain affiliations, without radial symmetry but with stereom and a water vascular system. the body was oriented with the arm as the anterior end of the animal, which lay on the substrate; food would have been captured by tube feet and moved down the arm to the mouth. some genera may have also used the water vascular system for locomotion. rather than swimming with a muscular post-anal tail as in chordates, mobile genera would have crawled "arm-first" using a water vascular system, like starfish and sea cucumbers.
stylophora