The Crinoid Water Vascular System
Echinoderms are characterized by a unique
coelomic water vascular system. This is a hydraulically
controlled system consisting of a circumoral ring around the esophogus
with connecting radial canals each leading to an ambulacrum.
The radial canals in crinoids run along each arm into an ambulcral
groove and tube feet. The ambulacral groove with its many cilia
and hydraulically driven tube feet manipulate captured food down
the ambulacral grooves along the arms down to the mouth, situated
at the tegmen which is positioned at the base of the arms.
Echinoderm water vascular systems are either open or closed, crinoids all
have an open water vascular system. If the radial canals run down
the ambulacral grooves and are not covered by plates then the system is
considered "open", if the radial canals are primarily internal and externalized
through pores, the system is "closed".