\Am`bu*la"crum\, n.; pl. {Ambulacra}. [L., an alley
or covered way.] (Zo["o]l.)
(a) One of the radical zones of echinoderms, along which run
    the principal nerves, blood vessels, and water tubes.
    These zones usually bear rows of locomotive suckers or
    tentacles, which protrude from regular pores. In star
    fishes they occupy the grooves along the under side of
    the rays.
(b) One of the suckers on the feet of mites.