from
The Collaborative International Dictionary of English v.0.48
Ambulacrum \Am`bu*la"crum\, n.; pl. {Ambulacra}. [L., an alley
or covered way.] (Zool.)
(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.
[1913 Webster]