am·bu·lac·rum 
(ăm′byə-lăkrəm, -lākrəm)
(ăm′byə-lăkrəm, -lākrəm)n. pl. am·bu·lac·ra (-lăkrə, -lākrə)
One of the five radial areas on the undersurface of the starfish and similar echinoderms, from which the tube feet are protruded and withdrawn.
[Latin ambulācrum, walk planted with trees, from ambulāre, to walk; see ambhi in the Appendix of Indo-European roots.]
am′bu·lacral adj.
ambulacrumventral view of a starfish arm