ambulacrum

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. One of the five radial areas on the undersurface of the starfish and similar echinoderms, from which the tube feet are protruded and withdrawn.

Century Dictionary and Cyclopedia

1. n. In zoology, a row, series, or other set of perforations in the shell of an echinoderm, as a sea-urchin or starfish, through which are protruded and withdrawn the tube-feet or pedicels. Each such row or set of holes usually forms a narrow grooved line from base to apex of a sea-urchin, and from the center to the end of each ray of a starfish, along the oral aspect of the body. Each set or radiating series of perforations is an ambulacrum, the several rows together being the ambulacra. The usual definition of ambulacra as the perforated spaces through which the tube-feet are protruded leaves a doubt whether an ambulacrum is not one such perforated space. Ambulacra is sometimes used for the tube-feet themselves, collectively; in which case it properly signifies several sets or series of tube-feet, not several tube-feet of any single row or series.

Wiktionary

1. n. A row of pores for the protrusion of appendages such as tube feet.

GNU Webster's 1913

1. n. 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.
2. n. One of the suckers on the feet of mites.

WordNet 3.0

1. n. one of the five areas on the undersurface of an echinoderm on which the tube feet are located