In technical language, the surface from which these fleshy threads protrude, are called ambulacral areas, and the spaces between, interambulacral areas.    From Wordnik.com.  [Report of the North-Carolina Geological Survey. Agriculture of the Eastern Counties: Together with Descriptions of the Fossils of the Marl Beds] Reference

Echinoderms the interambulacral plates are absent; there are no rows of plates of a different kind alternating with the ambulacral ones, as in the Sea-Urchins and the Star-Fishes, but the ab-oral region closes immediately upon the ambulacra.    From Wordnik.com.  [The Atlantic Monthly, Volume 10, No. 57, July, 1862] Reference

The ambulacral areas are narrow, but the poriferous zones are rather wide; and the interambulacral areas are about four times as wide as the ambulacral.    From Wordnik.com.  [Report of the North-Carolina Geological Survey. Agriculture of the Eastern Counties: Together with Descriptions of the Fossils of the Marl Beds] Reference

(combs), from which they take their name of Ctenophorae, with the ambulacral (locomotive) apparatus of the echinoderms.    From Wordnik.com.  [Louis Agassiz: His Life and Correspondence] Reference

Four views, a, Echinus Ruffinii, viewed from above; b, mouth; c, spinegerous tubercles; d, ambulacral plates, and arrangement of pores: a, b, natural size, c, d, enlarged.    From Wordnik.com.  [Report of the North-Carolina Geological Survey. Agriculture of the Eastern Counties: Together with Descriptions of the Fossils of the Marl Beds] Reference