एक echinoderm के अंडरसुरफेस पर पांच क्षेत्रों में से एक जिस पर ट्यूब पैर स्थित हैं

ambulacra's Usage Examples:

12, D); the ambulacra thus formed are continuous from the peristome to the apical system of plates; the hydropore is connected with a definite plate of that system, and thus marks a secondary bilateral symmetry.

- Pelmatozoa in which the theca is composed of an indefinite number of irregular plates, some of which are variously differentiated in different genera; with no subvective skeletal appendages, but with central mouth, from which there radiate through the theca five unbranched ambulacra, composed of a double series of alternating plates (covering-plates), sometimes supported by an outer series of larger alternating plates (sideplates or flooring-plates).

The stereom of the radials and deltoids on each side of the ambulacra is thrown into folds, running across the radio-deltoid FIG.

The thecal plates, however irregular in some species, always show defined basals and a distinct plate ("radial") at the end of each ambulacrum; they are in all cases so far affected by pentamerous symmetry that their sutures never cross the ambulacra.

- Pelmatozoa in which radial polymeric symmetry of the theca is developed either not at all or not in complete correlation with the radial symmetry of the ambulacra (such as obtains in Blastoidea and Crinoidea); in which extensions of the food-grooves are exothecal or epithecal or both combined, but neither endothecal nor pierced by podia (as in some Edrioasteroidea).

All living, and most extinct, Echinoderms show the following features, almost certainly due to an ancestral pelmatozoic stage: - An incomplete radial symmetry, of which five is usually the dominant number, is superimposed on the secondary bilateralism, owing to the outgrowth from the mouth region of one unpaired and two paired ciliated grooves; these have a floor of nervous epithelium, and are accompanied by subjacent radial canals from the water-ring, giving off lateral podia and thus forming ambulacra, and by a perihaemal system of canals apparently growing out from coelomic cavities.

- Diagrammatic sections across the ambulacra of A, C, Pelmatozoa, and B, D, Eleutherozoa, placed in the same position for comparison.

If this be correct, the only change from Edrioaster, as regards the ambulacra, was that in Palaeodiscus the covering-plates could no longer open, but closed permanently over the whole groove, while the podia issued through slits between them.

Spencer to have had in its ambulacra an inner as well as an outer series of plates.

The fourth class of Pelmatozoa - the Edrioasteroidea - differs from the others in the structure of its ambulacra.

ambulacra's Meaning':

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