A genus of sea urchins, similar to Spatangus, abounding in the chalk formation; -- from the starlike disposal of the ambulacral furrows.
These very extensible ambulacral feet, often provided with a suctorial plate at the closed outer end, serve for creeping, sucking, touching, and grasping.
Ambulacral pairs fused to form vertebrae with definite articular surfaces; mouth, radial and genital shields developed, though not all need be present in any one form.
Certain supra-ambulacral plates, which also exist, are not shown.
Radial symmetry affects the food-grooves and, in the more advanced families, the thecal plates; probably also the nerves and ambulacral vessels, but not the gonads.
Pentamerous symmetry affects the food-grooves and thecal plates; probably also the nerves and ambulacral vessels, but not the gonads.
In more typical echinoids the covering-plates alone remained to form the ordinary ambulacral plates, while the flooring-plates disappeared, the canals and other organs remaining as before.
The resemblance of the flooring-plates to the ambulacral ossicles of a starfish is so exact that one can explain it only by supposing similar relations of the water-canals and their branches (podia).
The former might be placed with Diploporita, were it not for a greater intimacy of correlation between ambulacral and thecal structures than is found in Cystidea as here defined.
Among the Holothurias, one particular genus, the Synapta, is distinguished from others of the family by the absence of the ambulacral feet, and by the fact of its uniting both sexes in one individual.
These organs, known as the internal branchiæ, are in communication with the central canal and ambulacral tubes.
The branches of these arms have ambulacral grooves, comprehending a double row of fleshy tentacles, in the centre of which is the ambulacral groove, properly so called, clothed with vibratile cilia over their whole surface.
Certain branching tentacula, which surround the mouth, fashioned like nippers, and the ambulacral tentacles, are its principal organs.
The mouth, in Aristotle's lantern, is in the center of the somewhat concave ventral surface, the petal-like ambulacral zones meeting at the central space.
The body is flat and smooth; the rays sharply pointed and conspicuously bordered with marginal ossicles and fringed with short spines; two rows of ambulacral feet; color rich purple.
If the pyloric caeca be laid back, one can see the rib-like arrangement of the ambulacral ossicles, and also the ampullae, which lie between the ossicles on each side of the ridge.
Ambulacral zones^: The five areas containing the rows of tube-feet.
Ambulacral grooves follow the center of all the arms and branches.
The ambulacral zones are in circles, or petaloid in outline, as in cake-urchins, but are not continuous, and the anterior one is usually unlike the others and frequently without pores.
The ambulacral zones terminate at these ocular plates.
Five of these, alternating with the original diverticula, form the five ambulacral canals, from which diverticula are produced into the ambulacral feet; a sixth gives rise to the Polian vesicle.
The ciliated bands disappear, and a calcareous ring of ten pieces, five ambulacral and five interambulacral, is formed round the oesophagus.
The ambulacral zones which, in the Star-fish, have the shape of a furrow, run along the lower side of each ray (Fig.
All Echinoderms without exception have ambulacral tubes, even though in some there are no external ambulacral suckers connected with them.
It makes no difference whether these lines or patches be painted in the course of the ambulacral feet, or anywhere in the inter-ambulacral spaces.
Now, the point to observe is, that in correlation with this graduated difference in the mobility of the rays, there is a correspondingly graduated difference in the development of the ambulacral system of suckers.
It has therefore been surmised that the function of this tubercle is that of acting as a filter to the sea-water which in large part constitutes the fluid that fills the ambulacral system.
The same observations apply to smaller segments, and even to single detached rows of ambulacral feet.
In Astropecten the ambulacral feet have become partly rudimentary, inasmuch as they have lost their terminal suckers (Fig.
The only other motion exhibited by Echini thus situated is that of a slow rolling movement, now to one side and now to another, according to the prepotency of the pull exerted by this or that row of ambulacral feet.
Taking the common Star-fish as our starting-point, I have already explained the mechanism of its ambulacral system.
This fact proves that the ambulacral feet and the muscles are all held in nervous connection with one another by the external plexus, without reference to the integrity of the main nerve-trunks.
On the oral surface note the centrally-located mouth, the ambulacral grooves, one running longitudinally along each ray, and in each groove two double rows of soft tubular bodies with sucker-like tips.
The water from the outside enters the ambulacral system through a special opening, the madreporic opening, and flowing to the tube-feet helps extend them.
In the starfish we noted five ambulacral areas, one on the under side of each arm; similarly we find five in the sea-urchin.
Each of the five divisions set with pores is called an ambulacral area, while the intervening segments which support the long spines are called the interambulacral areas.
Note the small ocular plate at the tip of each ambulacral area.
In both cases also we find the ocular spots at the tips of the ambulacral areas.
The right-land figure exhibits a single plate from one of the "inter-ambulacral areas.
The left-hand figure shows one of the "ambulacral areas" enlarged, exhibiting the perforated plates.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "ambulacral" in a variety of sentences. We hope that you will now be able to make sentences using this word.
