The tube foot epithelium is covered by a thin cuticle continuous with that covering adjacent areas of the ambulacrum (See Engster and Brown, 1972, for details).
Such an array consists of connective tissue fibers that wrap the tube foot in both left-and right-hand helices.
The fibers are arranged longitudinally, parallel to the long axis of the tube foot. No striations were observed in the muscle cells.
clathrata and A articulatus the ampullae are bilobed, one lobe extending laterally from the union with the tube foot and the order extending medially [ILLUSTRATION FOR FIGURES 2, 5 OMITTED].
Short lateral canals extend from each side of the radial canal to connect to each tube foot along the length of the arm [ILLUSTRATION FOR FIGURE 7 OMITTED].
The lateral canal joins the tube foot wall at the top of the tube foot.
During such a retraction, the diameter of the tube foot, measured midway between the base and tip, increases from 0.9 to 1.3 mm.
Localized bending typically occurs at the base, while the remainder of the tube foot remains essentially straight and thus pivots about the base.
An individual tube foot first elongates and bends at the base so that the tip of the foot points in the direction of motion.
Tube foot movements during burrowing involve bending away from the ambulacrum toward the sides of the arm.
As a particle of food approaches a given tube foot, it bends toward the particle and protracts until the tip adheres to the food.
clathrata were removed show that contraction of an ampulla occurs during protraction of its associated tube foot and vice versa.