The early nerves include the ring nerve surrounding the future mouth, the radial nerves extending from the ring nerve to the tips of the arms, and the podial nerves extending from the radial nerves to encircle each tube foot
Each tube foot
consists of an enlarged and flattened distal extremity, the disc, which makes contact and attaches to the substratum, the epidermis of the disc encloses a duo-gland adhesive system comprising two types of cells, the ones releasing adhesive secretions and those releasing de-adhesive secretions, allowing sea urchins to attach themselves to substratum (Santos & Flammang 2007).
Basically, each tube foot
contains sucker at the terminal end tips.
Alternatively, because sea urchin tube feet disc photoreceptor cells in vivo connect directly to tube foot
nerves (Ullrich-Luter et al., 2011), the miniature currents we observed may represent synaptic vesicular release from sea urchin tube feet disc cells as part of the expected onward signaling from photoreceptor cells to the rest of the sea urchin nervous system.
The NO synthase inhibitor L-NAME increased sea urchin righting time at 1 mmol [l.sup.-1] but had no detectable effect on righting time at 0.2 mmol [l.sup.-1], indicating a role of NO in tube foot
If tube-foot number (and therefore total area of podial support) varies isometrically with arm length, then the mass supported per tube foot
and per unit podial cross-sectional area will be higher in larger sea stars, which might impair locomotion at larger body sizes.
Evaluation of the different forces brought into play during tube foot
activities in sea stars.
At the base of the tube foot
where the podial NS joined with the radial nerve cords.
Histological sections showed that these tissue layers occupied about 24% and 59%, respectively, of the wall of the ventral tube foot
7b, d), although the fiber plexus in the outer connective tissue of the tentacle appeared to have fewer cells than in the tube foot
The skeletogenesis of the posterodorsal rod, dorsal arch, disk of tube foot
, and spines were observed with differential interference contrast (DIC) microscopy and polarizing microscopy (OPTIPHOT-POL, Nikon, Tokyo, Japan).
In the sea star contact experiments, a single tube foot
was excised from a live sea star, held in self-closing forceps, and brought into contact with the back of the oral hood of a specimen of Melibe.