were studied among a limited number of species, they are found to be highly diverse.
This study bioassays the possible effects of three of these peptides (HYM 194, HYM 330 and HYM 346) on differentiation of specific cell types, nerve cells and nematocytes
, in Hydra vulgaris and Hydra magnipapillata.
The stained cells were distinct from nematocytes
, which were unstained.
Due to this staining, it was not clear if the neurites contacted nematocytes
. No FMRFamide immunoreactivity was present in the exumbrella of Tripedalia or Carybdea.
Cnidocil apparatus: sensory receptor of Physalia nematocytes
Samples were placed in a 1 mol [l.sup.-1] sodium citrate solution for 15 min to induce the nematocytes
to expel the nematocysts.
Biochemical studies have also indicated the presence of a receptor in membrane fractions of hydra that binds to the NMDA channel blocker, MK-801 (Pierobon et al., 2004a), and immunocytochemical studies provided evidence that NMDA receptors exist on the surface of nerve cells, nematocytes
, myonemes of epitheliomuscular cells, and interstitial stem cells (Scappaticci et al., 2004).
The discharge mechanism of acontial nematocytes
involves the release of nitric oxide.
In agonistic interactions, existing stolons swell due to the recruitment of nematocytes
(cells bearing the nematocysts) and discharge of nematocysts (highly specialized stinging organelles) (Buss et al., 1984).
NANA, which mimics the complex molecules containing N-acetylated sugars commonly found on the sea anemones' normal prey (Thorington and Hessinger, 1988), has been found to increase the sensitivity of sea anemone nematocytes
to mechanical stimulation (Thorington and Hessinger, 1988, 1990, 1998; Watson and Hessinger, 1994).
The composition of nematocytes
in the aboral tentacles or their rudiments was examined in star-shaped embryos, preactinulae before liberation, 2-4-h-old larvae, 24-28-h-old larvae, settling larvae, settled individuals, and juvenile polyps 2 days after settlement.
But, by the 2-d stage, hydra have both nematocytes
mounted on tentacles and tentacles long enough to function in feeding (Martin et al., 1997).