I think the hydra lacks the specialized cells for touch and chemical detection. On the other hand earthworms have touch, light, vibration and chemical receptors along the entire body surface. Both of them are invertebrates (those animals without a backbone), they include insects, worms, jelly fish, spiders among other animals.
<span><span>The carboxyl end of the G- protein-coupled receptor (GPCR) is located in the cytosol (it is intracellular). Carboxyl terminus is one of the most variable structures of the protein. All of the GPCR are </span><span>structural and functional similar, unlike their ligands.</span></span>
